RFR: 8268857: Merge three vm operations in thread_dump

[Denghui Dong]

On Wed, 16 Jun 2021 04:08:10 GMT, David Holmes <dholmes at openjdk.org> wrote:

> Sorry but I do not agree with this change. I understand your rationale but you have overlooked that by combining these three safepoint operations you have created a much longer safepoint pause which may lock out other more important safepoint operations, and you may also be holding the HeapLock across this extended safepoint.
> 
> The operations that you have coalesced are not considered time critical but can themselves be very time consuming e.g deadlock detection.
> 
> David

Hi David,

Thanks for the comment.

I still think it's redundant to enter three safepoint, which may lead to inconsistent results between 'PrintThreads' and 'FindDeadlocks'. But this patch does cause the problem you said

I will reopen it once I have a better solution.

Thanks,
Denghui

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PR: https://git.openjdk.java.net/jdk/pull/4504