[SPARK-28917][CORE] Synchronize access to RDD mutable state

RDD dependencies and partitions can be simultaneously
accessed and mutated by user threads and spark's scheduler threads, so
access must be thread-safe.  In particular, as partitions and
dependencies are lazily-initialized, before this change they could get
initialized multiple times, which would lead to the scheduler having an
inconsistent view of the pendings stages and get stuck.

Tested with existing unit tests.

Closes apache#25951 from squito/SPARK-28917.

Authored-by: Imran Rashid <[email protected]>
Signed-off-by: Marcelo Vanzin <[email protected]>

Author: squito

core/src/main/scala/org/apache/spark/rdd/RDD.scala

@@ -225,10 +225,24 @@ abstract class RDD[T: ClassTag](
   /** Get the RDD's current storage level, or StorageLevel.NONE if none is set. */
   def getStorageLevel: StorageLevel = storageLevel
 
+  /**
+   * Lock for all mutable state of this RDD (persistence, partitions, dependencies, etc.).  We do
+   * not use `this` because RDDs are user-visible, so users might have added their own locking on
+   * RDDs; sharing that could lead to a deadlock.
+   *
+   * One thread might hold the lock on many of these, for a chain of RDD dependencies; but
+   * because DAGs are acyclic, and we only ever hold locks for one path in that DAG, there is no
+   * chance of deadlock.
+   *
+   * The use of Integer is simply so this is serializable -- executors may reference the shared
+   * fields (though they should never mutate them, that only happens on the driver).
+   */
+  private val stateLock = new Integer(0)
+
   // Our dependencies and partitions will be gotten by calling subclass's methods below, and will
   // be overwritten when we're checkpointed
-  private var dependencies_ : Seq[Dependency[_]] = _
-  @transient private var partitions_ : Array[Partition] = _
+  @volatile private var dependencies_ : Seq[Dependency[_]] = _
+  @volatile @transient private var partitions_ : Array[Partition] = _
 
   /** An Option holding our checkpoint RDD, if we are checkpointed */
   private def checkpointRDD: Option[CheckpointRDD[T]] = checkpointData.flatMap(_.checkpointRDD)
@@ -240,7 +254,11 @@ abstract class RDD[T: ClassTag](
   final def dependencies: Seq[Dependency[_]] = {
     checkpointRDD.map(r => List(new OneToOneDependency(r))).getOrElse {
       if (dependencies_ == null) {
-        dependencies_ = getDependencies
+        stateLock.synchronized {
+          if (dependencies_ == null) {
+            dependencies_ = getDependencies
+          }
+        }
       }
       dependencies_
     }
@@ -253,10 +271,14 @@ abstract class RDD[T: ClassTag](
   final def partitions: Array[Partition] = {
     checkpointRDD.map(_.partitions).getOrElse {
       if (partitions_ == null) {
-        partitions_ = getPartitions
-        partitions_.zipWithIndex.foreach { case (partition, index) =>
-          require(partition.index == index,
-            s"partitions($index).partition == ${partition.index}, but it should equal $index")
+        stateLock.synchronized {
+          if (partitions_ == null) {
+            partitions_ = getPartitions
+            partitions_.zipWithIndex.foreach { case (partition, index) =>
+              require(partition.index == index,
+                s"partitions($index).partition == ${partition.index}, but it should equal $index")
+            }
+          }
         }
       }
       partitions_
@@ -1788,7 +1810,7 @@ abstract class RDD[T: ClassTag](
    * Changes the dependencies of this RDD from its original parents to a new RDD (`newRDD`)
    * created from the checkpoint file, and forget its old dependencies and partitions.
    */
-  private[spark] def markCheckpointed(): Unit = {
+  private[spark] def markCheckpointed(): Unit = stateLock.synchronized {
     clearDependencies()
     partitions_ = null
     deps = null    // Forget the constructor argument for dependencies too
@@ -1800,7 +1822,7 @@ abstract class RDD[T: ClassTag](
    * collected. Subclasses of RDD may override this method for implementing their own cleaning
    * logic. See [[org.apache.spark.rdd.UnionRDD]] for an example.
    */
-  protected def clearDependencies(): Unit = {
+  protected def clearDependencies(): Unit = stateLock.synchronized {
     dependencies_ = null
   }
 
@@ -1959,6 +1981,7 @@ abstract class RDD[T: ClassTag](
       deterministicLevelCandidates.maxBy(_.id)
     }
   }
+
 }
 
 

core/src/main/scala/org/apache/spark/scheduler/DAGScheduler.scala

@@ -400,7 +400,8 @@ private[spark] class DAGScheduler(
     if (!mapOutputTracker.containsShuffle(shuffleDep.shuffleId)) {
       // Kind of ugly: need to register RDDs with the cache and map output tracker here
       // since we can't do it in the RDD constructor because # of partitions is unknown
-      logInfo("Registering RDD " + rdd.id + " (" + rdd.getCreationSite + ")")
+      logInfo(s"Registering RDD ${rdd.id} (${rdd.getCreationSite}) as input to " +
+        s"shuffle ${shuffleDep.shuffleId}")
       mapOutputTracker.registerShuffle(shuffleDep.shuffleId, rdd.partitions.length)
     }
     stage
@@ -1080,7 +1081,8 @@ private[spark] class DAGScheduler(
   private def submitStage(stage: Stage): Unit = {
     val jobId = activeJobForStage(stage)
     if (jobId.isDefined) {
-      logDebug("submitStage(" + stage + ")")
+      logDebug(s"submitStage($stage (name=${stage.name};" +
+        s"jobs=${stage.jobIds.toSeq.sorted.mkString(",")}))")
       if (!waitingStages(stage) && !runningStages(stage) && !failedStages(stage)) {
         val missing = getMissingParentStages(stage).sortBy(_.id)
         logDebug("missing: " + missing)

core/src/test/scala/org/apache/spark/DistributedSuite.scala

@@ -339,6 +339,21 @@ class DistributedSuite extends SparkFunSuite with Matchers with LocalSparkContex
     }
   }
 
+  test("reference partitions inside a task") {
+    // Run a simple job which just makes sure there is no failure if we touch rdd.partitions
+    // inside a task.  This requires the stateLock to be serializable.  This is very convoluted
+    // use case, it's just a check for backwards-compatibility after the fix for SPARK-28917.
+    sc = new SparkContext("local-cluster[1,1,1024]", "test")
+    val rdd1 = sc.parallelize(1 to 10, 1)
+    val rdd2 = rdd1.map { x => x + 1}
+    // ensure we can force computation of rdd2.dependencies inside a task.  Just touching
+    // it will force computation and touching the stateLock.  The check for null is to just
+    // to make sure that we've setup our test correctly, and haven't precomputed dependencies
+    // in the driver
+    val dependencyComputeCount = rdd1.map { x => if (rdd2.dependencies == null) 1 else 0}.sum()
+    assert(dependencyComputeCount > 0)
+  }
+
 }
 
 object DistributedSuite {