(S) RFR: 8159461: bigapps/Kitchensink/stressExitCode hits assert: Must be VMThread or JavaThread

[Frederic Parain]

David,

Interesting twist about JavaThreads returning to their plain
Thread nature before dying.

Fix looks good to me.

Fred

On 08/02/2016 09:13 PM, David Holmes wrote:
> webrev: http://cr.openjdk.java.net/~dholmes/8159461/webrev/
>
> bug: https://bugs.openjdk.java.net/browse/JDK-8159461
>
> The suspend/resume signal (SR_signum) is never sent to a thread once it
> has started to terminate. On one platform (SuSE 12) we have seen what
> appears to be a "stuck" signal, which is only delivered when the
> terminating thread restores its original signal mask (as if
> pthread_sigmask makes the system realize there is a pending signal - we
> already check the signal was not blocked). At this point in the thread
> termination we have freed the osthread, so the the SR_handler would
> access deallocated memory. In debug builds we first hit an assertion
> that the current thread is a JavaThread or the VMThread - that assertion
> fails, even though it is a JavaThread, because we have already executed
> the ~JavaThread destructor and inside the ~Thread destructor we are a
> plain Thread not a JavaThread.
>
> The fix was to make a small adjustment to the thread termination process
> so that we delete the SR_lock before calling os::free_thread(). In the
> SR_handler() we can then use a NULL check of SR_lock() to indicate the
> thread has terminated and we return.
>
> While only seen on Linux I took the opportunity to apply the fix on all
> platforms and also cleaned up the code where we were using
> Thread::current() unsafely in a signal-handling context.
>
> Testing: regular tier 1 (JPRT)
>          Kitchensink (in progress)
>
> As we can't readily reproduce the problem I tested this by having a
> terminating thread raise SR_signum directly from within the ~Thread
> destructor.
>
> Thanks,
> David