[SPARK-6492][CORE] SparkContext.stop() can deadlock when DAGSchedulerEventProcessLoop dies

I've added a timeout and retry loop around the SparkContext shutdown code that should fix this deadlock. If a SparkContext shutdown is in progress when another thread comes knocking, it will wait for 10 seconds for the lock, then fall through where the outer loop will re-submit the request.

Author: Ilya Ganelin <ilya.ganelin@capitalone.com>

Closes #5277 from ilganeli/SPARK-6492 and squashes the following commits:

8617a7e [Ilya Ganelin] Resolved merge conflict
2fbab66 [Ilya Ganelin] Added MIMA Exclude
a0e2c70 [Ilya Ganelin] Deleted stale imports
fa28ce7 [Ilya Ganelin] reverted to just having a single stopped
76fc825 [Ilya Ganelin] Updated to use atomic booleans instead of the synchronized vars
6e8a7f7 [Ilya Ganelin] Removing unecessary null check for now since i'm not fixing stop ordering yet
cdf7073 [Ilya Ganelin] [SPARK-6492] Moved stopped=true back to the start of the shutdown sequence so this can be addressed in a seperate PR
7fb795b [Ilya Ganelin] Spacing
b7a0c5c [Ilya Ganelin] Import ordering
df8224f [Ilya Ganelin] Added comment for added lock
343cb94 [Ilya Ganelin] [SPARK-6492] Added timeout/retry logic to fix a deadlock in SparkContext shutdown

2 files changed, 34 insertions, 29 deletions

diff --git a/core/src/main/scala/org/apache/spark/SparkContext.scala b/core/src/main/scala/org/apache/spark/SparkContext.scala
index 5b3778ead6..abf81e312d 100644
--- a/core/src/main/scala/org/apache/spark/SparkContext.scala
+++ b/core/src/main/scala/org/apache/spark/SparkContext.scala
@@ -23,7 +23,7 @@ import java.io._
 import java.lang.reflect.Constructor
 import java.net.URI
 import java.util.{Arrays, Properties, UUID}
-import java.util.concurrent.atomic.AtomicInteger
+import java.util.concurrent.atomic.{AtomicBoolean, AtomicInteger}
 import java.util.UUID.randomUUID
 
 import scala.collection.{Map, Set}
@@ -95,10 +95,10 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
 
   val startTime = System.currentTimeMillis()
 
-  @volatile private var stopped: Boolean = false
+  private val stopped: AtomicBoolean = new AtomicBoolean(false)
 
   private def assertNotStopped(): Unit = {
-    if (stopped) {
+    if (stopped.get()) {
       throw new IllegalStateException("Cannot call methods on a stopped SparkContext")
     }
   }
@@ -1390,33 +1390,34 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
     addedJars.clear()
   }
 
-  /** Shut down the SparkContext. */
+  // Shut down the SparkContext.
   def stop() {
-    SparkContext.SPARK_CONTEXT_CONSTRUCTOR_LOCK.synchronized {
-      if (!stopped) {
-        stopped = true
-        postApplicationEnd()
-        ui.foreach(_.stop())
-        env.metricsSystem.report()
-        metadataCleaner.cancel()
-        cleaner.foreach(_.stop())
-        executorAllocationManager.foreach(_.stop())
-        dagScheduler.stop()
-        dagScheduler = null
-        listenerBus.stop()
-        eventLogger.foreach(_.stop())
-        env.actorSystem.stop(heartbeatReceiver)
-        progressBar.foreach(_.stop())
-        taskScheduler = null
-        // TODO: Cache.stop()?
-        env.stop()
-        SparkEnv.set(null)
-        logInfo("Successfully stopped SparkContext")
-        SparkContext.clearActiveContext()
-      } else {
-        logInfo("SparkContext already stopped")
-      }
+    // Use the stopping variable to ensure no contention for the stop scenario.
+    // Still track the stopped variable for use elsewhere in the code.
+    
+    if (!stopped.compareAndSet(false, true)) {
+      logInfo("SparkContext already stopped.")
+      return
     }
+    
+    postApplicationEnd()
+    ui.foreach(_.stop())
+    env.metricsSystem.report()
+    metadataCleaner.cancel()
+    cleaner.foreach(_.stop()) 
+    executorAllocationManager.foreach(_.stop())
+    dagScheduler.stop()
+    dagScheduler = null
+    listenerBus.stop()
+    eventLogger.foreach(_.stop())
+    env.actorSystem.stop(heartbeatReceiver)
+    progressBar.foreach(_.stop())
+    taskScheduler = null
+    // TODO: Cache.stop()?
+    env.stop()
+    SparkEnv.set(null)
+    SparkContext.clearActiveContext()
+    logInfo("Successfully stopped SparkContext")
   }
 
 
@@ -1478,7 +1479,7 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
       partitions: Seq[Int],
       allowLocal: Boolean,
       resultHandler: (Int, U) => Unit) {
-    if (stopped) {
+    if (stopped.get()) {
       throw new IllegalStateException("SparkContext has been shutdown")
     }
     val callSite = getCallSite
diff --git a/project/MimaExcludes.scala b/project/MimaExcludes.scala
index 54500f7c27..c2d828f982 100644
--- a/project/MimaExcludes.scala
+++ b/project/MimaExcludes.scala
@@ -60,6 +60,10 @@ object MimaExcludes {
           ) ++ Seq(
             // SPARK-6510 Add a Graph#minus method acting as Set#difference
             ProblemFilters.exclude[MissingMethodProblem]("org.apache.spark.graphx.VertexRDD.minus")
+          ) ++ Seq(
+            // SPARK-6492 Fix deadlock in SparkContext.stop()
+            ProblemFilters.exclude[MissingMethodProblem]("org.apache.spark.SparkContext.org$" +
+                "apache$spark$SparkContext$$SPARK_CONTEXT_CONSTRUCTOR_LOCK")
           )
 
         case v if v.startsWith("1.3") =>