RFR: JDK-8322237: Heap dump contains duplicate thread records for mounted virtual threads

[David Holmes]

On Sat, 16 Dec 2023 02:15:16 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

> HeapDumper dumps virtual threads in 2 places:
> - dumping platform threads (mounted virtual threads are dumped as separate thread object);
> - dumping heap objects when the object is `java.lang.VirtualThread`.
> 
> In the 2nd case mounted virtual threads should be skipped (as they are already dumped with correct stack traces/stack references)
> Check that a virtual thread is mounted is non-trivial, method from JvmtiEnvBase was used for this.
> 
> Testing: tier1..3, heapdump-related tests: open/test/hotspot/jtreg/serviceability,open/test/hotspot/jtreg/runtime/ErrorHandling,open/test/hotspot/jtreg/gc/epsilon,open/test/jdk/sun/tools/jhsdb

src/hotspot/share/services/heapDumper.cpp line 1647:

> 1645:   static bool is_vthread_mounted(oop vt) {
> 1646:     return JvmtiEnvBase::get_JavaThread_or_null(vt) != nullptr;
> 1647:   }

It doesn't seem appropriate to couple this to the JVMTI code (can this code be present if JVMTI is not part of the build?). Doesn't the VT state give you a good enough approximation of whether it is mounted i.e. RUNNABLE?

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PR Review Comment: https://git.openjdk.org/jdk/pull/17134#discussion_r1430801839