On Tue, 14 Nov 2023 21:54:06 GMT, Alex Menkov <amen...@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.
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
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);
}
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/16665#discussion_r1395079535
PR Review Comment: https://git.openjdk.org/jdk/pull/16665#discussion_r1395071539
PR Review Comment: https://git.openjdk.org/jdk/pull/16665#discussion_r1395084194
