viirya commented on code in PR #6130:
URL: https://github.com/apache/datafusion-comet/pull/6130#discussion_r4227464515


##########
spark/src/main/spark-4.1+/org/apache/spark/sql/comet/CometArrowEvalPythonExec.scala:
##########
@@ -0,0 +1,215 @@
+/*
+ * 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.comet
+
+import java.nio.charset.StandardCharsets
+
+import scala.jdk.CollectionConverters._
+
+import org.apache.spark.api.python.PythonEvalType
+import org.apache.spark.sql.SparkSession
+import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeSet, 
Expression, NamedArgumentExpression, NamedExpression, PythonUDF}
+import org.apache.spark.sql.execution.{PartitioningPreservingUnaryExecNode, 
SparkPlan}
+import org.apache.spark.sql.execution.python.ArrowEvalPythonExec
+import org.apache.spark.sql.types.{BinaryType, BooleanType, ByteType, 
DataType, DateType, DecimalType, DoubleType, FloatType, IntegerType, LongType, 
ShortType, StringType, TimestampNTZType}
+
+import com.google.common.base.Objects
+import com.google.protobuf.ByteString
+
+import org.apache.comet.{CometConf, ConfigEntry, NativeBase}
+import org.apache.comet.CometSparkSessionExtensions.withFallbackReason
+import org.apache.comet.serde.{CometOperatorSerde, Compatible, 
OperatorOuterClass, QueryPlanSerde, SupportLevel, Unsupported}
+import org.apache.comet.serde.OperatorOuterClass.Operator
+
+/** Native execution for Spark 4.1+ scalar `@arrow_udf` functions. */
+object CometArrowEvalPythonExec extends 
CometOperatorSerde[ArrowEvalPythonExec] {
+
+  // SparkContext adds this entry even when the user has not configured a 
Python
+  // environment. Keep other overrides on Spark's worker path.
+  private def hasUnsupportedEnvironment(env: java.util.Map[String, String]): 
Boolean =
+    env != null && env.asScala.exists { case (key, value) =>
+      key != "PYTHONHASHSEED" || value != "0"
+    }
+
+  // PySpark's Accumulator.__reduce__ serializes a reference to
+  // pyspark.accumulators._deserialize_accumulator. Spark's worker forwards its
+  // task-local updates to the JVM when the task finishes; embedded Python does
+  // not have that worker protocol. A match may also come from a harmless 
string
+  // in the pickle, in which case Spark's worker path is the safe choice.
+  private def hasSerializedAccumulator(command: Seq[Byte]): Boolean =
+    new String(command.toArray, 
StandardCharsets.ISO_8859_1).contains("pyspark.accumulators")
+
+  private def hasCompatibleArrowSchema(dataType: DataType): Boolean = dataType 
match {
+    case _: BooleanType | _: ByteType | _: ShortType | _: IntegerType | _: 
LongType |
+        _: FloatType | _: DoubleType | _: BinaryType | _: DateType | _: 
DecimalType |
+        _: TimestampNTZType =>
+      true
+    // Spark's Arrow conversion accepts plain strings. Collated and 
constrained strings
+    // may carry semantics that are not represented by Comet's Utf8 Arrow type.
+    case s: StringType if s == StringType => true
+    case _ => false
+  }
+
+  override def enabledConfig: Option[ConfigEntry[Boolean]] =
+    Some(CometConf.COMET_NATIVE_ARROW_PYTHON_UDF_ENABLED)
+
+  override def getSupportLevel(op: ArrowEvalPythonExec): SupportLevel = {
+    if (!NativeBase.supportsPythonUdf()) {
+      return Unsupported(Some("Native library lacks the python-udf feature"))
+    }
+    if (op.evalType != PythonEvalType.SQL_SCALAR_ARROW_UDF) {
+      return Unsupported(Some("Only scalar @arrow_udf is supported"))
+    }
+    if (op.udfs.isEmpty || op.udfs.length != op.resultAttrs.length) {
+      return Unsupported(Some("Arrow UDF functions and result attributes do 
not match"))
+    }
+    if (op.conf.arrowUseLargeVarTypes) {
+      return Unsupported(Some("Arrow UDF large variable types are not 
supported in-process"))
+    }
+    if (op.conf.pythonUDFProfiler.nonEmpty) {
+      return Unsupported(Some("Arrow UDF profiling is not supported 
in-process"))
+    }
+    if (SparkSession.active.sparkContext.listFiles().nonEmpty) {

Review Comment:
   Fixed in `794b2767f`: the support check now also falls back when 
`SparkContext.listArchives()` is non-empty. `test_native_arrow_udf_files.py` 
has a new `addArchive` case that reads `offset.txt` from an extracted ZIP 
through `SparkFiles.get()` and asserts that the plan stays on 
`ArrowEvalPythonExec` with results `[7, 8]`.



##########
native/core/src/execution/python_udf.rs:
##########
@@ -0,0 +1,453 @@
+// 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.
+
+//! In-process bridge for Spark 4.1+ scalar Arrow UDFs. Each instance owns one
+//! unpickled Python callable and must be created for one Spark task/partition.
+//! The public API deliberately deals in Arrow arrays; the physical operator is
+//! responsible for evaluating Catalyst arguments and preserving input columns.
+
+use arrow::array::{make_array, Array, ArrayRef};
+use arrow::datatypes::DataType;
+use arrow::error::{ArrowError, Result};
+use arrow::ffi::{from_ffi, FFI_ArrowArray, FFI_ArrowSchema};
+use pyo3::ffi::Py_uintptr_t;
+use pyo3::prelude::*;
+use pyo3::types::{PyBytes, PyTuple};
+
+fn initialize_python() -> Result<()> {
+    use std::ffi::CStr;
+    use std::sync::OnceLock;
+
+    static RESULT: OnceLock<std::result::Result<(), String>> = OnceLock::new();
+    RESULT
+        .get_or_init(|| {
+            // Spark sets PYTHONHASHSEED=0 on its Python workers by default.
