Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/19519#discussion_r146332249
--- Diff:
core/src/main/scala/org/apache/spark/deploy/SparkApplication.scala ---
@@ -0,0 +1,55 @@
+/*
+ * 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.deploy
+
+import java.lang.reflect.Modifier
+
+import org.apache.spark.SparkConf
+
+/**
+ * Entry point for a Spark application. Implementations must provide a
no-argument constructor.
+ */
+private[spark] trait SparkApplication {
+
+ def start(args: Array[String], conf: SparkConf): Unit
+
+}
+
+/**
+ * Implementation of SparkApplication that wraps a standard Java class
with a "main" method.
+ *
+ * Configuration is propagated to the application via system properties,
so running multiple
+ * of these in the same JVM may lead to undefined behavior due to
configuration leaks.
+ */
+private[deploy] class JavaMainApplication(klass: Class[_]) extends
SparkApplication {
+
+ override def start(args: Array[String], conf: SparkConf): Unit = {
+ val mainMethod = klass.getMethod("main", new Array[String](0).getClass)
+ if (!Modifier.isStatic(mainMethod.getModifiers)) {
+ throw new IllegalStateException("The main method in the given main
class must be static")
+ }
+
+ val sysProps = conf.getAll.toMap
+ sysProps.foreach { case (k, v) =>
+ sys.props(k) = v
+ }
+
+ mainMethod.invoke(null, args)
+ }
--- End diff --
That's dangerous, because you don't know what the user code is doing. What
if it spawn a thread and that separate thread creates the `SparkContext`? Then
you may be clearing system properties before the user app had the chance to
read them.
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