RFR: 8370203 - Add jcmd AOT.end_recording diagnostic command [v7]

[Kevin Walls]

On Tue, 25 Nov 2025 01:01:19 GMT, Mat Carter <macarte at openjdk.org> wrote:

>> Add jcmd AOT.end_recording diagnostic command.  When this command is issued, a targeted JVM that is currently recording AOT information will stop recording.  Existing functionality is preserved: when stopped the JVM will create the required artifacts based on the execution mode.  Conveniently as the application running on the JVM has not stopped (as was previously the only way to stop recording), the application will resume execution after the artifacts have been generated.
>> 
>> The command will report back to the user one of the following messages depending on the state of the JVM:
>> 
>> - AOT.end_recording is unsupported when VM flags -XX:AOTMode=record or -XX:AOTCacheOutput=<file> are missing
>> - Recording has already ended.
>> - Error: Failed to end recording.
>> - Recording ended successfully.
>> 
>> It follows that issues the command to a JVM that is recording, twice in succession, should (baring internal errors) would produce the following two responses:
>> 
>> - Recording ended successfully.
>> - Recording has already ended.
>> 
>> Passes tier1 on linux (x64) and windows (x64)
>
> Mat Carter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Check exit value in tests

Looking good I think.

A possible general issue is that the AOT implementation of the dumping may write mesages on tty-> but they are not captured by the jcmd.  Not too much of an issue for a training run as presumably the app is being monitored by whoever asks for the endRecording() to happen.  I think the plan for now would be: should the jcmd fail, you check the app output for possibly more detail.

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PR Comment: https://git.openjdk.org/jdk/pull/27965#issuecomment-3575650962