+            // Match that seed before any Python object is created in the 
embedded
+            // interpreter, without changing the JVM process environment.
+            // SAFETY: OnceLock serializes initialization by Comet. No other 
Comet
+            // code accesses the Python C API before this function returns.
+            unsafe {
+                if pyo3::ffi::Py_IsInitialized() != 0 {
+                    return Ok(());
+                }
+                let mut config = 
std::mem::MaybeUninit::<pyo3::ffi::PyConfig>::uninit();
+                pyo3::ffi::PyConfig_InitPythonConfig(config.as_mut_ptr());
+                let mut config = config.assume_init();
+                config.install_signal_handlers = 0;
+                config.use_hash_seed = 1;
+                config.hash_seed = 0;
+                let status = pyo3::ffi::Py_InitializeFromConfig(&config);
+                let error = if pyo3::ffi::PyStatus_Exception(status) != 0 {
+                    if status.err_msg.is_null() {
+                        "Python interpreter initialization failed".to_string()
+                    } else {
+                        CStr::from_ptr(status.err_msg)
+                            .to_string_lossy()
+                            .into_owned()
+                    }
+                } else {
+                    String::new()
+                };
+                pyo3::ffi::PyConfig_Clear(&mut config);
+                if !error.is_empty() {
+                    return Err(error);
+                }
+                pyo3::ffi::PyEval_SaveThread();
+                Ok(())
+            }
+        })
+        .clone()
+        .map_err(ArrowError::ComputeError)
+}
+
+#[cfg(target_os = "linux")]
+fn make_python_symbols_global() -> Result<()> {
+    use std::ffi::CStr;
+    use std::sync::OnceLock;
+
+    static RESULT: OnceLock<std::result::Result<(), String>> = OnceLock::new();
+    RESULT
+        .get_or_init(|| {
+            // The JVM loads libcomet with RTLD_LOCAL. Its libpython 
dependency is
+            // local too, but CPython extension modules resolve Python C API
+            // symbols from the global namespace when they are imported.
+            let mut info = std::mem::MaybeUninit::<libc::Dl_info>::uninit();
+            // SAFETY: Py_Initialize is a linked function address and info is
+            // writable storage for dladdr's result.
+            if unsafe {
+                libc::dladdr(
+                    pyo3::ffi::Py_Initialize as *const () as *const 
libc::c_void,
+                    info.as_mut_ptr(),
+                )
+            } == 0
+            {
+                return Err("cannot locate the linked Python 
library".to_string());
+            }
+            // SAFETY: dladdr initialized info on success and dli_fname is a
+            // null-terminated path valid for the duration of this call.
+            let info = unsafe { info.assume_init() };
+            if info.dli_fname.is_null() {
+                return Err("linked Python library has no path".to_string());
+            }
+            let path = unsafe { CStr::from_ptr(info.dli_fname) };
+            // RTLD_NOLOAD promotes the already-loaded libpython rather than
+            // loading a second copy with separate interpreter state. Keep the
+            // handle for the executor lifetime so its symbols remain global.
+            // SAFETY: path points to a valid C string returned by dladdr.
+            if unsafe {
+                libc::dlopen(
+                    path.as_ptr(),
+                    libc::RTLD_NOW | libc::RTLD_GLOBAL | libc::RTLD_NOLOAD,
+                )
+            }
+            .is_null()
+            {
+                // SAFETY: dlerror returns a null-terminated message, if any.
+                let error = unsafe { libc::dlerror() };
+                let detail = if error.is_null() {
+                    "unknown dynamic loader error".to_string()
+                } else {
+                    unsafe { CStr::from_ptr(error) }
+                        .to_string_lossy()
+                        .into_owned()
+                };
+                return Err(format!("cannot expose Python C API symbols: 
{detail}"));
+            }
+            Ok(())
+        })
+        .clone()
+        .map_err(ArrowError::ComputeError)
+}
+
+#[cfg(not(target_os = "linux"))]
+fn make_python_symbols_global() -> Result<()> {
+    Ok(())
+}
+
+/// A scalar Arrow UDF loaded from Spark's pickled `(function, returnType)` 
command.
+/// Spark serializes the return type for its worker; Comet uses the separately
+/// serialized Arrow type from the physical plan instead.
+pub struct ArrowPythonUdf {
+    callable: Py<PyAny>,
+    return_type: DataType,
+    allow_cast: bool,
+    safe_cast: bool,
+}
+
+impl ArrowPythonUdf {
+    pub fn from_command(
+        command: &[u8],
+        return_type: DataType,
+        allow_cast: bool,
+        safe_cast: bool,
+        python_version: &str,
+    ) -> Result<Self> {
+        make_python_symbols_global()?;
+        initialize_python()?;
+        Python::attach(|py| {
+            if !python_version.is_empty() {
+                let info = py
+                    .import("sys")
+                    .map_err(python_error)?
+                    .getattr("version_info")
+                    .map_err(python_error)?;
+                let major: u8 = info
+                    .get_item(0)
+                    .map_err(python_error)?
+                    .extract()
+                    .map_err(python_error)?;
+                let minor: u8 = info
+                    .get_item(1)
+                    .map_err(python_error)?
+                    .extract()
+                    .map_err(python_error)?;
+                let actual = format!("{major}.{minor}");
+                if actual != python_version {
+                    return Err(ArrowError::ComputeError(format!(
+                        "Arrow UDF requires Python {python_version}, embedded 
interpreter is {actual}"
+                    )));
+                }
+            }
+            let pickle = py.import("pickle").map_err(python_error)?;
+            let loaded = pickle
+                .call_method1("loads", (PyBytes::new(py, command),))
+                .map_err(python_error)?;
+            let tuple = loaded.cast::<PyTuple>().map_err(python_error)?;
+            if tuple.len() != 2 {
+                return Err(ArrowError::ComputeError(format!(
+                    "Arrow UDF command must contain (function, returnType), 
got {} items",
+                    tuple.len()
+                )));
+            }
+            let callable = tuple.get_item(0).map_err(python_error)?;
+            if !callable.is_callable() {
+                return Err(ArrowError::ComputeError(
+                    "Arrow UDF command does not contain a 
callable".to_string(),
+                ));
+            }
+            Ok(Self {
+                callable: callable.unbind(),
+                return_type,
+                allow_cast,
+                safe_cast,
+            })
+        })
+    }
+
+    /// Evaluate one Arrow batch, with the same row count for every argument.
