viirya commented on code in PR #58978:
URL: https://github.com/apache/spark/pull/58978#discussion_r4321763048


##########
sql/core/src/main/scala/org/apache/spark/sql/execution/python/InProcessPythonUDFBuilder.scala:
##########
@@ -0,0 +1,144 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.python
+
+import java.util.{Collections, List => JList}
+
+import scala.jdk.CollectionConverters._
+import scala.util.Try
+
+import org.apache.spark.{SparkEnv, SparkException}
+import org.apache.spark.api.python.{PythonEvalType, SimplePythonFunction}
+import org.apache.spark.internal.config.PLUGINS
+import org.apache.spark.internal.config.Python.PYSPARK_EXECUTOR_MEMORY
+import org.apache.spark.sql.Column
+import org.apache.spark.sql.catalyst.expressions.PythonUDF
+import org.apache.spark.sql.catalyst.plans.logical.NamedParametersSupport
+import org.apache.spark.sql.catalyst.util.CharVarcharUtils
+import org.apache.spark.sql.classic.{ColumnNodeExpression, ExpressionUtils}
+import org.apache.spark.sql.errors.QueryCompilationErrors
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types.DataType
+import org.apache.spark.util.Utils
+
+/**
+ * JVM-side builder for in-process [[PythonUDF]] expressions, called from the 
Python API
+ * via py4j's JVM reflection bridge 
(``sc._jvm.org.apache.spark...InProcessPythonUDFBuilder``).
+ *
+ * Each Python wrapper calls `create` once, with Java-typed arguments as 
passed by PySpark's
+ * ``sc._jvm`` proxy, and keeps the returned [[InProcessPythonFunction]]. Each 
call of the
+ * wrapper then applies that function to its columns, which returns a 
[[Column]] backed by a
+ * [[PythonUDF]] with the in-process evaluation type, so that all of them 
share one command.
+ */
+object InProcessPythonUDFBuilder {
+
+  /**
+   * Creates an in-process Python UDF, once per Python wrapper, so that its 
command crosses
+   * py4j and lives in the driver once however many expressions call it.
+   *
+   * @param name            display name (Python function ``__name__``)
+   * @param serializedFunc  cloudpickle bytes of the Python UDF
+   * @param returnTypeJson  JSON string of the Spark SQL return type
+   * @param pythonVersion   driver's Python major.minor version
+   */
+  def create(
+      name: String,
+      serializedFunc: Array[Byte],
+      returnTypeJson: String,
+      pythonVersion: String): InProcessPythonFunction = {
+    val returnType = DataType.fromJson(returnTypeJson)
+    // As in `UserDefinedPythonFunction.builder`, so that no client can skip 
its own check.
+    if (CharVarcharUtils.hasCharVarcharIncludingUDT(returnType)) {
+      throw QueryCompilationErrors.charVarcharNotSupportedInPython(
+        "Python UDF return types", returnType.catalogString)
+    }
+    val function = new SimplePythonFunction(
+      serializedFunc,
+      Collections.emptyMap[String, String](),
+      Collections.emptyList[String](),
+      "",
+      pythonVersion,
+      Collections.emptyList(),
+      null)
+    new InProcessPythonFunction(name, function, returnType)
+  }
+
+  private val UnsupportedSessionConfiguration =
+    "INVALID_SPARK_CONFIG.UNSUPPORTED_IN_PROCESS_PYTHON_UDF"
+
+  /**
+   * Whether `checkConfiguration` rejected unsupported settings. When another 
session re-plans
+   * an in-process UDF, only its session settings can newly fail: the 
SparkConf settings and
+   * the plugin are the same as when the UDF was first planned.
+   */
+  private[sql] def isUnsupportedSessionConfiguration(e: SparkException): 
Boolean =
+    e.getCondition == UnsupportedSessionConfiguration
+
+  private[sql] def checkConfiguration(conf: SQLConf): Unit = {
+    val sparkConf = Option(SparkEnv.get).map(_.conf)
+    // The legacy profilers wrap the function with an accumulator, which is 
not supported.
+    val legacyProfilers = Seq("spark.python.profile", 
"spark.python.profile.memory")
+      .filter(key => sparkConf.exists(_.getBoolean(key, false)))

Review Comment:
   Thanks, fixed in 8aead4b as suggested: the check is now 
`sparkConf.exists(_.get(key, "false") == "true")`, the condition PySpark uses. 
"legacy Python profilers are rejected" also checks that `True`, `0` and `off` 
pass `checkConfiguration`; with `getBoolean`, `True` is rejected and `0` throws.



##########
sql/core/src/main/scala/org/apache/spark/sql/execution/python/InProcessPythonRuntime.scala:
##########
@@ -0,0 +1,416 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.python
+
+import java.io.File
+import java.util.concurrent.{Callable, ExecutionException, Executors, 
ThreadFactory, TimeoutException, TimeUnit}
+import java.util.concurrent.atomic.AtomicInteger
+
+import scala.collection.mutable
+import scala.jdk.CollectionConverters._
+
+import jep.{JepConfig, JepException, MainInterpreter, 
NamingConventionClassEnquirer, PyConfig, SharedInterpreter}
+import org.apache.arrow.c.{ArrowSchema, Data}
+import org.apache.arrow.vector.types.pojo.Field
+
+import org.apache.spark.{TaskContext, TaskKilledException}
+import org.apache.spark.api.python.{PythonException, PythonUtils}
+import org.apache.spark.internal.Logging
+import org.apache.spark.internal.config.Python
+import org.apache.spark.sql.util.ArrowUtils
+import org.apache.spark.util.Utils
+
+/** Owns one interpreter generation per executor plugin lifecycle. */
+private[python] object InProcessPythonRuntime extends Logging {
+  private val TRACEBACK_SENTINEL = "__INPROCESS_UDF_TRACEBACK__:"
+  private var active: InterpreterSession = _
+  private var mainConfigured = false
+  @volatile private var sharedConfigured = false
+  @volatile private var bootstrappedSitePackages: Option[Seq[String]] = None
+
+  private[python] class LifecycleException(message: String) extends 
IllegalStateException(message)
+
+  // Keep JEP references out of the singleton's verifier so currentSession can 
report
+  // an uninitialized runtime even when the provided JEP JAR is absent.
+  private[python] object InterpreterConfiguration {
+    def configure(sitePackages: Seq[String]): Unit = {
+      if (!mainConfigured) {
+        // Like Python workers, use a stable default hash seed on every 
executor. This must
+        // happen before JEP creates its process-wide main interpreter, 
including on restarts.
+        MainInterpreter.setInitParams(
+          
PyConfig.isolated().setUseEnvironment(false).setHashSeed(0).setUseHashSeed(true))
+        mainConfigured = true
+      }
+      if (!sharedConfigured) {
+        // JEP imports its Python package during construction, before our 
bootstrap runs.
+        SharedInterpreter.setConfig(interpreterConfig(sitePackages))
+      }
+    }
+
+    def interpreterConfig(sitePackages: Seq[String]): JepConfig = {
+      require(sitePackages.forall(Python.isValidInProcessPath), 
Python.IN_PROCESS_PATH_RULE)
+      val config = new JepConfig().setClassEnquirer(new 
NamingConventionClassEnquirer(false))
+      // Calling addIncludePaths with no arguments adds the working directory 
in JEP.
+      if (sitePackages.nonEmpty) config.addIncludePaths(sitePackages: _*)
+      config
+    }
+  }
+
+  private class ManagedSharedInterpreter extends SharedInterpreter {
+    override protected def configureInterpreter(config: JepConfig): Unit = {
+      // JEP invokes this hook after native initialization, from its 
constructor. Close
+      // here if configuration fails, before the caller can receive an 
interpreter handle.
+      try {
+        super.configureInterpreter(config)
+        sharedConfigured = true
+      } catch {
+        case t: Throwable => Utils.tryWithSafeFinally { throw t } { close() }
+      }
+    }
+  }
+
+  private[python] def bootstrapScript(script: String): String = {
+    "try:\n" + script.linesIterator.map("    " + _).mkString("\n") +
+      "\nexcept BaseException as _bootstrap_error:\n" +
+      "    raise RuntimeError('In-process Python bootstrap failed: ' + " +
+      "ascii(type(_bootstrap_error).__name__ + ': ' + str(_bootstrap_error))) 
from None\n"
+  }
+
+  def initialize(sitePackages: Seq[String] = Seq.empty): Unit = synchronized {
+    bootstrappedSitePackages.foreach { paths =>
+      if (paths != sitePackages) {
+        throw new LifecycleException("In-process Python has already configured 
different " +
+          "sitePackages. Restart the executor process before changing 
interpreter configuration.")
+      }
+    }
+    if (active != null && !active.isTerminated) {
+      // The sitePackages were checked above: an active session bootstrapped 
them.
+      active.requireRunning()
+    } else {
+      InterpreterConfiguration.configure(sitePackages)
+      val candidate = new InterpreterSession(sitePackages)
+      try {
+        candidate.initialize()
+        active = candidate
+      } catch {
+        case t: Throwable => Utils.tryWithSafeFinally { throw t } { 
candidate.shutdown() }
+      }
+    }
+  }
+
+  def currentSession: InterpreterSession = synchronized {
+    checkState(active != null)
+    // `shutdown` keeps the stopped session, so a session that is not running 
was stopped.
+    checkState(active.isRunning, StoppedMessage)
+    active
+  }
+
+  def shutdown(): Unit = {
+    val session = synchronized { active }
+    if (session != null) session.shutdown()
+  }
+
+  private def checkState(running: Boolean): Unit = {
+    checkState(running, "In-process Python is not running; initialize the 
executor plugin first")
+  }
+
+  private val StoppedMessage =
+    "In-process Python has been stopped (executor or SparkContext shutdown)"
+
+  private def checkState(running: Boolean, message: String): Unit = {
+    if (!running) throw new IllegalStateException(message)
+  }
+
+  /**
+   * Tasks retain this generation, so stale tasks cannot enter a later 
SparkContext's interpreter.
+   * Lifecycle operations only hold the monitor while enqueueing work, never 
while running Python.
+   */
+  private[python] class InterpreterSession(val sitePackages: Seq[String] = 
Seq.empty) {
+    // CPython native calls need more stack than the usual JVM thread default. 
This is a
+    // platform-dependent size request, not protection against arbitrary 
native crashes.
+    private val executor = Executors.newSingleThreadExecutor(new ThreadFactory 
{
+      override def newThread(runnable: Runnable): Thread = {
+        val thread = new Thread(null, runnable, "inprocess-python", 8L * 1024 
* 1024)
+        thread.setDaemon(true)
+        thread
+      }
+    })
+    @volatile private var running = true
+    // Calls submitted to the interpreter thread that have not finished or 
been cancelled.
+    private val pendingCalls = new AtomicInteger()
+    // Accessed only on the owning thread.
+    private var interp: SharedInterpreter = _
+    // Guarded by this session's monitor. Shutdown must keep Python-owned 
result buffers
+    // pinned until their tasks have released the JVM CDI references.
+    private val registeredHandles = mutable.Set.empty[String]
+
+    def isRunning: Boolean = running
+    def isTerminated: Boolean = executor.isTerminated
+
+    def requireRunning(): Unit = {
+      if (!isRunning) {
+        throw new LifecycleException("In-process Python is still stopping. 
Wait for outstanding " +
+          "native work to finish or replace the executor process before 
starting a new context.")
+      }
+    }
+
+    private[python] def onInterpreterThread[T](body: => T): T = {
+      val context = Option(TaskContext.get())
+      context.foreach(_.killTaskIfInterrupted())
+      val gate = new Object
+      var started = false
+      var cancelled = false
+      val future = synchronized {
+        checkRunning()
+        pendingCalls.incrementAndGet()
+        executor.submit(new Callable[T] {
+          override def call(): T = {
+            gate.synchronized {
+              if (cancelled) throw new TaskKilledException("Cancelled before 
Python invocation")
+              started = true
+            }
+            try body finally pendingCalls.decrementAndGet()
+          }
+        })
+      }
+      var interrupted = false
+      try {
+        while (true) {
+          val taskCancelled = context.exists(_.isInterrupted())
+          if (interrupted || taskCancelled) {
+            val cancelledBeforeStart = gate.synchronized {
+              if (started) false else {
+                cancelled = true
+                future.cancel(false)
+                pendingCalls.decrementAndGet()
+                true
+              }
+            }
+            if (cancelledBeforeStart) {
+              context.foreach(_.killTaskIfInterrupted())
+              throw new InterruptedException("Cancelled before Python 
invocation")
+            }
+          }
+          try {
+            val result = future.get(100, TimeUnit.MILLISECONDS)
+            context.foreach(_.killTaskIfInterrupted())
+            return result
+          } catch {
+            case _: TimeoutException =>
+            case _: InterruptedException => interrupted = true
+            case e: ExecutionException => throw e.getCause
+          }
+        }
+        throw new IllegalStateException("Unreachable")
+      } finally {
+        // Once native work starts, wait for it even after cancellation: the 
caller still owns
+        // CDI structs that Python may use. Pending work, however, is safe to 
cancel immediately.
