RFR: 8267653: Remove Mutex::_safepoint_check_sometimes [v2]

[Coleen Phillimore]

On Wed, 26 May 2021 00:38:00 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add assert that the thread is terminated before taking Heap_lock
>
> src/hotspot/share/gc/shenandoah/shenandoahReferenceProcessor.cpp line 543:
> 
>> 541:   } else {
>> 542:     // Heap_lock protects external pending list
>> 543:     MonitorLocker ml(Heap_lock);
> 
> For performance you could leave the _no_safepoint_check flag.

I cannot leave it because there's an assert to verify that we don't try to take this lock without a safepoint check, since it was declared with safepoint_check_always.

> src/hotspot/share/runtime/thread.cpp line 3420:
> 
>> 3418:     // we'll never emerge out of the safepoint before the VM exits.
>> 3419: 
>> 3420:     MutexLocker ml(Heap_lock);
> 
> Can you add an assert before this that the thread is_terminated() as that is the key to the mutex acquisition not doing a safepoint check.

Ok, I can add:
+    assert(thread->is_terminated(), "must be terminated before acquiring Heap_lock");
and rerun tests.

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PR: https://git.openjdk.java.net/jdk/pull/4184