URGENT RFR (S): fix for Test8004741.java crashes with SIGSEGV in JDK10-hs nightly (8185273)

[Aleksey Shipilev]

On 07/31/2017 04:24 PM, Daniel D. Daugherty wrote:
> Greetings,
> 
> I have a fix for the following P1 JDK10-hs integration_blocker bug:
> 
>     8185273 Test8004741.java crashes with SIGSEGV in JDK10-hs nightly
>     https://bugs.openjdk.java.net/browse/JDK-8185273
> 
> The fix is 2 lines and the comment describing the fix is 4 lines:
> 
> src/share/vm/runtime/thread.cpp:
> 
> L3388: void Threads::parallel_java_threads_do(ThreadClosure* tc) {
> <snip>
> L3395:   // This function is used by ParallelSPCleanupTask in safepoint.cpp
> L3396:   // for cleaning up JavaThreads, but we have to keep the VMThread's
> L3397:   // _oops_do_parity field in sync so we don't miss a parallel GC on
> L3398:   // the VMThread.
> L3399:   VMThread* vmt = VMThread::vm_thread();
> L3400:   (void)vmt->claim_oops_do(true, cp);
> 
> I'm also including some new logging for the VMThread (tag == 'vmthread')
> that came in useful during this bug hunt. Lastly, I've fixed a few minor
> typos that I ran across in the areas where I was hunting.
> 
> Webrev URL: http://cr.openjdk.java.net/~dcubed/8185273-webrev/0/

Those changes make sense, thanks.

It is probably worth mentioning that Threads::parallel_java_threads_do should be in sync with
Threads::possibly_parallel_oops_do? It gets easier to point out the symmetry: possibly_parallel_...
claims all Java threads and the VMThread, so this should also claim the VMThread.

-Aleksey