+        if (interrupted) Thread.currentThread().interrupt()
+      }
+    }
+
+    def initialize(): Unit = onInterpreterThread {
+      val candidate = new ManagedSharedInterpreter()
+      // SharedInterpreter keeps sys.modules and sys.path for the JVM 
lifetime, even when
+      // the following bootstrap fails. A new context cannot switch Python 
environments.
+      bootstrappedSitePackages = Some(sitePackages)

Review Comment:
   Thanks, the stale path is real: I added a module that only the failed 
configuration's directory has to 
`test_fresh_jvm_retries_configuration_without_spark_home`, and the retried 
interpreter imported it. I kept the retry itself, though, since R4 
(https://github.com/apache/spark/pull/58978#discussion_r4110615664) asked that 
a configuration that fails because JEP is missing, e.g. a typo in 
`sitePackages`, can be fixed without restarting the JVM, and pinning when 
`setConfig` is called would undo that. Instead, in b33b115 the runtime records 
every `sitePackages` it gives to JEP, and the bootstrap of a retry removes from 
`sys.path` the ones that it does not configure again, before it applies the new 
ones. The test now also checks that the module is not importable after the 
retry, and fails without the change. Once a configuration succeeds, 
`bootstrappedSitePackages` still pins it as before.



##########
sql/core/src/main/scala/org/apache/spark/sql/execution/python/InProcessArrowEvalPythonEvaluatorFactory.scala:
##########
@@ -0,0 +1,581 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.python
+
+import java.io.File
+import java.nio.file.Files
+import java.util.UUID
+import java.util.concurrent.TimeUnit
+import java.util.concurrent.atomic.{AtomicBoolean, AtomicInteger}
+import java.util.concurrent.locks.ReentrantLock
+
+import scala.collection.mutable.ArrayBuffer
+import scala.jdk.CollectionConverters._
+
+import com.google.common.util.concurrent.Uninterruptibles
+import org.apache.arrow.c.{ArrowArray, ArrowSchema, BaseStruct}
+import org.apache.arrow.util.AutoCloseables
+import org.apache.arrow.vector.VectorSchemaRoot
+
+import org.apache.spark.{SparkEnv, SparkException, TaskContext}
+import org.apache.spark.api.python.ChainedPythonFunctions
+import org.apache.spark.memory.MemoryConsumer
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.{Attribute, Expression, 
JoinedRow, PythonUDF, UnsafeProjection, UnsafeRow}
+import org.apache.spark.sql.execution.arrow.ArrowWriter
+import org.apache.spark.sql.execution.metric.SQLMetric
+import org.apache.spark.sql.execution.python.EvalPythonExec.ArgumentMetadata
+import org.apache.spark.sql.types._
+import org.apache.spark.sql.util.ArrowUtils
+import org.apache.spark.sql.vectorized.{ArrowColumnVector, ColumnarBatch, 
ColumnVector}
+import org.apache.spark.util.Utils
+
+/**
+ * Evaluates scalar Python UDFs using Arrow CDI in the executor process. Only 
UDF arguments
+ * are converted to Arrow. Original rows are buffered in a spillable queue and 
joined with
+ * the results, unless all of them are UDF arguments that read back from Arrow 
unchanged.
+ * Each batch owns its Arrow buffers so Python can safely retain input arrays.
+ *
+ * The evaluator owns its queue, so that cleanup at task completion is 
coordinated with a
+ * consumer on another thread, such as a pipelined Python writer or a 
TRANSFORM feed thread.
+ */
+class InProcessArrowEvalPythonEvaluatorFactory(
+    childOutput: Seq[Attribute],
+    udfs: Seq[PythonUDF],
+    output: Seq[Attribute],
+    batchSize: Int,
+    maxBytes: Long,
+    timeZoneId: String,
+    largeVarTypes: Boolean,
+    hideTraceback: Boolean,
+    simplifiedTraceback: Boolean,
+    tracebackWithLocals: Boolean,
+    fullValidation: Boolean,
+    metrics: Map[String, SQLMetric])
+  extends EvalPythonEvaluatorFactory(childOutput, udfs, output) {
+
+  private[python] def runtimeSession: 
InProcessPythonRuntime.InterpreterSession =
+    InProcessPythonRuntime.currentSession
+
+  /** Unused: `evaluateJoined` always evaluates the UDFs. */
+  override protected def evaluate(
+      funcs: Seq[(ChainedPythonFunctions, Long)],
+      argMetas: Array[Array[ArgumentMetadata]],
+      rows: Iterator[InternalRow],
+      inputSchema: StructType,
+      context: TaskContext): Iterator[InternalRow] =
+    throw SparkException.internalError("In-process UDFs are evaluated with 
their input rows")
+
+  override protected def evaluateJoined(
+      funcs: Seq[(ChainedPythonFunctions, Long)],
+      argMetas: Array[Array[ArgumentMetadata]],
+      rows: Iterator[InternalRow],
+      inputs: Seq[Expression],
+      inputSchema: StructType,
+      context: TaskContext): Option[Iterator[InternalRow]] = {
+    import InProcessArrowEvalPythonEvaluatorFactory.{Buffered, ReadBack, 
readsBack}
+    val inputColumns = inputs.length == childOutput.length && 
inputs.zip(childOutput).forall {
+      case (a: Attribute, c) => a.exprId == c.exprId
+      case _ => false
+    }
+    // If all input columns are UDF arguments, they are written to Arrow 
regardless. Read them
+    // back from the exported input vectors instead of buffering every input 
row, if their
+    // values read back from Arrow exactly as written and as fast as an unsafe 
row copy.
+    val joinInput = if (inputColumns && inputSchema.forall(f => 
readsBack(f.dataType))) {
+      ReadBack
+    } else if (inputColumns) {
+      Buffered(None)
+    } else {
+      // Each projected row is written to Arrow before the next input row is 
pulled, so the
+      // arguments go into a reused buffer rather than being copied value by 
value.
+      val projection = UnsafeProjection.create(inputs, childOutput)
+      projection.initialize(context.partitionId())
+      Buffered(Some(projection))
+    }
+    Some(evaluateBatches(funcs, argMetas, rows, inputSchema, context, 
joinInput))
+  }
+
+  private[python] def evaluateBatches(
+      funcs: Seq[(ChainedPythonFunctions, Long)],
+      argMetas: Array[Array[ArgumentMetadata]],
+      rows: Iterator[InternalRow],
+      inputSchema: StructType,
+      context: TaskContext,
+      joinInput: InProcessArrowEvalPythonEvaluatorFactory.JoinInput): 
Iterator[InternalRow] = {
+    import InProcessArrowEvalPythonEvaluatorFactory.{Buffered, ReadBack}
+    ArrowUtils.failDuplicatedFieldNames(inputSchema)
+    val functions = funcs.map { case (chain, _) =>
+      if (chain.funcs.size != 1) {
+        throw SparkException.internalError(
+          "In-process UDF chains must use separate evaluation nodes")
+      }
+      chain.funcs.head
+    }
+    val inputOrdinals = argMetas.map(_.map(_.offset))
+    def checkCancellation(): Unit = context.killTaskIfInterrupted()
+
+    val expectedFields = udfs.map { udf =>
+      ArrowUtils.toArrowField("result", udf.dataType, true, timeZoneId, 
largeVarTypes)
+    }
+    val processingTime = new 
InProcessArrowEvalPythonEvaluatorFactory.NanosecondTimer(
+      metrics("pythonProcessingTime"))
+    val initTime = new 
InProcessArrowEvalPythonEvaluatorFactory.NanosecondTimer(
+      metrics("pythonInitTime"))
+    val arrowSchema = ArrowUtils.toArrowSchema(inputSchema, timeZoneId, 
largeVarTypes)
+    // Capture before consuming input: an old task must never join a later 
context's session.
+    val runtime = runtimeSession
+    // Rows are copied out of the queue and Arrow vectors before they are 
returned, so they
+    // remain valid after task completion releases those, on whichever thread 
consumes them.
+    val resultProj = UnsafeProjection.create(output, output)
+    // Spill files go into a directory of the queue's own, created with the 
first disk queue, so
+    // that task completion can delete them when it cannot close the queue.
+    @volatile var spillDir: File = null
+    // Guarded by the queue's monitor.
+    var queueAbandoned = false
+    val (queue, projection) = joinInput match {
+      case Buffered(projection) =>
+        val localDir = new File(Utils.getLocalDir(SparkEnv.get.conf))
+        val serializerManager = SparkEnv.get.serializerManager
+        // Only the consumer holding the iterator's lock adds and removes rows.
+        val queue = new HybridRowQueue(context.taskMemoryManager(), localDir,
+            childOutput.length, serializerManager, lockFree = true) {
+          override protected def createDiskQueue(): RowQueue = synchronized {
+            if (spillDir == null) {
+              spillDir = Files.createTempDirectory(localDir.toPath, 
"inprocess-udf-").toFile
+            }
+            DiskRowQueue(Files.createTempFile(spillDir.toPath, "buffer", 
"").toFile,
+              childOutput.length, serializerManager)
+          }
+
+          // Once task completion leaves the queue to the executor, it must 
not spill for other
+          // consumers into a directory that nothing deletes.
+          override def spill(size: Long, trigger: MemoryConsumer): Long = 
synchronized {
+            if (queueAbandoned) 0L else super.spill(size, trigger)
+          }
+        }
+        (queue, projection.orNull)
+      case ReadBack => (null, null)
+    }
+    val joined = new JoinedRow
+    val handles = functions.map(_ => UUID.randomUUID().toString)
+    var registered = false
+    var writer: ArrowWriter = null
+    val results = ArrayBuffer.empty[ArrowColumnVector]
+
+    def closeBatch(): Unit = {
+      val resources = ArrayBuffer.empty[AutoCloseable]
+      resources ++= results
+      results.clear()
+      if (writer != null) {
+        resources += writer.root
+        writer = null
+      }
+      AutoCloseables.close(resources.asJava)
+    }
+
+    val resources = new 
InProcessArrowEvalPythonEvaluatorFactory.IteratorResources(
+      // Closing the queue deletes the spill files it tracks; deleteQuietly 
also removes any
+      // other, without starting a process or throwing, also on an interrupted 
thread.
+      releaseTaskMemory = () => if (queue != null) {
+        Utils.tryWithSafeFinally(queue.close())(Utils.deleteQuietly(spillDir))
+      },
+      abandonTaskMemory = () => if (queue != null) {
+        queue.synchronized {
+          queueAbandoned = true
+          Utils.deleteQuietly(spillDir)

Review Comment:
   Done in 8aead4b: the queue is now a local `InProcessRowQueue` whose 
`abandon()` marks it abandoned and, under its monitor, closes the disk queues 
in `queues` and `reading` before it deletes the directory; closing a 
`DiskRowQueue` frees no task memory. The consumer's queue changes are visible 
there, since it marks its read with a volatile write afterwards and the 
listener reads that mark before it abandons. I did not find a test that 
observes the streams on Linux or macOS, where the unlinked files are deleted 
either way; the abandonment tests still check the directory.



##########
python/pyspark/sql/tests/test_inprocess_udf.py:
##########
@@ -0,0 +1,1957 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+"""End-to-end tests for in-process Python UDFs.
+
+Run with python/run-tests like other SQL tests. JEP paths are discovered from 
the
+selected Python environment before the Spark JVM starts. ARROW_C_DATA_JAR must
+point to the provided Arrow CDI JAR. Set INPROCESS_TESTS=1
+to require the suite (missing dependencies then fail), or 0 to disable it.
