On Sun, 19 Nov 2023 03:47:45 GMT, Daniel D. Daugherty <dcu...@openjdk.org> wrote:
>> Thank you for the comment, Dan! >> Agreed, the comment needs to be corrected in two aspects. >> I tried to simplify it but failed to do it correctly. >> It is interesting that there is a `ThreadsListHandle` farther up the stack >> but it does not help sometimes. >> It is observed that a `JavaThread` (of a carrier thread) referenced from the >> `JvmtiThreadState` object can be just created, so we need a >> `ThreadsListHandle` to avoid possible asserts. With this fix in place I do >> not see the asserts fired anymore. > > @sspitsyn - Please point me at the code where these JavaThreads are newly > created? @dcubed-ojdk I don't know FJP implementation well enough to point at the code where it happens. However, I observe that new `JavaThread `is being created between two points of the execution path. - First point is in the `JvmtiEventControllerPrivate::recompute_enabled()` at the line where a `ThreadsListHandle` is set. I've added a trap checking if any `JavaThread` pointed by `state->get_thread()` is not protected by the `tlh`. I can see this trap is not fired (I can't say it has never been fired). - Second point is in the `JvmtiEventControllerPrivate::enter_interp_only_mode()`. If a `ThreadsListHandle` is NOT set then I can observe a `JavaThread` referenced by the state->get_thread() which is not protected by any TLH. It a TLH added into `JvmtiEventControllerPrivate::enter_interp_only_mode()` then this `JavaThread` is observed as protected by TLH. I can provide a full stack trace for this `JavaThread` consisting of two parts: carrier thread and virtual thread frames. The name of carrier thread is `ForkJoinPool-1-worker-1`. The virtual thread is a tested virtual thread. The thread dump looks las below: DBG: enter_interp_only_mode: target: 0x7f93f8043d00 <NO-NAME> virt: 1 carrier: ForkJoinPool-1-worker-1 DBG: ##### NATIVE stacktrace of JavaThread: 0x7f93f8043d00 ##### Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code) j fieldacc02.check(Ljava/lang/Object;)I+0 j fieldacc02.lambda$testVirtualThread$0()V+12 j fieldacc02$$Lambda+0x00007f943b001428.run()V+0 j java.lang.Thread.runWith(Ljava/lang/Object;Ljava/lang/Runnable;)V+5 java.base@22-internal j java.lang.VirtualThread.run(Ljava/lang/Runnable;)V+66 java.base@22-internal j java.lang.VirtualThread$VThreadContinuation$1.run()V+8 java.base@22-internal j jdk.internal.vm.Continuation.enter0()V+4 java.base@22-internal j jdk.internal.vm.Continuation.enter(Ljdk/internal/vm/Continuation;Z)V+1 java.base@22-internal J 124 jdk.internal.vm.Continuation.enterSpecial(Ljdk/internal/vm/Continuation;ZZ)V java.base@22-internal (0 bytes) @ 0x00007f94c7cdf744 [0x00007f94c7cdf5e0+0x0000000000000164] j jdk.internal.vm.Continuation.run()V+122 java.base@22-internal j java.lang.VirtualThread.runContinuation()V+70 java.base@22-internal j java.lang.VirtualThread$$Lambda+0x00007f943b0496c0.run()V+4 java.base@22-internal j java.util.concurrent.ForkJoinTask$RunnableExecuteAction.compute()Ljava/lang/Void;+4 java.base@22-internal j java.util.concurrent.ForkJoinTask$RunnableExecuteAction.compute()Ljava/lang/Object;+1 java.base@22-internal j java.util.concurrent.ForkJoinTask$InterruptibleTask.exec()Z+51 java.base@22-internal j java.util.concurrent.ForkJoinTask.doExec()V+10 java.base@22-internal j java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(Ljava/util/concurrent/ForkJoinTask;Ljava/util/concurrent/ForkJoinPool$WorkQueue;I)V+49 java.base@22-internal j java.util.concurrent.ForkJoinPool.scan(Ljava/util/concurrent/ForkJoinPool$WorkQueue;JI)J+271 java.base@22-internal j java.util.concurrent.ForkJoinPool.runWorker(Ljava/util/concurrent/ForkJoinPool$WorkQueue;)V+68 java.base@22-internal j java.util.concurrent.ForkJoinWorkerThread.run()V+31 java.base@22-internal v ~StubRoutines::call_stub 0x00007f94c7505d21 V [libjvm.so+0xe7b719] JavaCalls::call_helper(JavaValue*, methodHandle const&, JavaCallArguments*, JavaThread*)+0x4a9 (javaCalls.cpp:415) V [libjvm.so+0xe7bdd5] JavaCalls::call_virtual(JavaValue*, Klass*, Symbol*, Symbol*, JavaCallArguments*, JavaThread*)+0x345 (javaCalls.cpp:329) V [libjvm.so+0xe7bff6] JavaCalls::call_virtual(JavaValue*, Handle, Klass*, Symbol*, Symbol*, JavaThread*)+0x76 (javaCalls.cpp:191) V [libjvm.so+0xfd9723] thread_entry(JavaThread*, JavaThread*)+0x93 (jvm.cpp:2937) V [libjvm.so+0xeb06ac] JavaThread::thread_main_inner()+0xcc (javaThread.cpp:720) V [libjvm.so+0x1789496] Thread::call_run()+0xb6 (thread.cpp:220) V [libjvm.so+0x1493b27] thread_native_entry(Thread*)+0x127 (os_linux.cpp:787) The observed `JavaThead` does not look as a garbage because no crashes has ever been observed. Apparently, it has been recently created because it is not protected by the TLH which was set in the `JvmtiEventControllerPrivate::recompute_enabled()`. I guess, it has to be possible to find out where exactly in the FJP code it is created but it will take time. I'm not sure why do you need it though. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/16686#discussion_r1398362375
