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.
-------------
Commit messages:
- vthreads in heapdump
Changes: https://git.openjdk.org/jdk/pull/16665/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16665&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8299426
Stats: 308 lines in 3 files changed: 145 ins; 76 del; 87 mod
Patch: https://git.openjdk.org/jdk/pull/16665.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/16665/head:pull/16665
PR: https://git.openjdk.org/jdk/pull/16665
