On Thu, 16 Nov 2023 02:30:23 GMT, Yi Yang <yy...@openjdk.org> 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
>
> src/hotspot/share/services/heapDumper.cpp line 1896:
>
>> 1894:
>> 1895: public:
>> 1896: HeapObjectDumper(AbstractDumpWriter* writer, UnmountedVThreadDumper*
>> vthread_dumper)
>
> Maybe we can pass global writer to HeapObjectDumper and thus simplify the
> implementation? We can remove `class VM_HeapDumper : public VM_GC_Operation,
> public WorkerTask, public UnmountedVThreadDumper {` and
> `UnmountedVThreadDumper` then.
This was an initial plan, but it would require more refactoring (dumper for
unmounted vthreads needs a way to lock global writer, so need to move
DumperController declaration and definition or add new 'class GlobalDumpWriter:
public DumpWriter' and implement the lock there). I prefer to make functional
changes here with minimum refactoring to simplify review and do refactoring in
follow-up fixes
> src/hotspot/share/services/heapDumper.cpp line 2024:
>
>> 2022: char* DumpMerger::get_writer_path(const char* base_path, int seq) {
>> 2023: // calculate required buffer size
>> 2024: size_t buf_size = strlen(base_path)
>
> Format
fixed
> src/hotspot/share/services/heapDumper.cpp line 2411:
>
>> 2409:
>> 2410: WorkerThreads* workers = ch->safepoint_workers();
>> 2411: update_parallel_dump_count(workers);
>
> Maybe consolidate them together
>
> update_parallel_dump_count(workers);
>
>
> =>
>
> prepare_parallel_dump(workers){
> ... // copy from update_parallel_dump_count
> _dumper_controller = new (std::nothrow)
> DumperController(_num_dumper_threads);
> }
Done
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/16665#discussion_r1396386291
PR Review Comment: https://git.openjdk.org/jdk/pull/16665#discussion_r1396359118
PR Review Comment: https://git.openjdk.org/jdk/pull/16665#discussion_r1396359593
