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6876794: 4/4 sp07t002 hangs very intermittently

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Remove over locking by VMThread on "is thread suspended?" check

Reviewed-by: dholmes, acorn, andrew
This commit is contained in:
Daniel D. Daugherty 2009-09-22 21:12:37 -06:00
parent 4e453ff713
commit f6523d1043
3 changed files with 18 additions and 13 deletions
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20
hotspot/src/share/vm/runtime/safepoint.cpp
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@ -769,9 +769,23 @@ void ThreadSafepointState::examine_state_of_thread() {
// to grab the Threads_lock which we own here, so a thread cannot be
// resumed during safepoint synchronization.
// We check with locking because another thread that has not yet
// synchronized may be trying to suspend this one.
bool is_suspended = _thread->is_any_suspended_with_lock();
// We check to see if this thread is suspended without locking to
// avoid deadlocking with a third thread that is waiting for this
// thread to be suspended. The third thread can notice the safepoint
// that we're trying to start at the beginning of its SR_lock->wait()
// call. If that happens, then the third thread will block on the
// safepoint while still holding the underlying SR_lock. We won't be
// able to get the SR_lock and we'll deadlock.
//
// We don't need to grab the SR_lock here for two reasons:
// 1) The suspend flags are both volatile and are set with an
// Atomic::cmpxchg() call so we should see the suspended
// state right away.
// 2) We're being called from the safepoint polling loop; if
// we don't see the suspended state on this iteration, then
// we'll come around again.
//
bool is_suspended = _thread->is_ext_suspended();
if (is_suspended) {
roll_forward(_at_safepoint);
return;