RFR: 8273614: Shenandoah: intermittent timeout with ConcurrentGCBreakpoint tests [v2]

[Aleksey Shipilev]

On Mon, 11 Oct 2021 12:42:33 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> I were able to reproduce with aggressive heuristics. 
>> 
>> A _wb_breakpoint GC request , while a concurrent GC is started. ShenandoahBreakpoint::_start_gc may not get set, as we bypass it if it is not a _wb_breakpoint GC, then we are forever blocked in ShenandoahBreakpoint::at_before_gc(), waiting for the flag to be set.
>> 
>> The solution is only run breakpoints during _wb_breakpoint GC.
>> 
>> Also, enforced _requested_gc_cause and _gc_requested order, ensure that read side sees latest _requested_gc_cause.
>> 
>> Test:
>> 
>> - [x] tier1 with Shenandoah
>
> Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Aleksey's comment

Marked as reviewed by shade (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/5868