[SPARK-4301] StreamingContext should not allow start() to be called after calling stop()

streaming/src/main/scala/org/apache/spark/streaming/StreamingContext.scala

@@ -436,10 +436,10 @@ class StreamingContext private[streaming] (
 
   /**
    * Start the execution of the streams.
+   *
+   * @throws SparkException if the context has already been started or stopped.
    */
   def start(): Unit = synchronized {
-    // Throw exception if the context has already been started once
-    // or if a stopped context is being started again
     if (state == Started) {
       throw new SparkException("StreamingContext has already been started")
     }
@@ -472,8 +472,9 @@ class StreamingContext private[streaming] (
   /**
    * Stop the execution of the streams immediately (does not wait for all received data
    * to be processed).
-   * @param stopSparkContext Stop the associated SparkContext or not
    *
+   * @param stopSparkContext if true, stops the associated SparkContext. The SparkContext will be
+   *                         stopped regardless of whether this StreamingContext has been started.
    */
   def stop(stopSparkContext: Boolean = true): Unit = synchronized {
     stop(stopSparkContext, false)
@@ -482,25 +483,27 @@ class StreamingContext private[streaming] (
   /**
    * Stop the execution of the streams, with option of ensuring all received data
    * has been processed.
-   * @param stopSparkContext Stop the associated SparkContext or not
-   * @param stopGracefully Stop gracefully by waiting for the processing of all
+   *
+   * @param stopSparkContext if true, stops the associated SparkContext. The SparkContext will be
+   *                         stopped regardless of whether this StreamingContext has been started.
+   * @param stopGracefully if true, stops gracefully by waiting for the processing of all
    *                       received data to be completed
    */
   def stop(stopSparkContext: Boolean, stopGracefully: Boolean): Unit = synchronized {
-    // Warn (but not fail) if context is stopped twice,
-    // or context is stopped before starting
-    if (state == Initialized) {
-      logWarning("StreamingContext has not been started yet")
-      return
-    }
     if (state == Stopped) {
       logWarning("StreamingContext has already been stopped")
-      return
-    } // no need to throw an exception as its okay to stop twice
-    scheduler.stop(stopGracefully)
-    logInfo("StreamingContext stopped successfully")
-    waiter.notifyStop()
-    if (stopSparkContext) sc.stop()
+    } else {
+      // Even if the streaming context has not been started, we still need to stop the SparkContext:
+      if (stopSparkContext) sc.stop()
+      if (state == Initialized) {
+        logWarning("StreamingContext has not been started yet")
+      } else {
+        scheduler.stop(stopGracefully)
+        logInfo("StreamingContext stopped successfully")
+        waiter.notifyStop()
+      }
+    }
+    // The state should always be Stopped after calling `stop()`, even if we haven't started yet:
     state = Stopped
   }
 }

streaming/src/test/scala/org/apache/spark/streaming/StreamingContextSuite.scala

@@ -46,10 +46,6 @@ class StreamingContextSuite extends FunSuite with BeforeAndAfter with Timeouts w
   after {
     if (ssc != null) {
       ssc.stop()
-      if (ssc.sc != null) {
-        // Calling ssc.stop() does not always stop the associated SparkContext.
-        ssc.sc.stop()
-      }
       ssc = null
     }
     if (sc != null) {
@@ -137,11 +133,16 @@ class StreamingContextSuite extends FunSuite with BeforeAndAfter with Timeouts w
     ssc.stop()
   }
 
-  test("stop before start and start after stop") {
+  test("stop before start") {
     ssc = new StreamingContext(master, appName, batchDuration)
     addInputStream(ssc).register()
     ssc.stop()  // stop before start should not throw exception
-    ssc.start()
+  }
+
+  test("start after stop") {
+    // Regression test for SPARK-4301
+    ssc = new StreamingContext(master, appName, batchDuration)
+    addInputStream(ssc).register()
     ssc.stop()
     intercept[SparkException] {
       ssc.start() // start after stop should throw exception