RFR: 8257234 : Add gz option to SA jmap to write a gzipped heap dump [v14]

[Serguei Spitsyn]

On Fri, 5 Feb 2021 15:32:26 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> One implementation is in the JVM itself, to be used when the JVM is still running well, and not just from command line tools. Heap dumping can also be triggered by the JVM itslef by setting flags like -XX:+HeapDumpBeforeFullGC. The other implementation is in SA, to be used on a core file or a hung JVM process, although it can also be used on a JVM that is still running well. BTW, there used to be a 3rd implementation. The old hprof profiler (a JVMTI agent) also was used to generate hprof files.
>
> Dear @plummercj,
> 
>> `--dumpfile` and `--gz` can only be used with `--binaryheap`. That should be made clear in the help text.
> 
> I added indentation for these two sub-options.
> 
>> * SA's `jhsdb jmap --binaryheap` (which uses JMap.java with `-heap:format=b`)
>> * SA's clhsdb `dumpheap` command (which also uses JMap.java with `-heap:format=b`)
>> * executing  SA's `sun/jvm/hotspot/tools/JMap` class directly
>> * `jmap -dump` command (Uses Attach API's `heapdump` command, which uses hotspot `HeapDump` class)
>> * `GC.heap_dump` dcmd, which also uses the hotspot `HeapDumper` class
> All 5 commands help message have been tested.

Hi Lin,
Thank you for the update with requested changes.
Please, note, my suggestion was rough and still needs to be tested/checked for potential bugs. :)
I'll look at changes in other files as well.
Thanks,
Serguei

-------------

PR: https://git.openjdk.java.net/jdk/pull/1712