+Otherwise, the suite runs when JEP, PyArrow and the CDI JAR are available.
+"""
+
+import os
+import shutil
+import tempfile
+import unittest
+import zipfile
+from importlib.util import find_spec
+from pathlib import Path
+from unittest.mock import patch
+
+from pyspark.testing.sqlutils import ReusedSQLTestCase
+from pyspark.testing.utils import eventually
+
+_jep_spec = find_spec("jep")
+_cdi_jar = os.environ.get("ARROW_C_DATA_JAR")
+_test_mode = os.environ.get("INPROCESS_TESTS")
+_run_inprocess = _test_mode == "1" or (
+    _test_mode != "0"
+    and _jep_spec is not None
+    and find_spec("pyarrow") is not None
+    and _cdi_jar is not None
+    and Path(_cdi_jar).is_file()
+)
+
+
[email protected](_run_inprocess, "Requires JEP, PyArrow and 
ARROW_C_DATA_JAR")
+class InProcessUDFTests(ReusedSQLTestCase):
+    """
+    End-to-end tests for @inprocess_udf that require jep + CPython + PyArrow.
+
+    The plugin initializes JEP before any task starts. Calls from task threads 
and
+    shutdown must use the same dedicated interpreter thread.
+    """
+
+    @classmethod
+    def master(cls):
+        return "local[2]"
+
+    @classmethod
+    def conf(cls):
+        return (
+            super()
+            .conf()
+            .set("spark.task.cpus", "0.5")
+            .set("spark.driver.extraClassPath", 
os.pathsep.join([str(cls.jep_jar), cls.cdi_jar]))
+            .set("spark.driver.extraLibraryPath", str(cls.jep_dir))
+            .set(
+                "spark.python.inProcess.sitePackages",
+                ",".join([cls.site_packages, str(cls.jep_dir.parent)]),
+            )
+            .set("spark.plugins", 
"org.apache.spark.sql.execution.python.InProcessPythonPlugin")
+        )
+
+    @classmethod
+    def setUpClass(cls):
+        if _jep_spec is None:
+            raise RuntimeError("INPROCESS_TESTS=1 requires JEP in the selected 
Python environment")
+        # Do not import jep: it can only be imported by an embedded 
interpreter.
+        cls.jep_dir = Path(_jep_spec.origin).parent
+        jars = list(cls.jep_dir.glob("jep-*.jar"))
+        if len(jars) != 1:
+            raise RuntimeError(f"Expected one JEP JAR in {cls.jep_dir}, found 
{len(jars)}")
+        cls.jep_jar = jars[0]
+        if not _cdi_jar or not Path(_cdi_jar).is_file():
+            raise RuntimeError("Set ARROW_C_DATA_JAR to the provided Arrow CDI 
JAR")
+        cls.cdi_jar = str(Path(_cdi_jar).resolve())
+        cls.site_packages = tempfile.mkdtemp()
+        helper_dir = os.path.join(cls.site_packages, "extra")
+        system_dir = os.path.join(cls.site_packages, "system")
+        os.mkdir(helper_dir)
+        os.mkdir(system_dir)
+        with open(os.path.join(system_dir, "_inprocess_process_helper.py"), 
"w") as f:
+            f.write("MAGIC = -1\n")
+        with open(os.path.join(helper_dir, "_inprocess_test_helper.py"), "w") 
as f:
+            f.write("MAGIC = 99\n")
+        with open(os.path.join(cls.site_packages, "helper.pth"), "w") as f:
+            f.write("extra\n")
+        for name in ["spire", "redis"]:
+            package = Path(cls.site_packages) / name
+            package.mkdir()
+            (package / "__init__.py").write_text("PYTHON_PACKAGE = True\n")
+        shadow = os.path.join(cls.site_packages, "pyspark")
+        os.mkdir(shadow)
+        with open(os.path.join(shadow, "__init__.py"), "w") as f:
+            f.write("raise RuntimeError('site-packages must not shadow Spark 
PySpark')\n")
+        try:
+            # CI extracts compiled targets without building pyspark.zip. Keep 
the source
+            # tree available, while still requiring the configured paths to 
provide JEP.
+            cls.python_source = Path(__file__).resolve().parents[3]
+            archive = cls.python_source / "lib" / "pyspark.zip"
+            if archive.is_file():
+                with zipfile.ZipFile(archive) as packaged:
+                    for module in (cls.python_source / "pyspark" / 
"inprocess").glob("*.py"):
+                        name = module.relative_to(cls.python_source).as_posix()
+                        if (
+                            name not in packaged.namelist()
+                            or packaged.read(name) != module.read_bytes()
+                        ):
+                            raise RuntimeError("Rebuild or remove stale 
python/lib/pyspark.zip")
+            python_path = os.pathsep.join([str(cls.python_source), system_dir])
+            with patch.dict(os.environ, {"PYTHONPATH": python_path}):
+                super().setUpClass()
+        except Exception:
+            shutil.rmtree(cls.site_packages)
+            raise
+
+    @classmethod
+    def tearDownClass(cls):
+        try:
+            super().tearDownClass()
+        finally:
+            shutil.rmtree(cls.site_packages)
+
+    def test_driver_defined_udt_return_type(self):
+        import sys
+
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType, UserDefinedType
+
+        class DriverUDT(UserDefinedType):
+            @classmethod
+            def sqlType(cls):
+                return LongType()
+
+            @classmethod
+            def module(cls):
+                return "__main__"
+
+            def serialize(self, value):
+                return value
+
+            def deserialize(self, value):
+                return value
+
+        DriverUDT.__module__ = "__main__"
+        with patch.object(sys.modules["__main__"], "DriverUDT", DriverUDT, 
create=True):
+            identity = inprocess_udf(DriverUDT())(lambda x: x)
+            result = self.spark.range(3).select(identity("id"))
+            self.assertEqual([r[0] for r in result.collect()], [0, 1, 2])
+
+    def test_unsupported_ddl_return_type_fails_on_driver(self):
+        from pyspark.errors import PySparkNotImplementedError
+        from pyspark.inprocess import inprocess_udf
+
+        wrapper = inprocess_udf("interval year to month")(lambda x: x)
+        with self.assertRaises(PySparkNotImplementedError):
+            wrapper("id")
+        self.assertIsNone(wrapper._serialized)
+
+    def test_worker_environment_is_rejected(self):
+        from pyspark.inprocess import inprocess_udf
+
+        identity = inprocess_udf("long")(lambda x: x)
+        column = identity("id")
+        with self.sql_conf({"spark.pythonWorkerEnv.INPROCESS_TEST_VALUE": 
"value"}):
+            # Columns are session-agnostic; validate using the query's session 
at execution.
+            identity("id")
+            with self.assertRaisesRegex(Exception, 
"UNSUPPORTED_IN_PROCESS_PYTHON_UDF"):
+                self.spark.range(1).select(column).collect()
+
+    def test_profiler_and_memory_settings_are_rejected(self):
+        from pyspark.inprocess import inprocess_udf
+
+        identity = inprocess_udf("long")(lambda x: x)
+        column = identity("id")
+        with self.sql_conf({"spark.sql.pyspark.udf.profiler": "perf"}):
+            # Columns are session-agnostic; validate using the query's session 
at execution.
+            identity("id")
+            with self.assertRaisesRegex(Exception, 
"UNSUPPORTED_IN_PROCESS_PYTHON_UDF"):
+                self.spark.range(1).select(column).collect()
+        conf = 
self.spark.sparkContext._jvm.org.apache.spark.SparkEnv.get().conf()
+        key = "spark.executor.pyspark.memory"
+        try:
+            conf.set(key, "128m")
+            # Columns are session-agnostic; validate using the query's session 
at execution.
+            identity("id")
+            with self.assertRaisesRegex(Exception, 
"UNSUPPORTED_IN_PROCESS_PYTHON_UDF"):
+                self.spark.range(1).select(column).collect()
+        finally:
+            conf.remove(key)
+
+    def test_configuration_uses_the_query_session(self):
+        from pyspark.inprocess import inprocess_udf
+
+        identity = inprocess_udf("long")(lambda x: x)
+        second = self.spark.newSession()
+        with self.sql_conf({"spark.sql.pyspark.udf.profiler": "perf"}):
+            column = identity("id")
+            self.assertEqual([r[0] for r in 
second.range(2).select(column).collect()], [0, 1])
+            with self.assertRaisesRegex(Exception, 
"UNSUPPORTED_IN_PROCESS_PYTHON_UDF"):
+                self.spark.range(2).select(column).collect()
+        conf = 
self.spark.sparkContext._jvm.org.apache.spark.SparkEnv.get().conf()
+        try:
+            conf.set("spark.executor.pyspark.memory", "0")
+            
self.assertEqual(self.spark.range(1).select(identity("id")).first()[0], 0)
+        finally:
+            conf.remove("spark.executor.pyspark.memory")
+
+    def test_python_packages_are_not_shadowed_by_java_imports(self):
+        from pyspark.inprocess import inprocess_udf
+
+        def probe(x):
+            import sys
+
+            import pyarrow as pa
+            import redis
+            import spire
+
+            good = spire.PYTHON_PACKAGE and redis.PYTHON_PACKAGE
+            good = good and sys.stdout.line_buffering and 
sys.stdout.write_through
+            return pa.array([good] * len(x))
+
+        self.assertTrue(
+            
self.spark.range(1).select(inprocess_udf("boolean")(probe)("id")).first()[0]
+        )
+
+    def test_result_schema_adapts_to_session_representation(self):
+        from pyspark.inprocess import inprocess_udf
+
+        def timestamp(x):
+            import pyarrow as pa
+
+            return pa.array([0] * len(x), type=pa.timestamp("us", tz="UTC"))
+
+        def nested(x):
+            import pyarrow as pa
+
+            # Declare the field order: newer PyArrow versions sort inferred 
struct fields.
