RFR: 8268857: Merge three vm operations in thread_dump

[Thomas Stuefe]

On Wed, 16 Jun 2021 03:33:14 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.

It would be nice to have this fixed though. Maybe adding a guaranteed timeout to these operations would help.

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