Member Avatar for xeon123

Hi,

I'm iterating an Arraylist inside a synchronized method, and I've set the Arraylist synchronized inside the method, but I still got the error ConcurrentModificationException. Why this is happening?

private synchronized TaskInProgress findTaskFromList(
			Collection<TaskInProgress> tips, 
			TaskTrackerStatus ttStatus,
			int numUniqueHosts,
			boolean removeFailedTip) {

		synchronized(tips) {
			Iterator<TaskInProgress> iter = tips.iterator();

			while (iter.hasNext()) {
				TaskInProgress tip = iter.next();
                        }
               }
}
java.io.IOException: java.util.ConcurrentModificationException
        at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
        at java.util.AbstractList$Itr.next(AbstractList.java:343)
        at org.apache.hadoop.mapred.JobInProgress.findTaskFromList(JobInProgress.java:1930)
        at org.apache.hadoop.mapred.JobInProgress.findNewMapTask(JobInProgress.java:2143)
        at org.apache.hadoop.mapred.JobInProgress.obtainNewLocalMapTask(JobInProgress.java:1268)
        at org.apache.hadoop.mapred.JobQueueTaskScheduler.assignTasks(JobQueueTaskScheduler.java:163)
        at org.apache.hadoop.mapred.JobTracker.heartbeat(JobTracker.java:2576)
        at sun.reflect.GeneratedMethodAccessor4.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:955)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:396)
        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:953)

Thanks,

Edited by xeon123 because: n/a
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  • Latest Post Latest Post by masijade
Member Avatar for masijade

Okay? And when something else uses that list without synchronizing on it (or the instance)? That is where the problem is coming from.

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