[crac] RFR: Report checkpoint processing to jcmd [v21]

[Ilarion Nakonechnyy]

On Thu, 11 Aug 2022 15:06:25 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> Ilarion Nakonechnyy has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - implement checkpointRestoreLocked
>>  - Revert "java core crac corections"
>>    
>>    This reverts commit 6a2b03b77f1ee4e6d48a120a14694d8dff9dbf39.
>
> src/hotspot/os/linux/attachListener_linux.cpp line 359:
> 
>> 357: 
>> 358:   if (_effectively_completed) {
>> 359:     return;
> 
> An assert here would catch lost output that won't be reported anywhere.
> Suggestion:
> 
>     assert(st->size() == 0, "no lost output");
>     return;

A straightforward implementation of this assertion leads to triggering it at restore. 
Seems like `LinuxAttachListener::write_fully()` doesnt reset the buffer_pos in `bufferedStream`, so the `bufferedStream->size() `is non-zero.  

Probably, it worth to add `bufferedStream->reset()` to `LinuxAttachOperation::write_operation_result()`

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PR: https://git.openjdk.org/crac/pull/10