+    /// Python receives and returns `pyarrow.Array` objects via the Arrow C 
Data
+    /// interface; no row conversion or Arrow IPC serialization occurs here.
+    pub fn evaluate(&self, args: &[ArrayRef], num_rows: usize) -> 
Result<ArrayRef> {
+        let names = vec![String::new(); args.len()];
+        self.evaluate_named(args, &names, num_rows)
+    }
+
+    pub fn evaluate_named(
+        &self,
+        args: &[ArrayRef],
+        names: &[String],
+        num_rows: usize,
+    ) -> Result<ArrayRef> {
+        if args.len() != names.len() {
+            return Err(ArrowError::ComputeError(
+                "Arrow UDF argument names are not aligned with 
arguments".to_string(),
+            ));
+        }
+        for (index, arg) in args.iter().enumerate() {
+            if arg.len() != num_rows {
+                return Err(ArrowError::ComputeError(format!(
+                    "Arrow UDF argument {index} has {} rows, expected 
{num_rows}",
+                    arg.len()
+                )));
+            }
+        }
+
+        Python::attach(|py| {
+            let pa = py.import("pyarrow").map_err(python_error)?;
+            let array_class = pa.getattr("Array").map_err(python_error)?;
+            let mut py_args = Vec::with_capacity(args.len());
+            for arg in args {
+                let data = arg.to_data();
+                // PyArrow takes ownership of these C Data structs and clears 
their
+                // release callbacks, so the pointed-to storage must be 
writable.
+                let mut ffi_array = FFI_ArrowArray::new(&data);
+                let mut ffi_schema = 
FFI_ArrowSchema::try_from(data.data_type())?;
+                let py_arg = array_class
+                    .call_method1(
+                        "_import_from_c",
+                        (
+                            &raw mut ffi_array as Py_uintptr_t,
+                            &raw mut ffi_schema as Py_uintptr_t,
+                        ),
+                    )
+                    .map_err(python_error)?;
+                py_args.push(py_arg);
+            }
+
+            let kwargs = pyo3::types::PyDict::new(py);
+            let mut positional = Vec::new();
+            for (arg, name) in py_args.into_iter().zip(names) {
+                if name.is_empty() {
+                    positional.push(arg);
+                } else {
+                    kwargs.set_item(name, arg).map_err(python_error)?;
+                }
+            }
+            let result = self
+                .callable
+                .bind(py)
+                .call(
+                    PyTuple::new(py, positional).map_err(python_error)?,
+                    Some(&kwargs),
+                )
+                .map_err(python_error)?;
+            if !result.is_instance(&array_class).map_err(python_error)? {
+                return Err(ArrowError::ComputeError(
+                    "Arrow UDF must return a pyarrow.Array".to_string(),
+                ));
+            }
+            let result_len = result.len().map_err(python_error)?;
+            if result_len != num_rows {
+                return Err(ArrowError::ComputeError(format!(
+                    "Arrow UDF returned {result_len} rows, expected {num_rows}"
+                )));
+            }
+
+            let mut ffi_return_type = 
FFI_ArrowSchema::try_from(&self.return_type)?;
+            let expected_type = pa
+                .getattr("DataType")
+                .map_err(python_error)?
+                .call_method1(
+                    "_import_from_c",
+                    (&raw mut ffi_return_type as Py_uintptr_t,),
+                )
+                .map_err(python_error)?;
+            let actual_type = result.getattr("type").map_err(python_error)?;
+            let typed_result = if 
actual_type.eq(&expected_type).map_err(python_error)? {
+                result
+            } else if self.allow_cast {
+                let kwargs = pyo3::types::PyDict::new(py);
+                kwargs
+                    .set_item("safe", self.safe_cast)
+                    .map_err(python_error)?;
+                result
+                    .call_method("cast", (expected_type,), Some(&kwargs))
+                    .map_err(python_error)?
+            } else {
+                return Err(ArrowError::ComputeError(format!(
+                    "Arrow UDF returned type {}, expected {}",
+                    actual_type.str().map_err(python_error)?,
+                    expected_type.str().map_err(python_error)?
+                )));
+            };
+
+            let mut out_array = FFI_ArrowArray::empty();
+            let mut out_schema = FFI_ArrowSchema::empty();
+            typed_result
+                .call_method1(
+                    "_export_to_c",
+                    (
+                        &raw mut out_array as Py_uintptr_t,
+                        &raw mut out_schema as Py_uintptr_t,
+                    ),
+                )
+                .map_err(python_error)?;
+            // SAFETY: PyArrow filled both C Data structs and transferred 
ownership

Review Comment:
   Fixed in `794b2767f`. The result now goes through `decode_string_arrays`, as 
the JVM UDF bridge does, and the SAFETY comment now says that `from_ffi` checks 
the schema but does not validate buffers. A Rust test returns `pa.array([b'ok', 
b'\xff'], pa.binary()).cast(pa.string(), safe=False)` and checks that the 
imported array is valid UTF-8. A Scala test feeds the same unsafe cast into a 
native `length` and compares the result with Spark.



##########
native/core/src/execution/python_udf.rs:
##########
@@ -0,0 +1,453 @@
+// 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.
+
+//! In-process bridge for Spark 4.1+ scalar Arrow UDFs. Each instance owns one
+//! unpickled Python callable and must be created for one Spark task/partition.
+//! The public API deliberately deals in Arrow arrays; the physical operator is
+//! responsible for evaluating Catalyst arguments and preserving input columns.