+            return pa.array(
+                [{"s": ["hello"], "b": b"data"}] * len(x),
+                pa.struct([("s", pa.list_(pa.string())), ("b", pa.binary())]),
+            )
+
+        for zone in ["UTC", "Etc/UTC", "America/Los_Angeles"]:
+            with self.sql_conf({"spark.sql.session.timeZone": zone}):
+                result = 
self.spark.range(1).select(inprocess_udf("timestamp")(timestamp)("id"))
+                self.assertEqual(
+                    
result.toDF("value").selectExpr("unix_micros(value)").first()[0], 0
+                )
+        with self.sql_conf({"spark.sql.execution.arrow.useLargeVarTypes": 
"true"}):
+            result = (
+                self.spark.range(1)
+                
.select(inprocess_udf("struct<s:array<string>,b:binary>")(nested)("id"))
+                .first()[0]
+            )
+            self.assertEqual(result.s, ["hello"])
+            self.assertEqual(result.b, b"data")
+
+    def test_kwargs_only_function(self):
+        from pyspark.inprocess import inprocess_udf
+
+        identity = inprocess_udf("long")(lambda **cols: cols["x"])
+        self.assertEqual(
+            [row[0] for row in 
self.spark.range(2).select(identity(x="id")).collect()], [0, 1]
+        )
+
+    def test_isolated_interpreter_and_explicit_process_pythonpath(self):
+        from pyspark.inprocess import inprocess_udf
+
+        def flags(x):
+            import faulthandler
+            import sys
+
+            import _inprocess_process_helper
+            import pyarrow as pa
+
+            value = (
+                sys.flags.isolated == 1
+                and sys.flags.ignore_environment == 1
+                and not faulthandler.is_enabled()
+                and _inprocess_process_helper.MAGIC == -1
+            )
+            return pa.array([value] * len(x))
+
+        self.assertTrue(
+            
self.spark.range(1).select(inprocess_udf("boolean")(flags)("id")).first()[0]
+        )
+
+    def test_missing_cdi_dependency_fails_plugin_startup(self):
+        import subprocess
+
+        jvm = self.spark.sparkContext._jvm
+        java_home = jvm.java.lang.System.getProperty("java.home")
+        classpath = os.pathsep.join(
+            p
+            for p in 
jvm.java.lang.System.getProperty("java.class.path").split(os.pathsep)
+            if p != self.cdi_jar
+        )
+        source = """
+import java.lang.reflect.Proxy;
+import java.util.Collections;
+import org.apache.spark.SparkConf;
+import org.apache.spark.api.plugin.PluginContext;
+import org.apache.spark.sql.execution.python.InProcessPythonPlugin;
+
+class MissingCdiProbe {
+  public static void main(String[] args) {
+    PluginContext context = (PluginContext) Proxy.newProxyInstance(
+        PluginContext.class.getClassLoader(), new Class<?>[] 
{PluginContext.class},
+        (proxy, method, values) -> new SparkConf(false));
+    try {
+      new InProcessPythonPlugin().executorPlugin().init(context, 
Collections.emptyMap());
+      throw new AssertionError("Plugin accepted a missing CDI dependency");
+    } catch (IllegalStateException expected) {
+      if (!(expected.getCause() instanceof NoClassDefFoundError)) throw 
expected;
+      if (!expected.getMessage().contains("arrow-c-data.jar")) throw expected;
+      System.out.println("MISSING_CDI_REJECTED");
+    }
+  }
+}
+"""
+        with tempfile.TemporaryDirectory() as directory:
+            source_file = Path(directory) / "MissingCdiProbe.java"
+            source_file.write_text(source)
+            result = subprocess.run(
+                [str(Path(java_home) / "bin" / "java"), "-cp", classpath, 
str(source_file)],
+                capture_output=True,
+                text=True,
+                timeout=90,
+            )
+            self.assertEqual(result.returncode, 0, result.stdout + 
result.stderr)
+            self.assertIn("MISSING_CDI_REJECTED", result.stdout)
+
+    def test_missing_jep_has_an_initialization_hint(self):
+        import subprocess
+
+        jvm = self.spark.sparkContext._jvm
+        java_home = jvm.java.lang.System.getProperty("java.home")
+        classpath = os.pathsep.join(
+            p
+            for p in 
jvm.java.lang.System.getProperty("java.class.path").split(os.pathsep)
+            if p != str(self.jep_jar)
+        )
+        source = """
+import java.lang.reflect.Proxy;
+import java.util.Collections;
+import org.apache.spark.SparkConf;
+import org.apache.spark.api.plugin.PluginContext;
+import org.apache.spark.sql.execution.python.InProcessPythonPlugin;
+import org.apache.spark.sql.execution.python.InProcessPythonRuntime;
+
+class MissingJepProbe {
+  public static void main(String[] args) {
+    try {
+      InProcessPythonRuntime.currentSession();
+      throw new AssertionError("Uninitialized runtime was accepted");
+    } catch (IllegalStateException expected) {
+      if (!expected.getMessage().contains("executor plugin")) throw expected;
+    }
+    PluginContext context = (PluginContext) Proxy.newProxyInstance(
+        PluginContext.class.getClassLoader(), new Class<?>[] 
{PluginContext.class},
+        (proxy, method, values) -> new SparkConf(false));
+    try {
+      new InProcessPythonPlugin().executorPlugin().init(context, 
Collections.emptyMap());
+      throw new AssertionError("Plugin accepted a missing JEP dependency");
+    } catch (IllegalStateException expected) {
+      if (!(expected.getCause() instanceof LinkageError)) throw expected;
+      if (!expected.getMessage().contains("jep.jar")) throw expected;
+      System.out.println("MISSING_JEP_REJECTED");
+    }
+  }
+}
+"""
+        with tempfile.TemporaryDirectory() as directory:
+            source_file = Path(directory) / "MissingJepProbe.java"
+            source_file.write_text(source)
+            result = subprocess.run(
+                [
+                    str(Path(java_home) / "bin" / "java"),
+                    "--add-opens=java.base/java.nio=ALL-UNNAMED",
+                    "--add-opens=java.base/sun.nio.ch=ALL-UNNAMED",
+                    "-Dio.netty.tryReflectionSetAccessible=true",
+                    "-cp",
+                    classpath,
+                    str(source_file),
+                ],
+                capture_output=True,
+                text=True,
+                timeout=90,
+            )
+            self.assertEqual(result.returncode, 0, result.stdout + 
result.stderr)
+            self.assertIn("MISSING_JEP_REJECTED", result.stdout)
+
+    def test_fresh_jvm_retries_configuration_without_spark_home(self):
+        import subprocess
+        import venv
+
+        from pyspark import cloudpickle
+
+        jvm = self.spark.sparkContext._jvm
+        java_home = jvm.java.lang.System.getProperty("java.home")
+        classpath = jvm.java.lang.System.getProperty("java.class.path")
+        spark_home = jvm.java.lang.System.getenv("SPARK_HOME")
+        self.assertIsNotNone(spark_home)
+        python_lib = Path(spark_home) / "python" / "lib"
+        if not (python_lib / "pyspark.zip").is_file():
+            self.skipTest("Packaged bootstrap coverage requires 
python/lib/pyspark.zip")
+        env = os.environ.copy()
+        env.pop("SPARK_HOME", None)
+        env.pop("VIRTUAL_ENV", None)
+        env["PATH"] = os.defpath
+        env["PYTHONPATH"] = os.pathsep.join(str(p) for p in 
python_lib.glob("*.zip"))
+        # These flags must be ignored by the embedded interpreter. No signals 
are raised.
+        env["PYTHONFAULTHANDLER"] = "1"
+        env["PYTHONDEVMODE"] = "1"
+        env["LC_ALL"] = "C"
+        env["LANG"] = "C"
+
+        class BootstrapCheck:
+            def __reduce__(self):
+                return eval, (
+                    "(__import__('sys').flags.isolated == 1 and "
+                    "__import__('sys').flags.ignore_environment == 1 and "
+                    "not __import__('faulthandler').is_enabled() and "
+                    "'pyspark.zip' in __import__('pyspark').__file__ and "
+                    "__import__('sys').stdout.line_buffering and "
+                    "__import__('sys').stdout.write_through and "
+                    "(print('SHUTDOWN_FLUSH', end='') or (lambda x: x))) or "
+                    "(_ for _ in ()).throw(AssertionError('unexpected 
bootstrap state'))",
+                )
+
+        source = """
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import org.apache.arrow.vector.types.pojo.Field;
+import org.apache.spark.sql.execution.python.InProcessPythonRuntime;
+import org.apache.spark.sql.types.DataTypes;
+import org.apache.spark.sql.util.ArrowUtils;
+
+class BootstrapProbe {
+  public static void main(String[] args) throws Exception {
+    var bad = 
scala.jdk.javaapi.CollectionConverters.asScala(Arrays.asList(args[0])).toSeq();
+    boolean failed = false;
+    try {
+      InProcessPythonRuntime.initialize(bad);
+    } catch (jep.JepException expected) {
+      failed = true;
+    }
+    if (!failed) throw new AssertionError("Expected missing JEP package");
+    var good = scala.jdk.javaapi.CollectionConverters
+        .asScala(Arrays.asList(args[1], args[2])).toSeq();
+    try {
+      InProcessPythonRuntime.initialize(good);
+      Field field = ArrowUtils.toArrowField("result", DataTypes.LongType, 
true, "UTC",
+          false, org.apache.spark.sql.types.Metadata.empty(), false);
+      InProcessPythonRuntime.currentSession().register("probe",
+          Files.readAllBytes(Path.of(args[3])), field, args[4], false, false, 
false, true);
+      if (ArrowUtils.rootAllocator().getAllocatedMemory() != 0) {
+        throw new AssertionError("Unreleased registration schema");
+      }
+      System.out.println("BOOTSTRAP_OK");
+    } finally {
+      InProcessPythonRuntime.currentSession().release(
+          
scala.jdk.javaapi.CollectionConverters.asScala(Arrays.asList("probe")).toSeq());
+      InProcessPythonRuntime.shutdown();
+    }
+  }
+}
+"""
+        with tempfile.TemporaryDirectory() as directory:
+            # Keep JEP absent initially even when it is installed in the 
system Python.
+            clean_python = Path(directory) / "python"
+            venv.EnvBuilder(with_pip=False).create(clean_python)
+            env["PATH"] = str(clean_python / "bin") + os.pathsep + os.defpath
+            source_file = Path(directory) / "BootstrapProbe.java"
+            source_file.write_text(source)
+            command_file = Path(directory) / "command.pickle"
+            command_file.write_bytes(cloudpickle.dumps(BootstrapCheck()))
+            import sys
+
+            result = subprocess.run(
+                [
+                    str(Path(java_home) / "bin" / "java"),
+                    "--add-opens=java.base/java.nio=ALL-UNNAMED",
+                    "--add-opens=java.base/sun.nio.ch=ALL-UNNAMED",
+                    "-Dio.netty.tryReflectionSetAccessible=true",
+                    f"-Djava.library.path={self.jep_dir}",
+                    "--class-path",
+                    classpath,
+                    str(source_file),
+                    directory,
+                    self.site_packages,
+                    str(self.jep_dir.parent),
+                    str(command_file),
+                    "%d.%d" % sys.version_info[:2],
+                ],
+                env=env,
+                capture_output=True,
+                text=True,
+                timeout=90,
+            )
+            self.assertEqual(result.returncode, 0, result.stdout + 
result.stderr)
+            self.assertIn("BOOTSTRAP_OK", result.stdout)
+            self.assertIn("SHUTDOWN_FLUSH", result.stdout)
+            self.assertIn("set LC_ALL=C.UTF-8", result.stderr)
+
+    def 
test_failed_bootstrap_preserves_message_and_freezes_site_packages(self):
+        import subprocess
+
+        jvm = self.spark.sparkContext._jvm
+        java_home = jvm.java.lang.System.getProperty("java.home")
+        classpath = jvm.java.lang.System.getProperty("java.class.path")
+        source = """
+import java.util.Arrays;
+import org.apache.spark.sql.execution.python.InProcessPythonRuntime;
+
+class BootstrapFailureProbe {
+  public static void main(String[] args) {
+    var paths = scala.jdk.javaapi.CollectionConverters
+        .asScala(Arrays.asList(args[0], args[1])).toSeq();
+    try {
+      InProcessPythonRuntime.initialize(paths);
+      throw new AssertionError("Expected an unsupported PyArrow version");
+    } catch (jep.JepException expected) {
+      String message = expected.getMessage();
+      if (!message.contains("PySparkImportError") ||
+          !message.contains("UNSUPPORTED_PACKAGE_VERSION") ||
+          !message.contains("PyArrow") || !message.contains("0.0.0")) throw 
expected;
+    }
+    var changed = scala.jdk.javaapi.CollectionConverters
+        .asScala(Arrays.asList(args[1])).toSeq();
+    try {
+      InProcessPythonRuntime.initialize(changed);
+      throw new AssertionError("Accepted a different environment after 
bootstrap failure");
+    } catch (IllegalStateException expected) {
+      if (!expected.getMessage().contains("Restart the executor process")) 
throw expected;
+    }
+    System.out.println("BOOTSTRAP_FAILURE_CHECKED");
+  }
+}
+"""
+        with tempfile.TemporaryDirectory() as directory:
+            # Use a backslash in a supported POSIX path to exercise JEP's 
escaping too.
+            packages = Path(directory) / "back\\slash"
+            packages.mkdir()
+            (packages / "old_arrow.pth").write_text(
+                "import pyarrow; pyarrow.__version__ = '0.0.0'\n"
+            )
+            source_file = Path(directory) / "BootstrapFailureProbe.java"
+            source_file.write_text(source)
+            env = os.environ.copy()
+            # This direct JVM probe needs no Spark installation and always 
imports source.
+            # Py4J comes from the same place as in this process, e.g. Spark's 
source zip.
