On Sun, 19 Nov 2023 09:41:34 GMT, Serguei Spitsyn <sspit...@openjdk.org> wrote:
>> @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 <unnamed> 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$RunnableExecuteAction.compute()Ljava/lang/Void;+4 >> java.base@22-internal >> j java.util.concur... > > The stack trace of current thread (where the assert was fired) can explain > what is going on a little bit: > > Current thread (0x00007f93f8043d00): JavaThread "ForkJoinPool-1-worker-1" > daemon [_thread_in_vm, id=16779, stack(0x00007f948a597000,0x00007f948a697000) > (1024K)] > > Stack: [0x00007f948a597000,0x00007f948a697000], sp=0x00007f948a6949e0, free > space=1014k > Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native > code) > V [libjvm.so+0x117937d] > JvmtiEventControllerPrivate::enter_interp_only_mode(JvmtiThreadState*)+0x45d > (jvmtiEventController.cpp:402) > V [libjvm.so+0x1179520] > JvmtiEventControllerPrivate::recompute_thread_enabled(JvmtiThreadState*) > [clone .part.0]+0x190 (jvmtiEventController.cpp:632) > V [libjvm.so+0x117a1e1] > JvmtiEventControllerPrivate::thread_started(JavaThread*)+0x351 > (jvmtiEventController.cpp:1174) > V [libjvm.so+0x117e608] > JvmtiExport::get_jvmti_thread_state(JavaThread*)+0x98 (jvmtiExport.cpp:424) > V [libjvm.so+0x118a86c] JvmtiExport::post_field_access(JavaThread*, > Method*, unsigned char*, Klass*, Handle, _jfieldID*)+0x6c > (jvmtiExport.cpp:2214) > V [libjvm.so+0x118b3a1] JvmtiExport::post_field_access_by_jni(JavaThread*, > oop, Klass*, _jfieldID*, bool)+0x321 (jvmtiExport.cpp:2202) > V [libjvm.so+0x118b4e9] JvmtiExport::jni_GetField_probe(JavaThread*, > _jobject*, oop, Klass*, _jfieldID*, bool)+0x79 (jvmtiExport.cpp:2168) > V [libjvm.so+0xf83847] jni_GetStaticBooleanField+0x257 (jni.cpp:2047) > C [libfieldacc02.so+0x379b] Java_fieldacc02_check+0x6b (jni.h:1546) > j fieldacc02.check(Ljava/lang/Object;)I+0 > j fieldacc02.lambda$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.concur... Just to re-iterate what Dan was saying, the TLH is only of use if you are accessing threads known to be included in the TLH. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/16686#discussion_r1398540533