+
+use arrow::array::{make_array, Array, ArrayRef};
+use arrow::datatypes::DataType;
+use arrow::error::{ArrowError, Result};
+use arrow::ffi::{from_ffi, FFI_ArrowArray, FFI_ArrowSchema};
+use pyo3::ffi::Py_uintptr_t;
+use pyo3::prelude::*;
+use pyo3::types::{PyBytes, PyTuple};
+
+fn initialize_python() -> Result<()> {
+    use std::ffi::CStr;
+    use std::sync::OnceLock;
+
+    static RESULT: OnceLock<std::result::Result<(), String>> = OnceLock::new();
+    RESULT
+        .get_or_init(|| {
+            // Spark sets PYTHONHASHSEED=0 on its Python workers by default.
+            // Match that seed before any Python object is created in the 
embedded
+            // interpreter, without changing the JVM process environment.
+            // SAFETY: OnceLock serializes initialization by Comet. No other 
Comet
+            // code accesses the Python C API before this function returns.
+            unsafe {
+                if pyo3::ffi::Py_IsInitialized() != 0 {
+                    return Ok(());
+                }
+                let mut config = 
std::mem::MaybeUninit::<pyo3::ffi::PyConfig>::uninit();
+                pyo3::ffi::PyConfig_InitPythonConfig(config.as_mut_ptr());
+                let mut config = config.assume_init();
+                config.install_signal_handlers = 0;
+                config.use_hash_seed = 1;
+                config.hash_seed = 0;
+                let status = pyo3::ffi::Py_InitializeFromConfig(&config);
+                let error = if pyo3::ffi::PyStatus_Exception(status) != 0 {
+                    if status.err_msg.is_null() {
+                        "Python interpreter initialization failed".to_string()
+                    } else {
+                        CStr::from_ptr(status.err_msg)
+                            .to_string_lossy()
+                            .into_owned()
+                    }
+                } else {
+                    String::new()
+                };
+                pyo3::ffi::PyConfig_Clear(&mut config);
+                if !error.is_empty() {
+                    return Err(error);
+                }
+                pyo3::ffi::PyEval_SaveThread();
+                Ok(())
+            }
+        })
+        .clone()
+        .map_err(ArrowError::ComputeError)
+}
+
+#[cfg(target_os = "linux")]
+fn make_python_symbols_global() -> Result<()> {
+    use std::ffi::CStr;
+    use std::sync::OnceLock;
+
+    static RESULT: OnceLock<std::result::Result<(), String>> = OnceLock::new();
+    RESULT
+        .get_or_init(|| {
+            // The JVM loads libcomet with RTLD_LOCAL. Its libpython 
dependency is
+            // local too, but CPython extension modules resolve Python C API
+            // symbols from the global namespace when they are imported.
+            let mut info = std::mem::MaybeUninit::<libc::Dl_info>::uninit();
+            // SAFETY: Py_Initialize is a linked function address and info is
+            // writable storage for dladdr's result.
+            if unsafe {
+                libc::dladdr(
+                    pyo3::ffi::Py_Initialize as *const () as *const 
libc::c_void,
+                    info.as_mut_ptr(),
+                )
+            } == 0
+            {
+                return Err("cannot locate the linked Python 
library".to_string());
+            }
+            // SAFETY: dladdr initialized info on success and dli_fname is a
+            // null-terminated path valid for the duration of this call.
+            let info = unsafe { info.assume_init() };
+            if info.dli_fname.is_null() {
+                return Err("linked Python library has no path".to_string());
+            }
+            let path = unsafe { CStr::from_ptr(info.dli_fname) };
+            // RTLD_NOLOAD promotes the already-loaded libpython rather than
+            // loading a second copy with separate interpreter state. Keep the
+            // handle for the executor lifetime so its symbols remain global.
+            // SAFETY: path points to a valid C string returned by dladdr.
+            if unsafe {
+                libc::dlopen(
+                    path.as_ptr(),
+                    libc::RTLD_NOW | libc::RTLD_GLOBAL | libc::RTLD_NOLOAD,
+                )
+            }
+            .is_null()
+            {
+                // SAFETY: dlerror returns a null-terminated message, if any.
+                let error = unsafe { libc::dlerror() };
+                let detail = if error.is_null() {
+                    "unknown dynamic loader error".to_string()
+                } else {
+                    unsafe { CStr::from_ptr(error) }
+                        .to_string_lossy()
+                        .into_owned()
+                };
+                return Err(format!("cannot expose Python C API symbols: 
{detail}"));
+            }
+            Ok(())
+        })
+        .clone()
+        .map_err(ArrowError::ComputeError)
+}
+
+#[cfg(not(target_os = "linux"))]
+fn make_python_symbols_global() -> Result<()> {
+    Ok(())
+}
+
+/// A scalar Arrow UDF loaded from Spark's pickled `(function, returnType)` 
command.
+/// Spark serializes the return type for its worker; Comet uses the separately
+/// serialized Arrow type from the physical plan instead.
+pub struct ArrowPythonUdf {
+    callable: Py<PyAny>,
+    return_type: DataType,
+    allow_cast: bool,
+    safe_cast: bool,
+}
+
+impl ArrowPythonUdf {
+    pub fn from_command(
+        command: &[u8],
+        return_type: DataType,
+        allow_cast: bool,
+        safe_cast: bool,
+        python_version: &str,
+    ) -> Result<Self> {
+        make_python_symbols_global()?;
+        initialize_python()?;
+        Python::attach(|py| {
+            if !python_version.is_empty() {
+                let info = py
+                    .import("sys")
+                    .map_err(python_error)?
+                    .getattr("version_info")
+                    .map_err(python_error)?;
+                let major: u8 = info
+                    .get_item(0)
+                    .map_err(python_error)?
+                    .extract()
+                    .map_err(python_error)?;
+                let minor: u8 = info
+                    .get_item(1)
+                    .map_err(python_error)?
