RFR: 8253180: ZGC: Implementation of JEP 376: ZGC: Concurrent Thread-Stack Processing [v10]

[Erik Österlund]

On Tue, 6 Oct 2020 02:26:16 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Erik Österlund has updated the pull request with a new target base due to a merge or a rebase. The pull request now
>> contains 16 commits:
>>  - Review: Deal with new assert from mainline
>>  - Merge branch 'master' into 8253180_conc_stack_scanning
>>  - Review: StackWalker hook
>>  - Review: Kim CR 1 and exception handling fix
>>  - Review: Move barrier detach
>>  - Review: Remove assert that has outstayed its welcome
>>  - Merge branch 'master' into 8253180_conc_stack_scanning
>>  - Review: Albert CR2 and defensive programming
>>  - Review: StefanK CR 3
>>  - Review: Per CR 1
>>  - ... and 6 more: https://git.openjdk.java.net/jdk/compare/9604ee82...e633cb94
>
> src/hotspot/share/runtime/safepointMechanism.cpp line 89:
> 
>> 87:   //
>> 88:   // The call has been carefully placed here to cater for a few situations:
>> 89:   // 1) After we exit from block after a global pool
> 
> Typo: pool -> poll

Fixed.

> src/hotspot/share/runtime/stackWatermark.cpp line 223:
> 
>> 221: void StackWatermark::yield_processing() {
>> 222:   update_watermark();
>> 223:   MutexUnlocker mul(&_lock, Mutex::_no_safepoint_check_flag);
> 
> This seems a little dubious - is it just a heuristic? There is no guarantee that unlocking the Mutex will allow another
> thread to claim it before this thread re-locks it.

It is indeed just a heuristic. There is no need for a guarantee.

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PR: https://git.openjdk.java.net/jdk/pull/296