code review request for deadlock detection fix (8007476) (original) (raw)

David Holmes david.holmes at oracle.com
Wed Feb 27 17:40:39 PST 2013

Hi Dan,

This looks fine to me. I'm a little nervous the removal of the asserts as we should detect when an owning thread disappears as it is a major problem. But if those asserts are only in the diagnostic paths then it is better to let the diagnostics complete as you have done.

On 28/02/2013 12:52 AM, Karen Kinnear wrote:

Code looks good. I did not study the details (again) for the monitor owner, but my memory is that there are other cases in which the monitor owner can be temporarily null, so this is will help there also.

Karen, it isn't that the monitor owner is temporarily null, but that the thread associated with an owned monitor can not be found. That should never happen. Whenever a monitor has an owner the "owner" information should lead to a live thread.

David

thanks, Karen On Feb 26, 2013, at 6:54 PM, Daniel D. Daugherty wrote:

Greetings,

I have a fix to make deadlock detection a little more robust in the case of being unable to find the JavaThread associated with an object lock: 8007476 assert(theowner != NULL) failed: Did not find owning Java thread for lock word address http://bugs.sun.com/bugdatabase/viewbug.do?bugid=8007476 https://jbs.oracle.com/bugs/browse/JDK-8007476 Yes, I know that's not supposed to happen, but if and when it does happen, it would be good to be able to diagnose the VM to try and figure out what the heck happened. Here is the webrev URL: http://cr.openjdk.java.net/~dcubed/8007476-webrev/0-hsx25/ There is some sample output in the bug report that shows both regular deadlock detection output and the proposed modified deadlock detection output. Thanks, in advance, for any comments, suggestions or questions. Dan P.S. Yes, I've included a bit of tweaking to JVM/TI code to deal with invalid assertion failures that are discussed in the following bug: 6786879 Race in jvmti GetObjectMonitorUsage could lead to crashes http://bugs.sun.com/bugdatabase/viewbug.do?bugid=6786879 https://jbs.oracle.com/bugs/browse/JDK-6786879 However, I haven't tried to address all the races that are discussed in that bug including the race in the call to JvmtiEnv::isthreadfullysuspended() where the underlying call to JavaThread::waitforextsuspendcompletion() can crash on lock exit. Yikes, that one is nasty.

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