RFR: JDK-8327769: jcmd GC.heap_dump without options should write to location given by -XX:HeapDumpPath, if set [v10]

[Chris Plummer]

On Wed, 27 Mar 2024 13:44:42 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

>> Currently jcmd command GC.heap_dump only works with an additionally provided file name.
>> Syntax : GC.heap_dump [options] <filename>
>> 
>> In case the JVM has the XX - flag HeapDumpPath set, we should support an additional mode where the <filename> is optional.
>> In case the filename is NOT set, we take the HeapDumpPath (file or directory);
>> 
>> new syntax :
>> GC.heap_dump [options] <filename> .. has precedence over second option
>> GC.heap_dump [options] …in case -XX: HeapDumpPath=p is set
>> 
>> This would be a simplification e.g. for support cases where a filename or directory is set at JVM startup with -XX: HeapDumpPath=p and writing to the path is intended/recommended for usage also in the jcmd case.
>
> Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:
> 
>   adjust java.1 man page

One other thing I just realized is that if we go through with this change, then we can't in the future change VM.heap_dump so it can be used without any filename (make it use a default filename when no filename is specified). Setting HeapDumpPath would override this default filename, and it would be really confusing to the user when suddenly heap dumps are not appearing in the default location with the default name because someone decided to specify HeapDumpPath when launching the JVM.

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PR Comment: https://git.openjdk.org/jdk/pull/18190#issuecomment-2046523158