+                    .extract()
+                    .map_err(python_error)?;
+                let actual = format!("{major}.{minor}");
+                if actual != python_version {
+                    return Err(ArrowError::ComputeError(format!(
+                        "Arrow UDF requires Python {python_version}, embedded 
interpreter is {actual}"
+                    )));
+                }
+            }
+            let pickle = py.import("pickle").map_err(python_error)?;
+            let loaded = pickle
+                .call_method1("loads", (PyBytes::new(py, command),))
+                .map_err(python_error)?;
+            let tuple = loaded.cast::<PyTuple>().map_err(python_error)?;
+            if tuple.len() != 2 {
+                return Err(ArrowError::ComputeError(format!(
+                    "Arrow UDF command must contain (function, returnType), 
got {} items",
+                    tuple.len()
+                )));
+            }
+            let callable = tuple.get_item(0).map_err(python_error)?;
+            if !callable.is_callable() {
+                return Err(ArrowError::ComputeError(
+                    "Arrow UDF command does not contain a 
callable".to_string(),
+                ));
+            }
+            Ok(Self {
+                callable: callable.unbind(),
+                return_type,
+                allow_cast,
+                safe_cast,
+            })
+        })
+    }
+
+    /// Evaluate one Arrow batch, with the same row count for every argument.
+    /// Python receives and returns `pyarrow.Array` objects via the Arrow C 
Data
+    /// interface; no row conversion or Arrow IPC serialization occurs here.
+    pub fn evaluate(&self, args: &[ArrayRef], num_rows: usize) -> 
Result<ArrayRef> {
+        let names = vec![String::new(); args.len()];
+        self.evaluate_named(args, &names, num_rows)
+    }
+
+    pub fn evaluate_named(
+        &self,
+        args: &[ArrayRef],
+        names: &[String],
+        num_rows: usize,
+    ) -> Result<ArrayRef> {
+        if args.len() != names.len() {
+            return Err(ArrowError::ComputeError(
+                "Arrow UDF argument names are not aligned with 
arguments".to_string(),
+            ));
+        }
+        for (index, arg) in args.iter().enumerate() {
+            if arg.len() != num_rows {
+                return Err(ArrowError::ComputeError(format!(
+                    "Arrow UDF argument {index} has {} rows, expected 
{num_rows}",
+                    arg.len()
+                )));
+            }
+        }
+
+        Python::attach(|py| {
+            let pa = py.import("pyarrow").map_err(python_error)?;
+            let array_class = pa.getattr("Array").map_err(python_error)?;
+            let mut py_args = Vec::with_capacity(args.len());
+            for arg in args {
+                let data = arg.to_data();
+                // PyArrow takes ownership of these C Data structs and clears 
their
+                // release callbacks, so the pointed-to storage must be 
writable.
+                let mut ffi_array = FFI_ArrowArray::new(&data);
+                let mut ffi_schema = 
FFI_ArrowSchema::try_from(data.data_type())?;
+                let py_arg = array_class
+                    .call_method1(
+                        "_import_from_c",
+                        (
+                            &raw mut ffi_array as Py_uintptr_t,
+                            &raw mut ffi_schema as Py_uintptr_t,
+                        ),
+                    )
+                    .map_err(python_error)?;
+                py_args.push(py_arg);
+            }
+
+            let kwargs = pyo3::types::PyDict::new(py);
+            let mut positional = Vec::new();
+            for (arg, name) in py_args.into_iter().zip(names) {
+                if name.is_empty() {
+                    positional.push(arg);
+                } else {
+                    kwargs.set_item(name, arg).map_err(python_error)?;
+                }
+            }
+            let result = self
+                .callable
+                .bind(py)
+                .call(
+                    PyTuple::new(py, positional).map_err(python_error)?,
+                    Some(&kwargs),
+                )
+                .map_err(python_error)?;
+            if !result.is_instance(&array_class).map_err(python_error)? {

Review Comment:
   Fixed in `794b2767f`. On Spark 4.2+ the serde sets a new 
`accept_array_like_results` flag. When it is set, the bridge takes 
`pa.RecordBatch.from_arrays([result], ["_0"]).column(0)` before the length 
check and the cast, so lists and NumPy arrays work and a `ChunkedArray` is 
still rejected. Spark 4.1 still requires a `pa.Array`. A Rust test covers both 
modes and the chunked rejection. A Spark 4.2 test compares `to_pylist()` and 
NumPy results with Spark.



##########
spark/src/main/spark-4.1+/org/apache/spark/sql/comet/CometArrowEvalPythonExec.scala:
##########
@@ -0,0 +1,215 @@
+/*
+ * 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.comet
+
+import java.nio.charset.StandardCharsets
+
+import scala.jdk.CollectionConverters._
+
+import org.apache.spark.api.python.PythonEvalType
+import org.apache.spark.sql.SparkSession
+import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeSet, 
Expression, NamedArgumentExpression, NamedExpression, PythonUDF}
+import org.apache.spark.sql.execution.{PartitioningPreservingUnaryExecNode, 
SparkPlan}
+import org.apache.spark.sql.execution.python.ArrowEvalPythonExec
+import org.apache.spark.sql.types.{BinaryType, BooleanType, ByteType, 
DataType, DateType, DecimalType, DoubleType, FloatType, IntegerType, LongType, 
ShortType, StringType, TimestampNTZType}
+
+import com.google.common.base.Objects
+import com.google.protobuf.ByteString
+
+import org.apache.comet.{CometConf, ConfigEntry, NativeBase}
+import org.apache.comet.CometSparkSessionExtensions.withFallbackReason
+import org.apache.comet.serde.{CometOperatorSerde, Compatible, 
OperatorOuterClass, QueryPlanSerde, SupportLevel, Unsupported}
+import org.apache.comet.serde.OperatorOuterClass.Operator
+
+/** Native execution for Spark 4.1+ scalar `@arrow_udf` functions. */
+object CometArrowEvalPythonExec extends 
CometOperatorSerde[ArrowEvalPythonExec] {
+
+  // SparkContext adds this entry even when the user has not configured a 
Python
+  // environment. Keep other overrides on Spark's worker path.
