On Wed, 7 Apr 2021 13:08:47 GMT, Richard Reingruber <rr...@openjdk.org> wrote:
>> Today the ThreadBlockInVM tbivm(current); is inside scope of >> JavaThreadBlockedOnMonitorEnterState jtbmes(current, this);. >> So this can happen today also. >> >> If you are context switch just before >> current->set_current_pending_monitor(NULL);. >> Someone suspends you and look at those states. >> >> If you agree that the issue is preexisting I prefer handling that outside >> scope of this. > >> Today the ThreadBlockInVM tbivm(current); is inside scope of >> JavaThreadBlockedOnMonitorEnterState jtbmes(current, this);. >> So this can happen today also. >> >> If you are context switch just before >> current->set_current_pending_monitor(NULL);. >> Someone suspends you and look at those states. >> > > You mean the JVMTI agent suspends the current thread and then observes that > the > thread state first has the attribute > JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER and > in a later call it does not have it anymore (~ThreadBlockInVM doesn't check > for > suspend)? Yes that's problematic too. > > With the new code we could remain suspended with > JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER. I think the OM would not be > reported as owned monitor but another thread could not lock it. > >> If you agree that the issue is preexisting I prefer handling that outside >> scope of this. > > I'm ok with that. > > A simple solution could then be making use of ThreadBlockInVM. When returning > from EnterI in L413 we would set a rollback function in the HandshakeState > which > can be called in HandshakeState::suspend_in_handshake() to exit the OM. I'm mean the state you describe will be seen on that line: - The current thread is set as owner in ObjectMonitor::_owner - The thread state will still be JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER because of the JavaThreadBlockedOnMonitorEnterState in L389. - Thread::_current_pending_monitor has not been reset to NULL. Will be seen while we are context while in blocked state before clearing the _current_pending_monitor. Ok good. ------------- PR: https://git.openjdk.java.net/jdk/pull/3191
