RFR: 8308500: ZStatSubPhase::register_start should not call register_gc_phase_start if ZAbort::should_abort()

[Stefan Karlsson]

On Mon, 22 May 2023 07:37:19 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> `ZStatSubPhase::register_start` should not call `register_gc_phase_start` if `ZAbort::should_abort()` is true. This will cause an unbalanced push and pop behaviour of the phase stack as `ZStatSubPhase::register_end` stops popping (and sending events) after the aborting has started. This will create an issue if more subsequent sub-phases are added in-between two abort points as the phase stack may overflow. 
> 
> Simply avoid pushing new phases when aborting has started solves this issue.

Changes requested by stefank (Reviewer).

src/hotspot/share/gc/z/zStat.cpp line 811:

> 809: 
> 810: void ZStatSubPhase::register_start(ConcurrentGCTimer* timer, const Ticks& start) const {
> 811:   if (timer != nullptr && !ZAbort::should_abort()) {

`register_end` also skips the logging part if we should abort. Should we do the same for the `register_start`?

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PR Review: https://git.openjdk.org/jdk/pull/14075#pullrequestreview-1436354071
PR Review Comment: https://git.openjdk.org/jdk/pull/14075#discussion_r1200344003