RFR: 8268857: Merge three vm operations in thread_dump [v3]

[David Holmes]

On Thu, 17 Jun 2021 15:32:01 GMT, Denghui Dong <ddong at openjdk.org> wrote:

>> Hi,
>> 
>> Could I have a review of this change that merges three vm operations(VM_PrintThreads, VM_PrintJNI, VM_FindDeadlocks) in thread_dump and signal_thread_entry.
>> 
>> `jstack` is a very common command, even in the production environment.
>> 
>> In addition to reduce the cost of entering safepoint, I think this patch also could ensure the consistency of the results of VM_PrintThreads and VM_FindDeadlocks.
>
> Denghui Dong has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - add cutoff support for find_deadlocks_at_safepoint
>  - remove useless field '_is_deadlock'

Sorry still not a fan even with the hacked in deadline support for find_deadlocks. It is too arbitrary - you have no idea what constitutes a reasonable deadline, nor by how much you may overshoot that deadline.

David

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