+  private def hasUnsupportedEnvironment(env: java.util.Map[String, String]): 
Boolean =
+    env != null && env.asScala.exists { case (key, value) =>
+      key != "PYTHONHASHSEED" || value != "0"
+    }
+
+  // PySpark's Accumulator.__reduce__ serializes a reference to
+  // pyspark.accumulators._deserialize_accumulator. Spark's worker forwards its
+  // task-local updates to the JVM when the task finishes; embedded Python does
+  // not have that worker protocol. A match may also come from a harmless 
string
+  // in the pickle, in which case Spark's worker path is the safe choice.
+  private def hasSerializedAccumulator(command: Seq[Byte]): Boolean =
+    new String(command.toArray, 
StandardCharsets.ISO_8859_1).contains("pyspark.accumulators")
+
+  private def hasCompatibleArrowSchema(dataType: DataType): Boolean = dataType 
match {
+    case _: BooleanType | _: ByteType | _: ShortType | _: IntegerType | _: 
LongType |
+        _: FloatType | _: DoubleType | _: BinaryType | _: DateType | _: 
DecimalType |
+        _: TimestampNTZType =>
+      true
+    // Spark's Arrow conversion accepts plain strings. Collated and 
constrained strings
+    // may carry semantics that are not represented by Comet's Utf8 Arrow type.
+    case s: StringType if s == StringType => true
+    case _ => false
+  }
+
+  override def enabledConfig: Option[ConfigEntry[Boolean]] =
+    Some(CometConf.COMET_NATIVE_ARROW_PYTHON_UDF_ENABLED)
+
+  override def getSupportLevel(op: ArrowEvalPythonExec): SupportLevel = {
+    if (!NativeBase.supportsPythonUdf()) {
+      return Unsupported(Some("Native library lacks the python-udf feature"))
+    }
+    if (op.evalType != PythonEvalType.SQL_SCALAR_ARROW_UDF) {
+      return Unsupported(Some("Only scalar @arrow_udf is supported"))
+    }
+    if (op.udfs.isEmpty || op.udfs.length != op.resultAttrs.length) {
+      return Unsupported(Some("Arrow UDF functions and result attributes do 
not match"))
+    }
+    if (op.conf.arrowUseLargeVarTypes) {
+      return Unsupported(Some("Arrow UDF large variable types are not 
supported in-process"))
+    }
+    if (op.conf.pythonUDFProfiler.nonEmpty) {

Review Comment:
   Fixed in `794b2767f`: native planning falls back when 
`op.conf.pythonWorkerLoggingEnabled` is set. The planning test next to the 
profiler check enables `spark.sql.pyspark.worker.logging.enabled` and asserts 
both the fallback and its reason.



##########
spark/src/main/spark-4.1+/org/apache/spark/sql/comet/CometArrowEvalPythonExec.scala:
##########
@@ -0,0 +1,215 @@
+/*
+ * 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.comet
+
+import java.nio.charset.StandardCharsets
+
+import scala.jdk.CollectionConverters._
+
+import org.apache.spark.api.python.PythonEvalType
+import org.apache.spark.sql.SparkSession
+import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeSet, 
Expression, NamedArgumentExpression, NamedExpression, PythonUDF}
+import org.apache.spark.sql.execution.{PartitioningPreservingUnaryExecNode, 
SparkPlan}
+import org.apache.spark.sql.execution.python.ArrowEvalPythonExec
+import org.apache.spark.sql.types.{BinaryType, BooleanType, ByteType, 
DataType, DateType, DecimalType, DoubleType, FloatType, IntegerType, LongType, 
ShortType, StringType, TimestampNTZType}
+
+import com.google.common.base.Objects
+import com.google.protobuf.ByteString
+
+import org.apache.comet.{CometConf, ConfigEntry, NativeBase}
+import org.apache.comet.CometSparkSessionExtensions.withFallbackReason
+import org.apache.comet.serde.{CometOperatorSerde, Compatible, 
OperatorOuterClass, QueryPlanSerde, SupportLevel, Unsupported}
+import org.apache.comet.serde.OperatorOuterClass.Operator
+
+/** Native execution for Spark 4.1+ scalar `@arrow_udf` functions. */
+object CometArrowEvalPythonExec extends 
CometOperatorSerde[ArrowEvalPythonExec] {
+
+  // SparkContext adds this entry even when the user has not configured a 
Python
+  // environment. Keep other overrides on Spark's worker path.
+  private def hasUnsupportedEnvironment(env: java.util.Map[String, String]): 
Boolean =

Review Comment:
   Changed in `794b2767f`: an entry is now accepted when 
`spark.executorEnv.<key>` has the same value, since cluster managers set those 
variables on the executor process that hosts the interpreter. A local-mode 
executor runs in the driver JVM, which Spark does not launch with 
`spark.executorEnv.*`, so in local mode the driver's own environment must also 
have that value; otherwise the query falls back. `PYTHONHASHSEED` still has to 
be `0`, because the embedded interpreter always starts with that seed. The 
setup section now points to `spark.executorEnv.PYTHONPATH` and describes the 
local-mode caveat.



##########
native/core/src/execution/operators/arrow_python_udf.rs:
##########
@@ -0,0 +1,441 @@
+// 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.
+
+use std::fmt::Formatter;
+use std::sync::Arc;
+
+use arrow::array::{ArrayRef, BinaryArray, RecordBatch, StringArray};
+use arrow::datatypes::{DataType, Field, Schema, SchemaRef, TimeUnit};
+use datafusion::common::tree_node::TreeNodeRecursion;
+use datafusion::common::{exec_err, Result};
+use datafusion::execution::TaskContext;
+use datafusion::physical_expr::{EquivalenceProperties, PhysicalExpr};
+use datafusion::physical_plan::execution_plan::EmissionType;
+use datafusion::physical_plan::stream::RecordBatchStreamAdapter;
+use datafusion::physical_plan::{
+    apply_expression_roots, DisplayAs, DisplayFormatType, ExecutionPlan, 
ExecutionPlanProperties,
+    PlanProperties, SendableRecordBatchStream,
+};
+use futures::stream;
+use futures::StreamExt;
+
+use crate::execution::python_udf::ArrowPythonUdf;
+
+#[derive(Debug, Clone)]
+pub struct ArrowPythonUdfSpec {
+    pub command: Vec<u8>,
+    pub args: Vec<Arc<dyn PhysicalExpr>>,
+    pub arg_names: Vec<String>,
+    pub return_type: DataType,
+    pub return_name: String,
+    pub python_version: String,
+}
+
+/// Evaluates scalar PyArrow UDFs inside the native pipeline. Workers are
+/// instantiated in `execute`, once per partition. Python module state remains
+/// shared by every task in the executor's embedded interpreter.