+            import py4j
+
+            env["SPARK_HOME"] = directory
+            env["PYTHONPATH"] = os.pathsep.join(
+                [str(self.python_source), str(Path(py4j.__file__).parents[1])]
+            )
+            result = subprocess.run(
+                [
+                    str(Path(java_home) / "bin" / "java"),
+                    f"-Djava.library.path={self.jep_dir}",
+                    "--class-path",
+                    classpath,
+                    str(source_file),
+                    str(packages),
+                    str(self.jep_dir.parent),
+                ],
+                env=env,
+                capture_output=True,
+                text=True,
+                timeout=90,
+            )
+            self.assertEqual(result.returncode, 0, result.stdout + 
result.stderr)
+            self.assertIn("BOOTSTRAP_FAILURE_CHECKED", result.stdout)
+
+    def test_exception_unicode_and_nul_survive_jep(self):
+        from pyspark.inprocess import inprocess_udf
+
+        def fail(x):
+            raise ValueError("failure: caf\u00e9 \u4e2d\u6587 \U0001f600 
\ud800 \0 tail")
+
+        with self.assertRaises(Exception) as error:
+            
self.spark.range(1).select(inprocess_udf("long")(fail)("id")).collect()
+        self.assertIn("caf\u00e9 \u4e2d\u6587", str(error.exception))
+        self.assertIn(r"\U0001f600 \ud800 \x00 tail", str(error.exception))
+
+    def test_named_argument_resolver(self):
+        from pyspark.inprocess import inprocess_udf
+
+        identity = inprocess_udf("long")(lambda x, **kw: x)
+        with self.sql_conf({"spark.sql.caseSensitive": "false"}):
+            with self.assertRaisesRegex(Exception, 
"DOUBLE_NAMED_ARGUMENT_REFERENCE"):
+                identity(x="id", X="id")
+        with self.sql_conf({"spark.sql.caseSensitive": "true"}):
+            result = self.spark.range(2).select(identity(x="id", X="id"))
+            self.assertEqual([r[0] for r in result.collect()], [0, 1])
+
+    def test_spark_python_distribution_precedes_site_packages(self):
+        import pyarrow as pa
+
+        from pyspark.inprocess import inprocess_udf
+
+        def location(x):
+            import pyspark
+
+            return pa.array([pyspark.__file__] * len(x))
+
+        path = 
self.spark.range(1).select(inprocess_udf("string")(location)("id")).first()[0]
+        expected = str(self.python_source / "pyspark" / "__init__.py")
+        packaged = str(self.python_source / "lib" / "pyspark.zip" / "pyspark" 
/ "__init__.py")
+        self.assertIn(path, [expected, packaged])
+
+    def test_declared_struct_metadata(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType, StructField, StructType
+
+        declared = StructType([StructField("x", LongType(), 
metadata={"comment": "c"})])
+        identity = inprocess_udf(declared)(lambda x: x)
+        df = self.spark.sql("SELECT named_struct('x', 7L) AS value")
+        result = df.select(identity("value").alias("value"))
+        self.assertEqual(result.collect(), df.collect())
+        self.assertEqual(result.schema[0].dataType, declared)
+
+    def test_temporal_precision_metadata(self):
+        from pyspark.inprocess import inprocess_udf
+
+        for declared in ["time(3)", "timestamp_ntz(7)", "timestamp_ltz(8)"]:
+            literal = "12:34:56.123" if declared.startswith("time(") else 
"2024-01-02 12:34:56.123"
+            for nested in [False, True]:
+                with self.subTest(declared=declared, nested=nested):
+                    df = self.spark.sql(f"SELECT CAST('{literal}' AS 
{declared}) AS value")
+                    if nested:
+                        df = df.selectExpr("named_struct('t', value) AS value")
+                    identity = inprocess_udf(df.schema[0].dataType)(lambda x: 
x)
+                    result = df.select(identity("value").alias("value"))
+                    self.assertEqual(result.schema[0].dataType, 
df.schema[0].dataType)
+                    self.assertEqual(
+                        result.selectExpr("CAST(value AS STRING)").collect(),
+                        df.selectExpr("CAST(value AS STRING)").collect(),
+                    )
+
+    def test_large_types_variant_and_spatial_identity(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import Geography, GeographyType, Geometry, 
GeometryType
+
+        wkb = bytes.fromhex("010100000000000000000031400000000000001c40")
+        frames = [
+            self.spark.sql("SELECT parse_json('{\"a\":1}') AS value"),
+            self.spark.createDataFrame([(Geometry(wkb, 0),)], "value 
geometry(0)"),
+            self.spark.createDataFrame([(Geography(wkb, 4326),)], "value 
geography(4326)"),
+        ]
+        for large in ["false", "true"]:
+            with self.sql_conf({"spark.sql.execution.arrow.useLargeVarTypes": 
large}):
+                for df in frames:
+                    with self.subTest(large=large, 
data_type=df.schema[0].dataType):
+                        identity = inprocess_udf(df.schema[0].dataType)(lambda 
x: x)
+                        result = df.select(identity("value").alias("value"))
+                        if isinstance(df.schema[0].dataType, (GeometryType, 
GeographyType)):
+                            self.assertEqual(result.collect(), df.collect())
+                        else:
+                            self.assertEqual(
+                                result.selectExpr("CAST(value AS 
STRING)").collect(),
+                                df.selectExpr("CAST(value AS 
STRING)").collect(),
+                            )
+
+    def test_ddl_return_type_and_nondeterminism(self):
+        from pyspark.inprocess import inprocess_udf
+
+        identity = inprocess_udf("long")(lambda x: x).asNondeterministic()
+        
self.assertEqual(self.spark.range(2).select(identity("id")).first()[0], 0)
+        plan = 
self.spark.range(1).select(identity("id"))._jdf.queryExecution().analyzed()
+        self.assertFalse(plan.expressions().apply(0).deterministic())
+
+    def test_calls_share_one_jvm_function(self):
+        import copy
+
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess import inprocess_udf
+
+        jvm = self.spark._jvm
+        double = inprocess_udf("long")(lambda x: pc.multiply(x, 2))
+
+        def functions(*cols):
+            plan = 
self.spark.range(1).select(*cols)._jdf.queryExecution().analyzed()
+            udfs = [plan.expressions().apply(i).child() for i in 
range(len(cols))]
+            return [jvm.System.identityHashCode(udf.func()) for udf in udfs], 
udfs
+
+        # The command crosses py4j once, however many expressions call the UDF.
+        ids, _ = functions(double("id"), double("id"))
+        self.assertEqual(ids[0], ids[1])
+        # Nondeterminism belongs to each call, so it keeps the function.
+        double.asNondeterministic()
+        later, udfs = functions(double("id"))
+        self.assertEqual(later[0], ids[0])
+        self.assertFalse(udfs[0].udfDeterministic())
+        # A called wrapper can still be copied; the copy creates its own 
function.
+        copied = copy.deepcopy(double)
+        self.assertIsNone(copied._jfunc)
+        self.assertIsNone(copied._serialized)
+        
self.assertEqual(self.spark.range(2).select(copied("id")).collect()[1][0], 2)
+
+    def test_traceback_settings_are_per_registration(self):
+        from pyspark.inprocess import inprocess_udf
+
+        # User frames must be outside the pyspark package for the worker's 
simplifier.
+        namespace = {}
+        exec(
+            "def probe(x):\n    probe_local = 8675309\n"
+            "    raise ValueError('traceback policy probe')",
+            namespace,
+        )
+        traceback_probe = inprocess_udf("long")(namespace["probe"])
+
+        for hide, simplified, locals_enabled in [
+            (True, False, False),
+            (False, True, False),
+            (False, False, False),
+            (True, True, True),
+            (False, True, True),
+            (False, False, True),
+        ]:
+            with self.sql_conf(
+                {
+                    
"spark.sql.execution.pyspark.udf.tracebackWithLocals.enabled": str(
+                        locals_enabled
+                    ).lower(),
+                    "spark.sql.execution.pyspark.udf.hideTraceback.enabled": 
str(hide).lower(),
+                    
"spark.sql.execution.pyspark.udf.simplifiedTraceback.enabled": str(
+                        simplified
+                    ).lower(),
+                }
+            ):
+                with self.assertRaises(Exception) as error:
+                    self.spark.range(1).select(traceback_probe("id")).collect()
+                message = str(error.exception)
+                self.assertIn("ValueError: traceback policy probe", message)
+                self.assertEqual('File "' in message, not hide)
+                self.assertEqual("probe_local = 8675309" in message, 
locals_enabled and not hide)
+                if not hide:
+                    self.assertEqual("inprocess/runtime.py" in message, not 
simplified)
+
+    def test_embedded_hash_seed_matches_default_worker_seed(self):
+        import subprocess
+        import sys
+
+        import pyarrow as pa
+
+        from pyspark.inprocess import inprocess_udf
+
+        expected = int(
+            subprocess.check_output(
+                [sys.executable, "-c", "print(hash('spark'))"],
+                env={**os.environ, "PYTHONHASHSEED": "0"},
+            )
+        )
+        hash_udf = inprocess_udf("long")(
+            lambda x: pa.array([hash("spark")] * len(x), type=pa.int64())
+        )
+        rows = self.spark.range(4, 
numPartitions=2).select(hash_udf("id")).collect()
+        self.assertEqual([row[0] for row in rows], [expected] * 4)
+
+    def test_expression_arguments_and_multiple_batches(self):
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.functions import lit
+        from pyspark.sql.types import LongType
+
+        add = inprocess_udf(LongType())(lambda x, y: pc.add(x, y))
+        with self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": 
"2"}):
+            df = self.spark.range(11, numPartitions=3)
+            values = df.select(add(df.id + 1, lit(2).cast("long"))).collect()
+            self.assertEqual([r[0] for r in values], list(range(3, 14)))
+
+    def test_preserved_child_columns_produce_collectable_rows(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        identity = inprocess_udf(LongType())(lambda x: x)
+        df = self.spark.range(3)
+        rows = df.select(df.id, identity(df.id)).collect()
+        self.assertEqual([tuple(r) for r in rows], [(0, 0), (1, 1), (2, 2)])
+
+    def test_unlimited_batch_size(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        identity = inprocess_udf(LongType())(lambda x: x)
+        for batch_size in (0, -1):
+            with (
+                self.subTest(batch_size=batch_size),
+                self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": 
str(batch_size)}),
+            ):
+                df = self.spark.range(5)
+                values = [r[0] for r in df.select(identity(df.id)).collect()]
+                self.assertEqual(values, list(range(5)))
+
+    def test_byte_limit_applies_without_a_row_limit(self):
+        import pyarrow as pa
+
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        lengths = inprocess_udf(LongType())(lambda x: pa.array([len(x)] * 
len(x), type=pa.int64()))
+        with self.sql_conf(
+            {
+                "spark.sql.execution.arrow.maxRecordsPerBatch": "0",
+                "spark.sql.execution.arrow.maxBytesPerBatch": "1",
+            }
+        ):
+            df = self.spark.range(4)
+            self.assertEqual([r[0] for r in 
df.select(lengths(df.id)).collect()], [1] * 4)
+
+    def test_wrong_result_length_fails_before_rows_are_read(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        short = inprocess_udf(LongType())(lambda x: x.slice(0, len(x) - 1))
+        df = self.spark.range(3, numPartitions=1)
+        with self.assertRaisesRegex(Exception, "returned 2 rows; expected 3"):
+            df.select(short(df.id)).collect()
+
+    def test_numpy_finalizers_run_on_the_interpreter_thread(self):
+        from pyspark.inprocess import inprocess_udf
+
+        with tempfile.TemporaryDirectory() as directory:
+            marker = str(Path(directory) / "finalizers.txt")
+
+            def produce(x):
+                import threading
+                import weakref
+
+                import numpy as np
+                import pyarrow as pa
+
+                owner = threading.get_ident()
+
+                def finalized():
+                    with open(marker, "a") as stream:
+                        stream.write(f"{owner} {threading.get_ident()}\n")
+
+                values = np.arange(len(x), dtype=np.int64)
+                weakref.finalize(values, finalized)
+                return pa.array(values)
+
+            with 
self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": "2"}):
+                result = (
+                    self.spark.range(8, numPartitions=2)
+                    .select(inprocess_udf("long")(produce)("id"))
+                    .collect()
+                )
+                self.assertEqual(len(result), 8)
+            # A subsequent invocation waits behind cleanup already queued by 
completed tasks.
+            identity = inprocess_udf("long")(lambda x: x)
+            self.spark.range(1).select(identity("id")).collect()
+            records = Path(marker).read_text().splitlines()
+            self.assertEqual(len(records), 4)
+            for record in records:
+                owner, finalizer = record.split()
+                self.assertEqual(owner, finalizer)
+
+    def test_arrow_memory_is_released_on_success_limit_and_failure(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        identity = inprocess_udf(LongType())(lambda x: x)
+
+        @inprocess_udf(LongType())
+        def fail(x):
+            raise ValueError("second UDF failed")
+
+        arrow_utils = 
self.spark.sparkContext._jvm.org.apache.spark.sql.util.ArrowUtils
+        allocator = arrow_utils.rootAllocator()
+        before = allocator.getAllocatedMemory()
+
+        # The interpreter thread releases Python's references after the query 
returns, and a
+        # failed job does not wait for its other tasks to release their memory.
