diff --git a/core/src/main/scala/org/apache/spark/scheduler/cluster/StandaloneSchedulerBackend.scala b/core/src/main/scala/org/apache/spark/scheduler/cluster/StandaloneSchedulerBackend.scala
index 7befdb0c1f64d..0529fe9eed4da 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/cluster/StandaloneSchedulerBackend.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/cluster/StandaloneSchedulerBackend.scala
@@ -18,6 +18,7 @@
 package org.apache.spark.scheduler.cluster
 
 import java.util.concurrent.Semaphore
+import java.util.concurrent.atomic.AtomicBoolean
 
 import scala.concurrent.Future
 
@@ -42,7 +43,7 @@ private[spark] class StandaloneSchedulerBackend(
   with Logging {
 
   private var client: StandaloneAppClient = null
-  private var stopping = false
+  private val stopping = new AtomicBoolean(false)
   private val launcherBackend = new LauncherBackend() {
     override protected def onStopRequest(): Unit = stop(SparkAppHandle.State.KILLED)
   }
@@ -112,7 +113,7 @@ private[spark] class StandaloneSchedulerBackend(
     launcherBackend.setState(SparkAppHandle.State.RUNNING)
   }
 
-  override def stop(): Unit = synchronized {
+  override def stop(): Unit = {
     stop(SparkAppHandle.State.FINISHED)
   }
 
@@ -125,14 +126,14 @@ private[spark] class StandaloneSchedulerBackend(
 
   override def disconnected() {
     notifyContext()
-    if (!stopping) {
+    if (!stopping.get) {
       logWarning("Disconnected from Spark cluster! Waiting for reconnection...")
     }
   }
 
   override def dead(reason: String) {
     notifyContext()
-    if (!stopping) {
+    if (!stopping.get) {
       launcherBackend.setState(SparkAppHandle.State.KILLED)
       logError("Application has been killed. Reason: " + reason)
       try {
@@ -206,20 +207,20 @@ private[spark] class StandaloneSchedulerBackend(
     registrationBarrier.release()
   }
 
-  private def stop(finalState: SparkAppHandle.State): Unit = synchronized {
-    try {
-      stopping = true
-
-      super.stop()
-      client.stop()
+  private def stop(finalState: SparkAppHandle.State): Unit = {
+    if (stopping.compareAndSet(false, true)) {
+      try {
+        super.stop()
+        client.stop()
 
-      val callback = shutdownCallback
-      if (callback != null) {
-        callback(this)
+        val callback = shutdownCallback
+        if (callback != null) {
+          callback(this)
+        }
+      } finally {
+        launcherBackend.setState(finalState)
+        launcherBackend.close()
       }
-    } finally {
-      launcherBackend.setState(finalState)
-      launcherBackend.close()
     }
   }