RFR: 8267666: Add option to jcmd GC.heap_dump to use existing file

[Lin Zang]

On Wed, 26 May 2021 09:34:06 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> Please review a small change that adds an option to GC.heap_dump to use an existing file. 
>> 
>> The option is necessary if the target file is a predefined file-like object, like a named pipe. This opens up a lot of possibilities to process a heap dump without storing it to the file system first.
>> 
>> Reviews of the CSR linked to the bug would be appreciated as well.
>
> AFAIK such enhancement was not discussed before. Please consider this review request also as a start of a discussion. The implementation is rather small, so I thought it was not worth a separate CFD in advance.
> 
> I added few details to the bug. The change does not depend on a particular operating system, but on Linux, for example, the new option allows sending the dump to the external LZ4 process. It provides a compressed dump of the heap 2x faster than it is possible now, at the speed comparable to writing uncompressed dump.
> 
> Thanks!

Hi @AntonKozlov, 
I am not a reviewer, just a tiny hint that you may need to add test cases. 
Thanks,
Lin

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PR: https://git.openjdk.java.net/jdk/pull/4183