+        @eventually(timeout=30.0, catch_assertions=True)
+        def assert_released():
+            self.assertEqual(allocator.getAllocatedMemory(), before)
+
+        with self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": 
"2"}):
+            df = self.spark.range(9, numPartitions=3)
+            for _ in range(3):
+                self.assertEqual(df.select(identity(df.id)).collect()[0][0], 0)
+                assert_released()
+            # The filter keeps the limit above the in-process node, which then 
stops early.
+            df.select(identity(df.id).alias("v")).filter("v >= 
0").limit(1).collect()
+            assert_released()
+            with self.assertRaisesRegex(Exception, "second UDF failed"):
+                df.select(identity(df.id), fail(df.id)).collect()
+            assert_released()
+            # Deserialization fails before Python imports any input CDI 
structures.
+            broken = inprocess_udf(LongType())(lambda x: x)
+            broken._serialized = b"invalid pickle"
+            with self.assertRaisesRegex(Exception, "UnpicklingError"):
+                df.select(broken(df.id)).collect()
+            assert_released()
+
+    def test_double_long(self):
+        """@inprocess_udf with LongType input/output doubles each value."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        @inprocess_udf(returnType=LongType())
+        def double(x):
+            return pc.multiply(x, 2)
+
+        df = self.spark.range(1, 6)  # [1, 2, 3, 4, 5]
+        result = df.select(double(df["id"])).collect()
+        self.assertEqual([r[0] for r in result], [2, 4, 6, 8, 10])
+
+    def test_negate_double(self):
+        """@inprocess_udf with DoubleType negates each value."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import DoubleType
+
+        @inprocess_udf(returnType=DoubleType())
+        def negate(x):
+            return pc.negate(x)
+
+        data = [(1.5,), (2.5,), (3.0,)]
+        df = self.spark.createDataFrame(data, ["v"])
+        result = [r[0] for r in df.select(negate(df["v"])).collect()]
+        self.assertAlmostEqual(result[0], -1.5)
+        self.assertAlmostEqual(result[1], -2.5)
+        self.assertAlmostEqual(result[2], -3.0)
+
+    def test_identity_integer(self):
+        """@inprocess_udf with IntegerType passes values through unchanged."""
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import IntegerType
+
+        @inprocess_udf(returnType=IntegerType())
+        def identity(x):
+            return x
+
+        data = [(i,) for i in range(5)]
+        df = self.spark.createDataFrame(data, "v int")
+        result = [r[0] for r in df.select(identity(df["v"])).collect()]
+        self.assertEqual(result, list(range(5)))
+
+    def test_boolean_not(self):
+        """@inprocess_udf with BooleanType inverts each boolean."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import BooleanType
+
+        @inprocess_udf(returnType=BooleanType())
+        def invert(x):
+            return pc.invert(x)
+
+        data = [(True,), (False,), (True,)]
+        df = self.spark.createDataFrame(data, ["v"])
+        result = [r[0] for r in df.select(invert(df["v"])).collect()]
+        self.assertEqual(result, [False, True, False])
+
+    # ------------------------------------------------------------------
+    # Null handling
+    # ------------------------------------------------------------------
+
+    def test_null_passthrough(self):
+        """Null values in the input must produce null in the output."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        @inprocess_udf(returnType=LongType())
+        def negate(x):
+            return pc.negate(x)
+
+        data = [1, None, 3]
+        df = self.spark.createDataFrame([(v,) for v in data], ["v"])
+        rows = df.select(negate(df["v"])).collect()
+
+        self.assertEqual(rows[0][0], -1)
+        self.assertIsNone(rows[1][0])
+        self.assertEqual(rows[2][0], -3)
+
+    def test_all_nulls(self):
+        """Column of all-null values: every output row must be null."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType, StructField, StructType
+
+        @inprocess_udf(returnType=LongType())
+        def double(x):
+            return pc.multiply(x, 2)
+
+        schema = StructType([StructField("v", LongType(), nullable=True)])
+        data = [(None,), (None,), (None,)]
+        df = self.spark.createDataFrame(data, schema)
+        rows = df.select(double(df["v"])).collect()
+
+        for row in rows:
+            self.assertIsNone(row[0])
+
+    # ------------------------------------------------------------------
+    # Multi-column UDFs
+    # ------------------------------------------------------------------
+
+    def test_two_column_add(self):
+        """UDF that adds two LongType columns together."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        @inprocess_udf(returnType=LongType())
+        def add(a, b):
+            return pc.add(a, b)
+
+        data = [(1, 10), (2, 20), (3, 30)]
+        df = self.spark.createDataFrame(data, ["a", "b"])
+        result = [r[0] for r in df.select(add(df["a"], df["b"])).collect()]
+        self.assertEqual(result, [11, 22, 33])
+
+    def test_two_column_multiply(self):
+        """UDF that multiplies two DoubleType columns."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import DoubleType
+
+        @inprocess_udf(returnType=DoubleType())
+        def multiply(a, b):
+            return pc.multiply(a, b)
+
+        data = [(2.0, 3.0), (4.0, 5.0)]
+        df = self.spark.createDataFrame(data, ["a", "b"])
+        result = [r[0] for r in df.select(multiply(df["a"], 
df["b"])).collect()]
+        self.assertAlmostEqual(result[0], 6.0)
+        self.assertAlmostEqual(result[1], 20.0)
+
+    # ------------------------------------------------------------------
+    # UDF reuse and multiple UDFs on the same query
+    # ------------------------------------------------------------------
+
+    def test_two_udfs_same_select(self):
+        """Two different @inprocess_udf calls in the same select are both 
executed."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        @inprocess_udf(returnType=LongType())
+        def double(x):
+            return pc.multiply(x, 2)
+
+        @inprocess_udf(returnType=LongType())
+        def triple(x):
+            return pc.multiply(x, 3)
+
+        df = self.spark.range(1, 4)  # [1, 2, 3]
+        rows = df.select(double(df["id"]), triple(df["id"])).collect()
+        self.assertEqual([r[0] for r in rows], [2, 4, 6])
+        self.assertEqual([r[1] for r in rows], [3, 6, 9])
+
+    def test_udf_reuse_across_queries(self):
+        """The same InProcessUDFWrapper can be applied to different 
DataFrames."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        @inprocess_udf(returnType=LongType())
+        def double(x):
+            return pc.multiply(x, 2)
+
+        df1 = self.spark.range(1, 4)
+        df2 = self.spark.range(10, 13)
+
+        result1 = [r[0] for r in df1.select(double(df1["id"])).collect()]
+        result2 = [r[0] for r in df2.select(double(df2["id"])).collect()]
+
+        self.assertEqual(result1, [2, 4, 6])
+        self.assertEqual(result2, [20, 22, 24])
+
+    # ------------------------------------------------------------------
+    # Concurrency
+    # ------------------------------------------------------------------
+
+    def test_concurrent_tasks_have_separate_function_state(self):
+        import pyarrow as pa
+
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        state = []
+
+        @inprocess_udf(LongType(), deterministic=False)
+        def counter(x):
+            state.append(1)
+            return pa.array([len(state)] * len(x), type=pa.int64())
+
+        with self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": 
"2"}):
+            df = self.spark.range(8, numPartitions=2)
+            for _ in range(2):
+                self.assertEqual(
+                    [r[0] for r in df.select(counter(df.id)).collect()],
+                    [1, 1, 2, 2, 1, 1, 2, 2],
+                )
+
+    # ------------------------------------------------------------------
+    # Closure capture
+    # ------------------------------------------------------------------
+
+    def test_udf_captures_closure(self):
+        """UDF closure values defined in outer scope are serialized 
correctly."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        factor = 7  # captured in closure
+
+        @inprocess_udf(returnType=LongType())
+        def scale(x):
+            return pc.multiply(x, factor)
+
+        df = self.spark.range(1, 4)
+        result = [r[0] for r in df.select(scale(df["id"])).collect()]
+        self.assertEqual(result, [7, 14, 21])
+
+    # ------------------------------------------------------------------
+    # Non-deterministic flag
+    # ------------------------------------------------------------------
+
+    def test_nondeterministic_udf_executes(self):
+        """A UDF declared deterministic=False executes and returns correct 
values."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        @inprocess_udf(returnType=LongType(), deterministic=False)
+        def double(x):
+            return pc.multiply(x, 2)
+
+        df = self.spark.range(1, 4)
+        result = [r[0] for r in df.select(double(df["id"])).collect()]
+        self.assertEqual(result, [2, 4, 6])
+
+    def test_nondeterministic_flag_propagates_to_expression(self):
+        """deterministic=False must be reflected in the PythonUDF 
expression."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        @inprocess_udf(returnType=LongType(), deterministic=False)
+        def double(x):
+            return pc.multiply(x, 2)
+
+        df = self.spark.range(3)
+        jdf = df.select(double(df["id"]))._jdf
+        # Python UDF extraction happens during optimization.
+        optimized = jdf.queryExecution().optimizedPlan()
+
+        # Walk the logical plan via children() (no PartialFunction needed)
+        # to locate the ArrowEvalPython node inserted during optimization.
+        def find_node(plan):
+            if plan.getClass().getSimpleName() == "ArrowEvalPython":
+                return plan
+            children = plan.children().toList()
+            for i in range(children.length()):
+                found = find_node(children.apply(i))
+                if found is not None:
+                    return found
+            return None
+
+        inprocess_node = find_node(optimized)
+        self.assertIsNotNone(inprocess_node, "ArrowEvalPython not found in 
analyzed plan")
+        udfs = inprocess_node.udfs().toList()
+        self.assertGreater(udfs.length(), 0)
+        self.assertFalse(
+            udfs.apply(0).deterministic(),
+            "PythonUDF with deterministic=False must have 
deterministic()==False",
+        )
+
+    # ------------------------------------------------------------------
+    # String type
+    # ------------------------------------------------------------------
+
+    def test_string_identity(self):
+        """@inprocess_udf with StringType passes strings through unchanged."""
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import StringType
+
+        @inprocess_udf(returnType=StringType())
+        def identity(s):
+            return s
+
+        data = [("hello",), ("world",), (None,)]
+        df = self.spark.createDataFrame(data, ["v"])
+        result = [r[0] for r in df.select(identity(df["v"])).collect()]
+        self.assertEqual(result[0], "hello")
+        self.assertEqual(result[1], "world")
+        self.assertIsNone(result[2])
+
+    def test_string_upper(self):
+        """@inprocess_udf with StringType applies utf8_upper transformation."""
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import StringType
+
+        @inprocess_udf(returnType=StringType())
+        def upper(s):
+            return pc.utf8_upper(s)
+
+        data = [("hello",), ("world",)]
+        df = self.spark.createDataFrame(data, ["v"])
+        result = [r[0] for r in df.select(upper(df["v"])).collect()]
+        self.assertEqual(result, ["HELLO", "WORLD"])
+
+    # ------------------------------------------------------------------
+    # Binary type
+    # ------------------------------------------------------------------
+
+    def test_binary_identity(self):
+        """@inprocess_udf with BinaryType passes bytes through unchanged."""
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import BinaryType
+
+        @inprocess_udf(returnType=BinaryType())
+        def identity(b):
+            return b
+
+        data = [(b"hello",), (b"world",), (None,)]
+        df = self.spark.createDataFrame(data, ["v"])
+        result = [r[0] for r in df.select(identity(df["v"])).collect()]
+        self.assertEqual(bytes(result[0]), b"hello")
+        self.assertEqual(bytes(result[1]), b"world")
+        self.assertIsNone(result[2])
+
+    # ------------------------------------------------------------------
+    # Array type
+    # ------------------------------------------------------------------
+
+    def test_array_identity(self):
+        """@inprocess_udf with ArrayType(LongType()) passes arrays through 
unchanged."""
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import ArrayType, LongType
+
+        @inprocess_udf(returnType=ArrayType(LongType()))
+        def identity(arr):
+            return arr
+
+        data = [([1, 2, 3],), ([4, 5],), (None,)]
+        df = self.spark.createDataFrame(data, ["v"])
+        result = [r[0] for r in df.select(identity(df["v"])).collect()]
+        self.assertEqual(list(result[0]), [1, 2, 3])
+        self.assertEqual(list(result[1]), [4, 5])
+        self.assertIsNone(result[2])
+
+    # ------------------------------------------------------------------
+    # Struct type
+    # ------------------------------------------------------------------
+
+    def test_struct_identity(self):
+        """@inprocess_udf with StructType passes structs through unchanged."""
