On Thu, 30 Nov 2023 00:26:25 GMT, Alex Menkov <[email protected]> wrote:
>> The change impelements dumping of unmounted virtual threads data (stack
>> traces and stack references).
>> Unmounted vthreads can be detected only by iterating over the heap, but
>> hprof stack trace records (HPROF_FRAME/HPROF_TRACE) should be written before
>> HPROF_HEAP_DUMP/HPROF_HEAP_DUMP_SEGMENT.
>> HeapDumper supports segment dump (parallel dump to separate files with
>> subsequent file merge outside of safepoint), the fix switches HeapDumper to
>> always use segment dump: 1st segment contains only non-heap data, other
>> segments are used for dumping heap objects. For serial dumping
>> single-threaded dumping is performed, but 2 segments are created anyway.
>> When HeapObjectDumper detects unmounted virtual thread, it writes
>> HPROF_FRAME/HPROF_TRACE records to the 1st segment ("global writer"), and
>> writes thread object (HPROF_GC_ROOT_JAVA_FRAME) and stack references
>> (HPROF_GC_ROOT_JAVA_FRAME/HPROF_GC_ROOT_JNI_LOCAL) to the HeapObjectDumper
>> segment.
>> As parallel dumpers may write HPROF_FRAME/HPROF_TRACE concurrently and
>> VMDumper needs to write non-heap data before heap object dumpers can write
>> virtual threads data, writing to global writer is protected with
>> DumperController::_global_writer_lock.
>>
>> Testing: run tests which perform heap dump (in different scenarios):
>> - test/hotspot/jtreg/serviceability
>> - test/hotspot/jtreg/runtime/ErrorHandling
>> - test/hotspot/jtreg/gc/epsilon
>> - test/jdk/sun/tools/jhsdb
>
> Alex Menkov has updated the pull request incrementally with two additional
> commits since the last revision:
>
> - feedback
> - prepare_parallel_dum
Marked as reviewed by cjplummer (Reviewer).
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PR Review: https://git.openjdk.org/jdk/pull/16665#pullrequestreview-1771272003
