src/share/vm/prims/jvmtiEnvBase.cpp

*** 995,1011 ****
        // This monitor is owned so we have to find the owning JavaThread.
        // Since owning_thread_from_monitor_owner() grabs a lock, GC can
        // move our object at this point. However, our owner value is safe
        // since it is either the Lock word on a stack or a JavaThread *.
        owning_thread = Threads::owning_thread_from_monitor_owner(owner, !at_safepoint);
!       assert(owning_thread != NULL, "sanity check");
!       if (owning_thread != NULL) {  // robustness
          // The monitor's owner either has to be the current thread, at safepoint
          // or it has to be suspended. Any of these conditions will prevent both
          // contending and waiting threads from modifying the state of
          // the monitor.
          if (!at_safepoint && !JvmtiEnv::is_thread_fully_suspended(owning_thread, true, &debug_bits)) {
            return JVMTI_ERROR_THREAD_NOT_SUSPENDED;
          }
          HandleMark hm;
          Handle     th(owning_thread->threadObj());
          ret.owner = (jthread)jni_reference(calling_thread, th);
--- 995,1017 ----
        // This monitor is owned so we have to find the owning JavaThread.
        // Since owning_thread_from_monitor_owner() grabs a lock, GC can
        // move our object at this point. However, our owner value is safe
        // since it is either the Lock word on a stack or a JavaThread *.
        owning_thread = Threads::owning_thread_from_monitor_owner(owner, !at_safepoint);
!       // Cannot assume (owning_thread != NULL) here because this function
!       // may not have been called at a safepoint and the owning_thread
!       // might not be suspended.
!       if (owning_thread != NULL) {
          // The monitor's owner either has to be the current thread, at safepoint
          // or it has to be suspended. Any of these conditions will prevent both
          // contending and waiting threads from modifying the state of
          // the monitor.
          if (!at_safepoint && !JvmtiEnv::is_thread_fully_suspended(owning_thread, true, &debug_bits)) {
+           // Don't worry! This return of JVMTI_ERROR_THREAD_NOT_SUSPENDED
+           // will not make it back to the JVM/TI agent. The error code will
+           // get intercepted in JvmtiEnv::GetObjectMonitorUsage() which
+           // will retry the call via a VM_GetObjectMonitorUsage VM op.
            return JVMTI_ERROR_THREAD_NOT_SUSPENDED;
          }
          HandleMark hm;
          Handle     th(owning_thread->threadObj());
          ret.owner = (jthread)jni_reference(calling_thread, th);