+#[derive(Debug)]
+pub struct ArrowPythonUdfExec {
+    child: Arc<dyn ExecutionPlan>,
+    specs: Vec<ArrowPythonUdfSpec>,
+    max_records_per_batch: usize,
+    max_bytes_per_batch: usize,
+    schema: SchemaRef,
+    cache: Arc<PlanProperties>,
+}
+
+impl ArrowPythonUdfExec {
+    pub fn try_new(
+        child: Arc<dyn ExecutionPlan>,
+        specs: Vec<ArrowPythonUdfSpec>,
+        max_records_per_batch: i32,
+        max_bytes_per_batch: i64,
+    ) -> Result<Self> {
+        if specs.is_empty() {
+            return exec_err!("ArrowPythonUdfExec requires at least one UDF");
+        }
+        let mut fields: Vec<Field> = child
+            .schema()
+            .fields()
+            .iter()
+            .map(|f| f.as_ref().clone())
+            .collect();
+        for spec in &specs {
+            if spec.args.len() != spec.arg_names.len() {
+                return exec_err!("ArrowPythonUdf argument names are not 
aligned with arguments");
+            }
+            for arg in &spec.args {
+                arg.data_type(&child.schema())?;
+            }
+            fields.push(Field::new(
+                &spec.return_name,
+                spec.return_type.clone(),
+                true,
+            ));
+        }
+        let schema = Arc::new(Schema::new(fields));
+        let cache = Arc::new(PlanProperties::new(
+            EquivalenceProperties::new(Arc::clone(&schema)),
+            child.output_partitioning().clone(),
+            EmissionType::Incremental,
+            child.boundedness(),
+        ));
+        Ok(Self {
+            child,
+            specs,
+            max_records_per_batch: max_records_per_batch.max(0) as usize,
+            max_bytes_per_batch: max_bytes_per_batch.max(0) as usize,
+            schema,
+            cache,
+        })
+    }
+
+    fn evaluate_args(
+        specs: &[ArrowPythonUdfSpec],
+        batch: &RecordBatch,
+    ) -> Result<Vec<Vec<ArrayRef>>> {
+        specs
+            .iter()
+            .map(|spec| {
+                spec.args
+                    .iter()
+                    .map(|arg| 
arg.evaluate(batch)?.into_array(batch.num_rows()))
+                    .collect::<Result<Vec<_>>>()
+            })
+            .collect()
+    }
+
+    // Spark's row-based Arrow writer checks its buffer size after each row, so
+    // the row that reaches the byte limit remains in that batch. The native
+    // path uses logical Arrow buffer sizes for its verified scalar types.
+    fn input_bytes(args: &[Vec<ArrayRef>], offset: usize, length: usize) -> 
Result<usize> {
+        if length == 0 {
+            return Ok(0);
+        }
+        let mut bytes = 0usize;
+        for array in args.iter().flatten() {
+            let value_bytes = match array.data_type() {
+                DataType::Boolean => length.div_ceil(8),
+                DataType::Int8 | DataType::UInt8 => length,
+                DataType::Int16 | DataType::UInt16 => length.saturating_mul(2),
+                DataType::Int32 | DataType::UInt32 | DataType::Float32 | 
DataType::Date32 => {
+                    length.saturating_mul(4)
+                }
+                DataType::Int64
+                | DataType::UInt64
+                | DataType::Float64
+                | DataType::Timestamp(TimeUnit::Microsecond, None) => 
length.saturating_mul(8),
+                DataType::Decimal128(_, _) => length.saturating_mul(16),
+                DataType::Utf8 => {
+                    let values = array
+                        .as_any()
+                        .downcast_ref::<StringArray>()
+                        .ok_or_else(|| {
+                            datafusion::error::DataFusionError::Execution(
+                                "Arrow UDF string argument has an unexpected 
array type"
+                                    .to_string(),
+                            )
+                        })?;
+                    let offsets = values.value_offsets();
+                    (offsets[offset + length] - offsets[offset]) as usize
+                        + (length + 1).saturating_mul(4)
+                }
+                DataType::Binary => {
+                    let values = array
+                        .as_any()
+                        .downcast_ref::<BinaryArray>()
+                        .ok_or_else(|| {
+                            datafusion::error::DataFusionError::Execution(
+                                "Arrow UDF binary argument has an unexpected 
array type"
+                                    .to_string(),
+                            )
+                        })?;
+                    let offsets = values.value_offsets();
+                    (offsets[offset + length] - offsets[offset]) as usize
+                        + (length + 1).saturating_mul(4)
+                }
+                other => return exec_err!("Unsupported Arrow UDF argument 
type: {other}"),
+            };
+            bytes = bytes.saturating_add(value_bytes);
+            // Arrow Java's getBufferSizeFor counts the validity bitmap even
+            // when every value is non-null.
