RFR: 8294075: gtest/AsyncLogGtest crashes with SEGV

[David Holmes]

On Wed, 21 Sep 2022 02:34:03 GMT, Xin Liu <xliu at openjdk.org> wrote:

> In order to test "drop messages scenario", I replace the serving buffers with shrunk buffers(1k).
> This is done by RAII class 'AsyncLogWriter::BufferUpdater'. There is a race condition between test and AsyncLog thread. 
> The race condition exhibits when AsyncLog thread is still processing `buffer_staging` but test thread deletes it in dtor of BufferUpdater. 
> 
> This patch issues AsyncLogWriter::flush() before dtor of BufferUpdater. buffers are reverted only when pending messages have all been handled.
> 
> I test TEST="jtreg:hotspot/jtreg/gtest/AsyncLogGtest.java" 100 times and never see race condition.

Based on the explanation of the bug this fix seems reasonable.

Thanks.

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Marked as reviewed by dholmes (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10367