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import DoubleType, LongType, StructField, 
StructType
+
+        inner = StructType([StructField("a", LongType()), StructField("b", 
DoubleType())])
+        outer = StructType([StructField("v", inner)])
+
+        @inprocess_udf(returnType=inner)
+        def identity(s):
+            return s
+
+        data = [((1, 2.0),), ((3, 4.0),)]
+        df = self.spark.createDataFrame(data, outer)
+        result = [r[0] for r in df.select(identity(df["v"])).collect()]
+        self.assertEqual(result[0]["a"], 1)
+        self.assertAlmostEqual(result[0]["b"], 2.0)
+        self.assertEqual(result[1]["a"], 3)
+        self.assertAlmostEqual(result[1]["b"], 4.0)
+
+    # ------------------------------------------------------------------
+    # Date type
+    # ------------------------------------------------------------------
+
+    def test_date_identity(self):
+        """@inprocess_udf with DateType passes dates through unchanged."""
+        import datetime
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import DateType
+
+        @inprocess_udf(returnType=DateType())
+        def identity(d):
+            return d
+
+        dates = [datetime.date(2024, 1, 1), datetime.date(2024, 6, 15), None]
+        data = [(d,) for d in dates]
+        df = self.spark.createDataFrame(data, ["v"])
+        result = [r[0] for r in df.select(identity(df["v"])).collect()]
+        self.assertEqual(result[0], datetime.date(2024, 1, 1))
+        self.assertEqual(result[1], datetime.date(2024, 6, 15))
+        self.assertIsNone(result[2])
+
+    # ------------------------------------------------------------------
+    # Timestamp type
+    # ------------------------------------------------------------------
+
+    def test_timestamp_identity(self):
+        """@inprocess_udf with TimestampType passes timestamps through 
unchanged."""
+        import datetime
+
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import TimestampType
+
+        @inprocess_udf(returnType=TimestampType())
+        def identity(ts):
+            return ts
+
+        data = [(datetime.datetime(2024, 3, 15, 10, 30, 0),), (None,)]
+        df = self.spark.createDataFrame(data, ["v"])
+        result = [r[0] for r in df.select(identity(df["v"])).collect()]
+        self.assertIsNone(result[1])
+        # Check date components are preserved (timezone handling may shift 
hours)
+        self.assertEqual(result[0].year, 2024)
+        self.assertEqual(result[0].month, 3)
+        self.assertEqual(result[0].day, 15)
+
+    # ------------------------------------------------------------------
+    # sitePackages / sys.path extension
+    # ------------------------------------------------------------------
+
+    def test_site_packages_path_extension_works_in_interpreter(self):
+        """The plugin's actual sitePackages config exposes a module to the 
interpreter."""
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        @inprocess_udf(LongType())
+        def read_magic(x):
+            import _inprocess_test_helper
+            import pyarrow as pa
+
+            return pa.array([_inprocess_test_helper.MAGIC] * len(x), 
type=pa.int64())
+
+        df = self.spark.range(1)
+        self.assertEqual(df.select(read_magic(df.id)).first()[0], 99)
+
+    def 
test_bootstrap_converts_base_exceptions_and_retries_the_same_configuration(self):
+        jvm = self.spark.sparkContext._jvm
+        runtime = 
jvm.org.apache.spark.sql.execution.python.InProcessPythonRuntime
+        runtime_module = getattr(
+            getattr(jvm.org.apache.spark.sql.execution.python, 
"InProcessPythonRuntime$"), "MODULE$"
+        )
+
+        def initialize():
+            paths = jvm.java.util.ArrayList()
+            paths.add(self.site_packages)
+            paths.add(str(self.jep_dir.parent))
+            runtime.initialize(jvm.PythonUtils.toSeq(paths))
+
+        # Check the shared guard independently of CPython/JEP exception 
handling.
+        for script in [
+            "raise KeyboardInterrupt('bootstrap probe')",
+            "import missing_bootstrap_probe",
+        ]:
+            with self.assertRaisesRegex(RuntimeError, "bootstrap failed"):
+                exec(runtime_module.bootstrapScript(script), {})
+        runtime.shutdown()
+        probe = Path(self.site_packages) / "probe.pth"
+        try:
+            probe.write_text("import sys; raise KeyboardInterrupt('bootstrap 
probe')\n")
+            with self.assertRaisesRegex(Exception, "bootstrap 
failed.*bootstrap probe"):
+                initialize()
+        finally:
+            probe.unlink()
+            initialize()
+        from pyspark.inprocess import inprocess_udf
+
+        identity = inprocess_udf("long")(lambda x: x)
+        
self.assertEqual(self.spark.range(1).select(identity("id")).first()[0], 0)
+
+    def test_runtime_restart_from_driver_thread(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        identity = inprocess_udf(LongType())(lambda x: x)
+        df = self.spark.range(3)
+        expected = df.select(identity(df.id)).collect()
+        runtime = 
self.spark.sparkContext._jvm.org.apache.spark.sql.execution.python
+        runtime.InProcessPythonRuntime.shutdown()
+        try:
+            with self.assertRaisesRegex(Exception, "has been stopped"):
+                df.select(identity(df.id)).collect()
+            changed = self.spark.sparkContext._jvm.java.util.ArrayList()
+            changed.add(self.site_packages)
+            with self.assertRaisesRegex(Exception, "Restart the executor 
process"):
+                runtime.InProcessPythonRuntime.initialize(
+                    self.spark.sparkContext._jvm.PythonUtils.toSeq(changed)
+                )
+        finally:
+            paths = self.spark.sparkContext._jvm.java.util.ArrayList()
+            paths.add(self.site_packages)
+            paths.add(str(self.jep_dir.parent))
+            runtime.InProcessPythonRuntime.initialize(
+                self.spark.sparkContext._jvm.PythonUtils.toSeq(paths)
+            )
+        self.assertEqual(df.select(identity(df.id)).collect(), expected)
+
+    # ------------------------------------------------------------------
+    # Error handling
+    # ------------------------------------------------------------------
+
+    def test_buggy_udf_exposes_python_traceback(self):
+        """A UDF that raises an exception must include the Python traceback in 
the error.
+
+        The traceback must name the exception type, the error message, and the
+        file/line where the exception was raised, matching what you would see 
in a
+        standard Python traceback.
+        """
+        from pyspark.inprocess.udf import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        @inprocess_udf(returnType=LongType())
+        def always_fails(x):
+            raise ValueError("intentional test error from always_fails")
+
+        df = self.spark.range(1)
+        try:
+            df.select(always_fails(df["id"])).collect()
+            self.fail("Expected exception was not raised")
+        except Exception as e:
+            error_msg = str(e)
+            self.assertIn(
+                "ValueError", error_msg, "Exception type must appear in the 
error message"
+            )
+            self.assertIn(
+                "intentional test error from always_fails",
+                error_msg,
+                "Exception message must appear in the error",
+            )
+            self.assertIn(
+                "always_fails", error_msg, "UDF function name must appear in 
the traceback"
+            )
+
+    def test_sliced_results_are_read_correctly_by_arrow_java(self):
+        import pyarrow as pa
+
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import (
+            ArrayType,
+            BooleanType,
+            LongType,
+            StringType,
+            StructField,
+            StructType,
+        )
+
+        cases = [
+            (pa.array([9, 1, None, 3]).slice(1), LongType()),
+            (pa.array([False, True, None, False]).slice(1), BooleanType()),
+            (pa.array(["discard", "one", None, "three"]).slice(1), 
StringType()),
+            (pa.array([[9], [1], None, [3]]).slice(1), ArrayType(LongType())),
+            (
+                pa.StructArray.from_arrays([pa.array([9, 1, None, 
3]).slice(1)], names=["x"]),
+                StructType([StructField("x", LongType())]),
+            ),
+        ]
+        df = self.spark.range(3, numPartitions=1)
+        for value, return_type in cases:
+            with self.subTest(return_type=return_type):
+                identity = inprocess_udf(return_type)(lambda x: value)
+                actual = [r[0] for r in df.select(identity(df.id)).collect()]
+                if isinstance(return_type, StructType):
+                    actual = [r.asDict() for r in actual]
+                self.assertEqual(actual, value.to_pylist())
+
+    def test_retained_inputs_are_not_overwritten_by_later_batches(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        retained = []
+
+        @inprocess_udf(LongType(), deterministic=False)
+        def remember(x):
+            for previous, snapshot in retained:
+                if previous.to_pylist() != snapshot:
+                    raise ValueError("retained input changed")
+            retained.append((x, x.to_pylist()))
+            return x
+
+        df = self.spark.createDataFrame([(1,), (None,), (3,), (4,), (None,), 
(6,)], "x long")
+        df = df.coalesce(1)
+        with self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": 
"2"}):
+            self.assertEqual(
+                [r[0] for r in df.select(remember("x")).collect()], [1, None, 
3, 4, None, 6]
+            )
+
+    def test_pass_through_struct_with_duplicate_names(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql import functions as F
+        from pyspark.sql.types import LongType
+
+        identity = inprocess_udf(LongType())(lambda x: x)
+        df = self.spark.range(3).select(
+            "id", F.struct(F.col("id"), 
F.col("id").cast("string").alias("id")).alias("s")
+        )
+        # Materialize the struct so CollapseProject cannot move it above the 
UDF.
+        df.cache()
+        try:
+            rows = df.select("s", identity("id")).collect()
+            self.assertEqual(
+                [(tuple(r[0]), r[1]) for r in rows], [((i, str(i)), i) for i 
in range(3)]
+            )
+        finally:
+            df.unpersist()
+
+    def test_pass_through_interval_does_not_require_arrow_conversion(self):
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.types import LongType
+
+        identity = inprocess_udf(LongType())(lambda x: x)
+        df = self.spark.range(3).selectExpr(
+            "id", "make_interval(0, 0, 0, 0, 0, 0, 10000000000 + id) AS c"
+        )
+        df.cache()
+        try:
+            # CalendarInterval cannot be converted to a Python Row. Compare 
JVM Row values.
+            expected = df.select("c", "id")._jdf.collect()
+            actual = df.select("c", identity("id"))._jdf.collect()
+            self.assertEqual(
+                [(r.get(0).toString(), r.getLong(1)) for r in actual],
+                [(r.get(0).toString(), r.getLong(1)) for r in expected],
+            )
+        finally:
+            df.unpersist()
+
+    def test_mixed_worker_and_inprocess_udfs(self):
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.functions import udf
+        from pyspark.sql.types import LongType
+
+        double = inprocess_udf(LongType())(lambda x: pc.multiply(x, 2))
+        plus_one = udf(lambda x: x + 1, LongType(), useArrow=False)
+        df = self.spark.range(4)
+        rows = df.select(double(plus_one("id")), 
plus_one(double("id"))).collect()
+        self.assertEqual([tuple(r) for r in rows], [(2 * (i + 1), 2 * i + 1) 
for i in range(4)])
+
+    def test_pipelined_arrow_worker_consumes_inprocess_results(self):
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.functions import arrow_udf
+
+        conf = 
self.spark.sparkContext._jvm.org.apache.spark.SparkEnv.get().conf()
+        key = "spark.python.udf.pipelined.enabled"
+        previous = conf.get(key, "false")
+        conf.set(key, "true")
+        try:
+            double = inprocess_udf("long")(lambda x: pc.multiply(x, 2))
+            triple = inprocess_udf("long")(lambda x: pc.multiply(x, 3))
+            add = arrow_udf(lambda x, y: pc.add(x, y), "long")
+            with 
self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": "2"}):
+                query = self.spark.range(8, 
numPartitions=2).select(add(double("id"), triple("id")))
+                plan = query._jdf.queryExecution().executedPlan().toString()
+                self.assertIn("InProcessArrowEvalPython", plan)
+                self.assertIn("ArrowEvalPython", plan)
+                self.assertEqual([r[0] for r in query.collect()], [i * 5 for i 
in range(8)])
+        finally:
+            conf.set(key, previous)
+
+    def 
test_pipelined_worker_reads_materialized_nested_results_across_batches(self):
+        import pyarrow as pa
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.functions import arrow_udf
+
+        conf = 
self.spark.sparkContext._jvm.org.apache.spark.SparkEnv.get().conf()
+        key = "spark.python.udf.pipelined.enabled"
+        previous = conf.get(key, "false")
+        conf.set(key, "true")
+        try:
+            # The worker's writer thread consumes these rows; each must 
outlive its batch.
