src/share/vm/runtime/objectMonitor.cpp

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*** 1,7 **** /* ! * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. --- 1,7 ---- /* ! * Copyright (c) 1998, 2014, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.
*** 380,389 **** --- 380,395 ---- JavaThreadBlockedOnMonitorEnterState jtbmes(jt, this); DTRACE_MONITOR_PROBE(contended__enter, this, object(), jt); if (JvmtiExport::should_post_monitor_contended_enter()) { JvmtiExport::post_monitor_contended_enter(jt, this); + + // The current thread does not yet own the monitor and does not + // yet appear on any queues that would get it made the successor. + // This means that the JVMTI_EVENT_MONITOR_CONTENDED_ENTER event + // handler cannot accidentally consume an unpark() meant for the + // ParkEvent associated with this ObjectMonitor. } OSThreadContendState osts(Self->osthread()); ThreadBlockInVM tbivm(jt);
*** 437,446 **** --- 443,458 ---- // spinning we could increment JVMStat counters, etc. DTRACE_MONITOR_PROBE(contended__entered, this, object(), jt); if (JvmtiExport::should_post_monitor_contended_entered()) { JvmtiExport::post_monitor_contended_entered(jt, this); + + // The current thread already owns the monitor and is not going to + // call park() for the remainder of the monitor enter protocol. So + // it doesn't matter if the JVMTI_EVENT_MONITOR_CONTENDED_ENTERED + // event handler consumed an unpark() issued by the thread that + // just exited the monitor. } if (event.should_commit()) { event.set_klass(((oop)this->object())->klass()); event.set_previousOwner((TYPE_JAVALANGTHREAD)_previous_owner_tid);
*** 1454,1463 **** --- 1466,1483 ---- // post monitor waited event. Note that this is past-tense, we are done waiting. if (JvmtiExport::should_post_monitor_waited()) { // Note: 'false' parameter is passed here because the // wait was not timed out due to thread interrupt. JvmtiExport::post_monitor_waited(jt, this, false); + + // In this short circuit of the monitor wait protocol, the + // current thread never drops ownership of the monitor and + // never gets added to the wait queue so the current thread + // cannot be made the successor. This means that the + // JVMTI_EVENT_MONITOR_WAITED event handler cannot accidentally + // consume an unpark() meant for the ParkEvent associated with + // this ObjectMonitor. } if (event.should_commit()) { post_monitor_wait_event(&event, 0, millis, false); } TEVENT (Wait - Throw IEX) ;
*** 1497,1521 **** _waiters++; // increment the number of waiters _recursions = 0; // set the recursion level to be 1 exit (true, Self) ; // exit the monitor guarantee (_owner != Self, "invariant") ; - // As soon as the ObjectMonitor's ownership is dropped in the exit() - // call above, another thread can enter() the ObjectMonitor, do the - // notify(), and exit() the ObjectMonitor. If the other thread's - // exit() call chooses this thread as the successor and the unpark() - // call happens to occur while this thread is posting a - // MONITOR_CONTENDED_EXIT event, then we run the risk of the event - // handler using RawMonitors and consuming the unpark(). - // - // To avoid the problem, we re-post the event. This does no harm - // even if the original unpark() was not consumed because we are the - // chosen successor for this monitor. - if (node._notified != 0 && _succ == Self) { - node._event->unpark(); - } - // The thread is on the WaitSet list - now park() it. // On MP systems it's conceivable that a brief spin before we park // could be profitable. // // TODO-FIXME: change the following logic to a loop of the form --- 1517,1526 ----
*** 1595,1604 **** --- 1600,1636 ---- // post monitor waited event. Note that this is past-tense, we are done waiting. if (JvmtiExport::should_post_monitor_waited()) { JvmtiExport::post_monitor_waited(jt, this, ret == OS_TIMEOUT); } + // Without the fix for 8028280, it is possible for the above call: + // + // Thread::SpinAcquire (&_WaitSetLock, "WaitSet - unlink") ; + // + // to consume the unpark() that was done when the successor was set. + // The solution for this very rare possibility is to redo the unpark() + // outside of the JvmtiExport::should_post_monitor_waited() check. + // + if (node._notified != 0 && _succ == Self) { + // In this part of the monitor wait-notify-reenter protocol it + // is possible (and normal) for another thread to do a fastpath + // monitor enter-exit while this thread is still trying to get + // to the reenter portion of the protocol. + // + // The ObjectMonitor was notified and the current thread is + // the successor which also means that an unpark() has already + // been done. The JVMTI_EVENT_MONITOR_WAITED event handler can + // consume the unpark() that was done when the successor was + // set because the same ParkEvent is shared between Java + // monitors and JVM/TI RawMonitors (for now). + // + // We redo the unpark() to ensure forward progress, i.e., we + // don't want all pending threads hanging (parked) with none + // entering the unlocked monitor. + node._event->unpark(); + } + if (event.should_commit()) { post_monitor_wait_event(&event, node._notifier_tid, millis, ret == OS_TIMEOUT); } OrderAccess::fence() ;