[concurrency-interest] LinkedBlockingDeque deadlock? (Test case) (original) (raw)

David Holmes - Sun Microsystems David.Holmes at Sun.COM
Thu Jul 23 05:48:31 UTC 2009

Just an update.

The good news is that I managed to reproduce this on an 8-way Intel box. Sometimes it hangs due to the applications LinkedBlockingDeque and sometimes it hangs in the executor's LinkedBlockingQueue.

The bad news is that as soon as I modified the LBQ/LBD and ReentrantLock code to allow me to probe deeper, I can no longer reproduce the problem :-( And all I did to the code was make everything public so that I could dump the lock state when the hang occurred.

Very frustrating ...

David

David Holmes said the following on 07/18/09 12:28:

Sorry Ryan, misread the stack trace. The main thread is interacting with the executors LBQ not the application one.

I'll see if I can use this test to reproduce the issue on Monday. David Holmes

-----Original Message----- From: concurrency-interest-bounces at cs.oswego.edu [mailto:concurrency-interest-bounces at cs.oswego.edu]On Behalf Of David Holmes Sent: Saturday, 18 July 2009 12:15 PM To: Ryan Betts; concurrency-interest at cs.oswego.edu Cc: core-libs-dev Subject: Re: [concurrency-interest] LinkedBlockingDeque deadlock? (Test case)

Ryan, Thanks very much for this. When this "deadlocks" does top show whether the java process is actually quiet or is it still consuming CPU? I notice that in the stack dump the main thread is in the process of unlocking the lock that the other threads are waiting upon and hence the system is not deadlocked - unless that main thread is actually "stuck" somewhere. Can you take a series of stackdumps to see if/how the main thread is executing? Feel free to just send them to me rather than the mailing lists. Thanks, David Holmes -----Original Message----- From: concurrency-interest-bounces at cs.oswego.edu [mailto:concurrency-interest-bounces at cs.oswego.edu]On Behalf Of Ryan Betts Sent: Saturday, 18 July 2009 2:48 AM To: concurrency-interest at cs.oswego.edu Cc: core-libs-dev Subject: Re: [concurrency-interest] LinkedBlockingDeque deadlock? (Test case) Hello all, I've been working with Ariel on the j.u.c.LinkedBlockingDeque deadlock we observe. The attached test case reproduces the deadlock intermittently, usually requiring several minutes. The test simply prints periods until it deadlocks. Attempts to produce a simpler test case using only ReentrantLock or without an ExecutorService were unsuccessful. I've attached jstack reports showing the deadlocked case and the dmesg output from one of the servers that reproduces the defect. To date, this deadlock only occurs on our 2 socket i7s. We have not filed a defect with Sun for this issue. If that would be helpful (or necessary), we would of course happily oblige. $ java -version java version "1.6.0" OpenJDK Runtime Environment (build 1.6.0-b09) OpenJDK 64-Bit Server VM (build 1.6.0-b09, mixed mode) $ uname -a Linux host3e 2.6.18-128.1.16.el5 #1 SMP Tue Jun 30 06:07:26 EDT 2009 x8664 x8664 x8664 GNU/Linux $ javac LBDLockPatternTest.java $ java LBDLockPatternTest Thank you, *--Ryan.

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