Make use of the isIdle() method on the TaskTracker

Previously we would check the number of running jobs, however that
sometimes returend incorrect values especially when dealing with
failed jobs on the cluster. The result being some TaskTrackers never
commit suicide.

src/main/java/org/apache/hadoop/mapred/MesosExecutor.java

@@ -14,6 +14,7 @@
 import java.lang.reflect.Field;
 import java.lang.ReflectiveOperationException;
 
+import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
@@ -235,12 +236,12 @@ public void run() {
           return;
         }
 
-        LOG.info("Checking to see if TaskTracker has no running jobs");
-        int runningJobs = taskTracker.runningJobs.size();
+        LOG.info("Checking to see if TaskTracker is idle");
 
-        // Check to see if the number of running jobs on the task tracker is zero
-        if (runningJobs == 0) {
-          LOG.warn("TaskTracker has zero jobs running, terminating");
+        // If the task tracker is idle, all tasks have finished and task output
+        // has been cleaned up.
+        if (taskTracker.isIdle()) {
+          LOG.warn("TaskTracker is idle, terminating");
 
           try {
             taskTracker.shutdown();
@@ -251,7 +252,17 @@ public void run() {
           }
         }
         else {
-          LOG.info("TaskTracker has " + runningJobs + " jobs running");
+          try {
+            Field field = taskTracker.getClass().getDeclaredField("tasksToCleanup");
+            field.setAccessible(true);
+            BlockingQueue<TaskTrackerAction> tasksToCleanup = ((BlockingQueue<TaskTrackerAction>) field.get(taskTracker));
+            LOG.info("TaskTracker has " + taskTracker.tasks.size() +
+                     " running tasks and " + tasksToCleanup +
+                     " tasks to clean up.");
+          } catch (ReflectiveOperationException e) {
+            LOG.fatal("Failed to get task counts from TaskTracker", e);
+          }
+
           scheduleSuicideTimer();
         }
       }