[SPARK-18113] Use ask to replace askWithRetry in canCommit and make receiver idempotent.

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

@@ -22,6 +22,7 @@ import scala.collection.mutable
 import org.apache.spark._
 import org.apache.spark.internal.Logging
 import org.apache.spark.rpc.{RpcCallContext, RpcEndpoint, RpcEndpointRef, RpcEnv}
+import org.apache.spark.util.{RpcUtils, ThreadUtils}
 
 private sealed trait OutputCommitCoordinationMessage extends Serializable
 
@@ -88,7 +89,8 @@ private[spark] class OutputCommitCoordinator(conf: SparkConf, isDriver: Boolean)
     val msg = AskPermissionToCommitOutput(stage, partition, attemptNumber)
     coordinatorRef match {
       case Some(endpointRef) =>
-        endpointRef.askWithRetry[Boolean](msg)
+        ThreadUtils.awaitResult(endpointRef.ask[Boolean](msg),
+          RpcUtils.askRpcTimeout(conf).duration)
       case None =>
         logError(
           "canCommit called after coordinator was stopped (is SparkEnv shutdown in progress)?")
@@ -165,9 +167,18 @@ private[spark] class OutputCommitCoordinator(conf: SparkConf, isDriver: Boolean)
             authorizedCommitters(partition) = attemptNumber
             true
           case existingCommitter =>
-            logDebug(s"Denying attemptNumber=$attemptNumber to commit for stage=$stage, " +
-              s"partition=$partition; existingCommitter = $existingCommitter")
-            false
+            // Coordinator should be idempotent when receiving AskPermissionToCommit.
+            if (existingCommitter == attemptNumber) {
+              logWarning(s"Authorizing duplicate request to commit for " +
+                s"attemptNumber=$attemptNumber to commit for stage=$stage," +
+                s" partition=$partition; existingCommitter = $existingCommitter." +
+                s" This can indicate dropped network traffic.")
+              true
+            } else {
+              logDebug(s"Denying attemptNumber=$attemptNumber to commit for stage=$stage, " +
+                s"partition=$partition; existingCommitter = $existingCommitter")
+              false
+            }
         }
       case None =>
         logDebug(s"Stage $stage has completed, so not allowing attempt number $attemptNumber of" +

core/src/test/scala/org/apache/spark/scheduler/OutputCommitCoordinatorSuite.scala

@@ -189,6 +189,12 @@ class OutputCommitCoordinatorSuite extends SparkFunSuite with BeforeAndAfter {
     assert(
       !outputCommitCoordinator.canCommit(stage, partition, nonAuthorizedCommitter + 3))
   }
+
+  test("Duplicate calls to canCommit from the authorized committer gets idempotent responses.") {
+    val rdd = sc.parallelize(Seq(1), 1)
+    sc.runJob(rdd, OutputCommitFunctions(tempDir.getAbsolutePath).callCanCommitMultipleTimes _,
+       0 until rdd.partitions.size)
+  }
 }
 
 /**
@@ -221,6 +227,16 @@ private case class OutputCommitFunctions(tempDirPath: String) {
       if (ctx.attemptNumber == 0) failingOutputCommitter else successfulOutputCommitter)
   }
 
+  // Receiver should be idempotent for AskPermissionToCommitOutput
+  def callCanCommitMultipleTimes(iter: Iterator[Int]): Unit = {
+    val ctx = TaskContext.get()
+    val canCommit1 = SparkEnv.get.outputCommitCoordinator
+      .canCommit(ctx.stageId(), ctx.partitionId(), ctx.attemptNumber())
+    val canCommit2 = SparkEnv.get.outputCommitCoordinator
+      .canCommit(ctx.stageId(), ctx.partitionId(), ctx.attemptNumber())
+    assert(canCommit1 && canCommit2)
+  }
+
   private def runCommitWithProvidedCommitter(
       ctx: TaskContext,
       iter: Iterator[Int],