Timer thread termination may not be detected and cause non-clean VM shutdown (original) (raw)

Jing LV lvjing at linux.vnet.ibm.com
Tue Sep 13 07:51:29 UTC 2011

Hello,

I've meet a subtle issue with Timer. As we know, every Timer objects spawn a new thread (which is optionally a daemon thread). On VM shutdown, there is no way to ensure that the daemon thread terminates (cancel() and purge() only clear the queue). This can lead to non-clean VM shutdown (return non-zero exit code) and has caused problems in some applications especailly with attach API. Further, there is no way to determine when all tasks have completed after calling cancel(). This problem was encouraged to occur when the test machine was busy. The original failure occurs when created & destroyed 15 processes with 1 JVM's each (via JNI). It seems all versions of JDK has this issue. I was trying to make a simple testcase but no much progress - though logically I guess everyone can understand this easily. Current my workaround is to have some thread to join the Timer thread to wait its termination - but it seems have some side effect and cause problems.

A quick idea to resolve the problem completely is to add a new API like "public void cancel(boolean wait)" to indicate if we will wait for the Timer threads to be terminated, or add some private methods to help the VM to do something to terminate the Timer.

Any suggestions/comments? Thanks.

-- Best Regards, Jimmy, Jing LV

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