+            bytes = bytes.saturating_add(length.div_ceil(8));
+        }
+        Ok(bytes)
+    }
+
+    fn next_batch_length(
+        args: &[Vec<ArrayRef>],
+        offset: usize,
+        remaining: usize,
+        max_records: usize,
+        max_bytes: usize,
+    ) -> Result<usize> {
+        let limit = if max_records == 0 {
+            remaining
+        } else {
+            remaining.min(max_records)
+        };
+        if limit == 0 || max_bytes == 0 || args.iter().all(Vec::is_empty) {
+            return Ok(limit);
+        }
+        if Self::input_bytes(args, offset, limit)? < max_bytes {
+            return Ok(limit);
+        }
+        let (mut low, mut high) = (1, limit);
+        while low < high {
+            let middle = low + (high - low) / 2;
+            if Self::input_bytes(args, offset, middle)? >= max_bytes {
+                high = middle;
+            } else {
+                low = middle + 1;
+            }
+        }
+        Ok(low)
+    }
+
+    fn evaluate_batch(
+        specs: &[ArrowPythonUdfSpec],
+        workers: &[ArrowPythonUdf],
+        schema: SchemaRef,
+        batch: &RecordBatch,
+        args: &[Vec<ArrayRef>],
+        offset: usize,
+        length: usize,
+    ) -> Result<RecordBatch> {
+        let mut columns = batch.slice(offset, length).columns().to_vec();
+        for ((spec, worker), function_args) in 
specs.iter().zip(workers).zip(args) {
+            let sliced_args: Vec<_> = function_args
+                .iter()
+                .map(|array| array.slice(offset, length))
+                .collect();
+            columns.push(worker.evaluate_named(&sliced_args, &spec.arg_names, 
length)?);
+        }
+        Ok(RecordBatch::try_new(schema, columns)?)
+    }
+}
+
+impl DisplayAs for ArrowPythonUdfExec {
+    fn fmt_as(&self, t: DisplayFormatType, f: &mut Formatter) -> 
std::fmt::Result {
+        match t {
+            DisplayFormatType::Default
+            | DisplayFormatType::Verbose
+            | DisplayFormatType::TreeRender => {
+                write!(f, "CometArrowPythonUdfExec: {} UDF(s)", 
self.specs.len())
+            }
+        }
+    }
+}
+
+impl ExecutionPlan for ArrowPythonUdfExec {
+    fn name(&self) -> &str {
+        "CometArrowPythonUdfExec"
+    }
+
+    fn schema(&self) -> SchemaRef {
+        Arc::clone(&self.schema)
+    }
+
+    fn properties(&self) -> &Arc<PlanProperties> {
+        &self.cache
+    }
+
+    fn children(&self) -> Vec<&Arc<dyn ExecutionPlan>> {
+        vec![&self.child]
+    }
+
+    fn apply_expressions(
+        &self,
+        f: &mut dyn FnMut(&Arc<dyn PhysicalExpr>) -> Result<TreeNodeRecursion>,
+    ) -> Result<TreeNodeRecursion> {
+        apply_expression_roots(self.specs.iter().flat_map(|spec| 
spec.args.iter()), f)
+    }
+
+    fn with_new_children(
+        self: Arc<Self>,
+        children: Vec<Arc<dyn ExecutionPlan>>,
+    ) -> Result<Arc<dyn ExecutionPlan>> {
+        if children.len() != 1 {
+            return exec_err!("ArrowPythonUdfExec requires exactly one child");
+        }
+        Ok(Arc::new(Self::try_new(
+            Arc::clone(&children[0]),
+            self.specs.clone(),
+            self.max_records_per_batch as i32,
+            self.max_bytes_per_batch as i64,
+        )?))
+    }
+
+    fn execute(
+        &self,
+        partition: usize,
+        context: Arc<TaskContext>,
+    ) -> Result<SendableRecordBatchStream> {
+        let input = self.child.execute(partition, context)?;
+        let workers: Vec<_> = self
+            .specs
+            .iter()
+            .map(|spec| {
+                ArrowPythonUdf::from_command(
+                    &spec.command,
+                    spec.return_type.clone(),
+                    true,
+                    true,
+                    &spec.python_version,
+                )
+            })
+            .collect::<std::result::Result<_, _>>()?;
+        let workers = Arc::new(workers);
+        let specs = Arc::new(self.specs.clone());
+        let schema = Arc::clone(&self.schema);
+        let max_records_per_batch = self.max_records_per_batch;
+        let max_bytes_per_batch = self.max_bytes_per_batch;
+        let stream = input.flat_map(move |batch| {
+            let workers = Arc::clone(&workers);
+            let specs = Arc::clone(&specs);
+            let schema = Arc::clone(&schema);
+            let (batch, args, mut error) = match batch {
+                // Spark's Arrow writer does not invoke a scalar UDF for an 
empty input
+                // batch. Native scans may still emit one, so skip it before 
evaluating
+                // arguments or entering Python.
+                Ok(batch) if batch.num_rows() == 0 => (None, None, None),
+                Ok(batch) => {
+                    match tokio::task::block_in_place(|| 
Self::evaluate_args(&specs, &batch)) {
+                        Ok(args) => (Some(batch), Some(args), None),
+                        Err(error) => (None, None, Some(error)),
+                    }
+                }
+                Err(error) => (None, None, Some(error)),
+            };
+            let mut offset = 0;
+            let mut failed = false;
+            // RecordBatch::slice shares Arrow buffers. Produce one result per 
poll
+            // so the remaining slices do not pin a second set of output 
batches.
+            stream::iter(std::iter::from_fn(move || {
+                if let Some(error) = error.take() {
+                    return Some(Err(error));
+                }
+                if failed {
+                    return None;
+                }
+                let batch = batch.as_ref()?;
+                let args = args.as_ref()?;
+                if offset == batch.num_rows() {
+                    return None;
+                }
+                let length = match Self::next_batch_length(
+                    args,
+                    offset,
+                    batch.num_rows() - offset,
+                    max_records_per_batch,
+                    max_bytes_per_batch,
+                ) {
+                    Ok(length) => length,
+                    Err(error) => {
+                        failed = true;
+                        return Some(Err(error));
+                    }
+                };
+                // Keep the JVM scan path synchronous so its Pending loop does 
not spin while
+                // Python runs. On a tokio worker, this hands its other tasks 
to another worker.
+                let result = tokio::task::block_in_place(|| {

Review Comment:
   Nothing interrupts it today. The limitations section in `794b2767f` now says 
that killing a task does not stop a running Python call: a cancelled job or the 
losing copy of a speculative task keeps its core and competes for the GIL until 
the UDF returns. Interrupting the call, for example with 
`PyThreadState_SetAsyncExc`, is tracked in #6811, and we'll start on it once 
this PR is merged.



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