RFR: 8357650: ThreadSnapshot to take snapshot of thread for thread dumps [v4]

[Serguei Spitsyn]

On Thu, 29 May 2025 03:26:49 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

>> This is first (hotspot) part of the update for `HotSpotDiagnosticMXBean.dumpThreads` and `jcmd Thread.dump_to_file` to include lock information in thread dumps (JDK-8356870).
>> The update has been split into parts to simplify reviewing.
>> The fix contains an implementation of `jdk.internal.vm.ThreadSnapshot` class to gather required information about a thread.
>> Second (dependent) part includes changes in `HotSpotDiagnosticMXBean.dumpThreads`/`jcmd Thread.dump_to_file`, spec updates and tests for the functionality.
>> 
>> Testing: new `HotSpotDiagnosticMXBean.dumpThreads`/`jcmd Thread.dump_to_file` functionality was tested in loom repo;
>>   sanity tier1 (this fix only)
>
> Alex Menkov has updated the pull request incrementally with five additional commits since the last revision:
> 
>  - removed retry_handshake logic
>  - removed AbstractOwnableSynchronizer.exclusiveOwnerThread support
>  - cleanup
>  - renamed java_thread, thread_h
>  - fixed minimal and zero

src/hotspot/share/services/threadService.cpp line 1143:

> 1141:     };
> 1142: 
> 1143:     int _depth;

Nit: I'm thinking if `_depth` can be renamed to `_frame_depth`.
Then it will be self-explained, so no comment is needed.

src/hotspot/share/services/threadService.cpp line 1178:

> 1176:   GrowableArray<int>* _bcis;
> 1177:   JavaThreadStatus _thread_status;
> 1178:   OopHandle _name;

Nit: Maybe rename is to `_thread_name` or `_tname`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25425#discussion_r2113427639
PR Review Comment: https://git.openjdk.org/jdk/pull/25425#discussion_r2113430612