+            pair = inprocess_udf("array<string>")(
+                lambda s: pa.array([[v, v] for v in s.to_pylist()], 
pa.list_(pa.string()))
+            )
+            joined = arrow_udf(lambda a: pc.binary_join(a, "-"), "string")
+            with 
self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": "3"}):
+                df = self.spark.range(10, numPartitions=2).selectExpr("CAST(id 
AS STRING) AS s")
+                rows = df.select(joined(pair("s"))).collect()
+                self.assertEqual([r[0] for r in rows], [f"{i}-{i}" for i in 
range(10)])
+                # A pass-through column makes the in-process node buffer and 
join input rows.
+                df = df.selectExpr("s", "CAST(s AS INT) AS id")
+                rows = df.select("id", joined(pair("s"))).collect()
+                self.assertEqual([tuple(r) for r in rows], [(i, f"{i}-{i}") 
for i in range(10)])
+        finally:
+            conf.set(key, previous)
+
+    def 
test_pipelined_worker_stopping_early_does_not_break_inprocess_input(self):
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess import inprocess_udf
+        from pyspark.sql.functions import arrow_udf
+
+        conf = 
self.spark.sparkContext._jvm.org.apache.spark.SparkEnv.get().conf()
+        key = "spark.python.udf.pipelined.enabled"
+        previous = conf.get(key, "false")
+        conf.set(key, "true")
+        try:
+            double = inprocess_udf("long")(lambda x: pc.multiply(x, 2))
+            plus_one = arrow_udf(lambda x: pc.add(x, 1), "long")
+            with 
self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": "100"}):
+                # The task completes after a few rows while the writer thread 
still pulls input.
+                # A filter on the UDF result keeps the limit from being pushed 
below the UDFs.
+                df = self.spark.range(0, 100000, 1, 2).selectExpr("id", "id % 
7 AS k")
+                # A coalesced parent evaluates the in-process node on the 
writer thread.
+                coalesced = df.select(double("id").alias("a"), "k").coalesce(1)
+                queries = [
+                    df.select("k", 
plus_one(double("id")).alias("v")).filter("v > 0").limit(1),
+                    coalesced.select(plus_one("a").alias("v"), "k").filter("v 
> 0").limit(10),
+                ]
+                for query in queries:
+                    plan = 
query._jdf.queryExecution().executedPlan().toString()
+                    self.assertNotIn("Limit", 
plan[plan.index("ArrowEvalPython") :])
+                for _ in range(5):
+                    self.assertEqual(len(queries[0].collect()), 1)
+                    self.assertEqual(len(queries[1].collect()), 10)
+                # Later tasks in the same executor still run correctly.
+                total = 
df.select(plus_one(double("id")).alias("v")).groupBy().sum("v")
+                self.assertEqual(total.first()[0], sum(2 * i + 1 for i in 
range(100000)))
+        finally:
+            conf.set(key, previous)
+
+    def test_computed_and_reordered_arguments_with_pass_through_columns(self):
+        import pyarrow.compute as pc
+
+        from pyspark.inprocess import inprocess_udf
+
+        concat = inprocess_udf("string")(lambda a, b: 
pc.binary_join_element_wise(a, b, ":"))
+        with self.sql_conf({"spark.sql.execution.arrow.maxRecordsPerBatch": 
"3"}):
+            df = self.spark.range(10, numPartitions=2).selectExpr(
+                "id", "CAST(id AS STRING) AS s", "repeat('x', CAST(id AS INT)) 
AS pad"
+            )
+            # Computed and reordered arguments, while id and pad pass through 
unchanged.
+            rows = df.select("id", "pad", concat(df.pad, df.s.substr(1, 
1))).collect()
+        self.assertEqual(
+            [tuple(r) for r in rows], [(i, "x" * i, "x" * i + ":" + str(i)[0]) 
for i in range(10)]
+        )
+
+    def test_input_columns_read_back_from_arrow_are_unchanged(self):
+        import pyarrow as pa
+
+        from pyspark.inprocess import inprocess_udf
+
+        # Every input column is an argument, so the output's input columns 
come from Arrow.

Review Comment:
   Thanks for catching this. Fixed in 8aead4b: `d`, `arr` and `m` moved to the 
Buffered test below, next to the interval, and the ReadBack test now asserts 
through `InProcessArrowEvalPythonEvaluatorFactory.readsBack` that each of its 
column types reads back, so it cannot silently fall back to Buffered again.



##########
python/pyspark/sql/tests/test_inprocess_runtime.py:
##########
@@ -0,0 +1,851 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+
+"""Arrow CDI contract tests that do not need a Spark JVM or JEP."""
+
+import sys
+import threading
+import unittest
+import weakref
+from importlib.util import find_spec
+from unittest.mock import MagicMock, patch
+
+from pyspark import cloudpickle
+from pyspark.sql.types import (
+    ArrayType,
+    BooleanType,
+    DecimalType,
+    FloatType,
+    IntegerType,
+    LongType,
+    StringType,
+    StructField,
+    StructType,
+    TimestampType,
+)
+from pyspark.testing.utils import have_pyarrow
+
+_have_arrow_cdi = have_pyarrow and find_spec("cffi") is not None

Review Comment:
   Done in 8aead4b: the runtime suite is split into `InProcessRuntimeTests`, 
which needs only PyArrow (28 tests), and `InProcessRuntimeCDITests`, which also 
needs cffi (22 tests, the ones that register or invoke through the C Data 
Interface). Without cffi, the first class runs and the second is skipped.



##########
sql/core/src/main/scala/org/apache/spark/sql/execution/python/InProcessArrowEvalPythonEvaluatorFactory.scala:
##########
@@ -0,0 +1,581 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.python
+
+import java.io.File
+import java.nio.file.Files
+import java.util.UUID
+import java.util.concurrent.TimeUnit
+import java.util.concurrent.atomic.{AtomicBoolean, AtomicInteger}
+import java.util.concurrent.locks.ReentrantLock
+
+import scala.collection.mutable.ArrayBuffer
+import scala.jdk.CollectionConverters._
+
+import com.google.common.util.concurrent.Uninterruptibles
+import org.apache.arrow.c.{ArrowArray, ArrowSchema, BaseStruct}
+import org.apache.arrow.util.AutoCloseables
+import org.apache.arrow.vector.VectorSchemaRoot
+
+import org.apache.spark.{SparkEnv, SparkException, TaskContext}
+import org.apache.spark.api.python.ChainedPythonFunctions
+import org.apache.spark.memory.MemoryConsumer
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.{Attribute, Expression, 
JoinedRow, PythonUDF, UnsafeProjection, UnsafeRow}
+import org.apache.spark.sql.execution.arrow.ArrowWriter
+import org.apache.spark.sql.execution.metric.SQLMetric
+import org.apache.spark.sql.execution.python.EvalPythonExec.ArgumentMetadata
+import org.apache.spark.sql.types._
+import org.apache.spark.sql.util.ArrowUtils
+import org.apache.spark.sql.vectorized.{ArrowColumnVector, ColumnarBatch, 
ColumnVector}
+import org.apache.spark.util.Utils
+
+/**
+ * Evaluates scalar Python UDFs using Arrow CDI in the executor process. Only 
UDF arguments
+ * are converted to Arrow. Original rows are buffered in a spillable queue and 
joined with
+ * the results, unless all of them are UDF arguments that read back from Arrow 
unchanged.
+ * Each batch owns its Arrow buffers so Python can safely retain input arrays.
+ *
+ * The evaluator owns its queue, so that cleanup at task completion is 
coordinated with a
+ * consumer on another thread, such as a pipelined Python writer or a 
TRANSFORM feed thread.
+ */
+class InProcessArrowEvalPythonEvaluatorFactory(
+    childOutput: Seq[Attribute],
+    udfs: Seq[PythonUDF],
+    output: Seq[Attribute],
+    batchSize: Int,
+    maxBytes: Long,
+    timeZoneId: String,
+    largeVarTypes: Boolean,
+    hideTraceback: Boolean,
+    simplifiedTraceback: Boolean,
+    tracebackWithLocals: Boolean,
+    fullValidation: Boolean,
+    metrics: Map[String, SQLMetric])
+  extends EvalPythonEvaluatorFactory(childOutput, udfs, output) {
+
+  private[python] def runtimeSession: 
InProcessPythonRuntime.InterpreterSession =
+    InProcessPythonRuntime.currentSession
+
+  /** Unused: `evaluateJoined` always evaluates the UDFs. */
+  override protected def evaluate(
+      funcs: Seq[(ChainedPythonFunctions, Long)],
+      argMetas: Array[Array[ArgumentMetadata]],
+      rows: Iterator[InternalRow],
+      inputSchema: StructType,
+      context: TaskContext): Iterator[InternalRow] =
+    throw SparkException.internalError("In-process UDFs are evaluated with 
their input rows")
+
+  override protected def evaluateJoined(
+      funcs: Seq[(ChainedPythonFunctions, Long)],
+      argMetas: Array[Array[ArgumentMetadata]],
+      rows: Iterator[InternalRow],
+      inputs: Seq[Expression],
+      inputSchema: StructType,
+      context: TaskContext): Option[Iterator[InternalRow]] = {
+    import InProcessArrowEvalPythonEvaluatorFactory.{Buffered, ReadBack, 
readsBack}
+    val inputColumns = inputs.length == childOutput.length && 
inputs.zip(childOutput).forall {
+      case (a: Attribute, c) => a.exprId == c.exprId
+      case _ => false
+    }
+    // If all input columns are UDF arguments, they are written to Arrow 
regardless. Read them
+    // back from the exported input vectors instead of buffering every input 
row, if their
+    // values read back from Arrow exactly as written and as fast as an unsafe 
row copy.
+    val joinInput = if (inputColumns && inputSchema.forall(f => 
readsBack(f.dataType))) {
+      ReadBack
+    } else if (inputColumns) {
+      Buffered(None)
+    } else {
+      // Each projected row is written to Arrow before the next input row is 
pulled, so the
+      // arguments go into a reused buffer rather than being copied value by 
value.
+      val projection = UnsafeProjection.create(inputs, childOutput)
+      projection.initialize(context.partitionId())
+      Buffered(Some(projection))
+    }
+    Some(evaluateBatches(funcs, argMetas, rows, inputSchema, context, 
joinInput))
+  }
+
+  private[python] def evaluateBatches(
+      funcs: Seq[(ChainedPythonFunctions, Long)],
+      argMetas: Array[Array[ArgumentMetadata]],
+      rows: Iterator[InternalRow],
+      inputSchema: StructType,
+      context: TaskContext,
+      joinInput: InProcessArrowEvalPythonEvaluatorFactory.JoinInput): 
Iterator[InternalRow] = {
+    import InProcessArrowEvalPythonEvaluatorFactory.{Buffered, ReadBack}
+    ArrowUtils.failDuplicatedFieldNames(inputSchema)
+    val functions = funcs.map { case (chain, _) =>
+      if (chain.funcs.size != 1) {
+        throw SparkException.internalError(
+          "In-process UDF chains must use separate evaluation nodes")
+      }
+      chain.funcs.head
+    }
+    val inputOrdinals = argMetas.map(_.map(_.offset))
+    def checkCancellation(): Unit = context.killTaskIfInterrupted()
+
+    val expectedFields = udfs.map { udf =>
+      ArrowUtils.toArrowField("result", udf.dataType, true, timeZoneId, 
largeVarTypes)
+    }
+    val processingTime = new 
InProcessArrowEvalPythonEvaluatorFactory.NanosecondTimer(
+      metrics("pythonProcessingTime"))
+    val initTime = new 
InProcessArrowEvalPythonEvaluatorFactory.NanosecondTimer(

Review Comment:
   Done in 8aead4b: `pythonInitTime`, `pythonTotalTime` and 
`pythonProcessingTime` are created with `SQLMetrics.createNanoTimingMetric` 
through `additionalMetrics`, with an empty `timingMetricsDesc`, so they are 
summed in nanoseconds across tasks, and `NanosecondTimer` is gone. The planning 
test checks their metric type.



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