[SPARK-11655][CORE] Fix deadlock in handling of launcher stop().

The stop() callback was trying to close the launcher connection in the
same thread that handles connection data, which ended up causing a
deadlock. So avoid that by dispatching the stop() request in its own
thread.

On top of that, add some exception safety to a few parts of the code,
and use "destroyForcibly" from Java 8 if it's available, to force
kill the child process. The flip side is that "kill()" may not actually
work if running Java 7.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #9633 from vanzin/SPARK-11655.

2 files changed, 18 insertions, 2 deletions

diff --git a/launcher/src/main/java/org/apache/spark/launcher/ChildProcAppHandle.java b/launcher/src/main/java/org/apache/spark/launcher/ChildProcAppHandle.java
index de50f14fbd..1bfda289de 100644
--- a/launcher/src/main/java/org/apache/spark/launcher/ChildProcAppHandle.java
+++ b/launcher/src/main/java/org/apache/spark/launcher/ChildProcAppHandle.java
@@ -18,6 +18,7 @@
 package org.apache.spark.launcher;
 
 import java.io.IOException;
+import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.ThreadFactory;
@@ -102,8 +103,20 @@ class ChildProcAppHandle implements SparkAppHandle {
       disconnect();
     }
     if (childProc != null) {
-      childProc.destroy();
-      childProc = null;
+      try {
+        childProc.exitValue();
+      } catch (IllegalThreadStateException e) {
+        // Child is still alive. Try to use Java 8's "destroyForcibly()" if available,
+        // fall back to the old API if it's not there.
+        try {
+          Method destroy = childProc.getClass().getMethod("destroyForcibly");
+          destroy.invoke(childProc);
+        } catch (Exception inner) {
+          childProc.destroy();
+        }
+      } finally {
+        childProc = null;
+      }
     }
   }
 
diff --git a/launcher/src/main/java/org/apache/spark/launcher/SparkAppHandle.java b/launcher/src/main/java/org/apache/spark/launcher/SparkAppHandle.java
index 13dd9f1739..e9caf0b3cb 100644
--- a/launcher/src/main/java/org/apache/spark/launcher/SparkAppHandle.java
+++ b/launcher/src/main/java/org/apache/spark/launcher/SparkAppHandle.java
@@ -89,6 +89,9 @@ public interface SparkAppHandle {
    * Tries to kill the underlying application. Implies {@link #disconnect()}. This will not send
    * a {@link #stop()} message to the application, so it's recommended that users first try to
    * stop the application cleanly and only resort to this method if that fails.
+   * <p>
+   * Note that if the application is running as a child process, this method fail to kill the
+   * process when using Java 7. This may happen if, for example, the application is deadlocked.
    */
   void kill();