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8180599: Possibly miss to iterate monitors on thread exit

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Move thread-local monitors to global lists before thread is removed from global threads list, to ensure all monitors get scanned

Reviewed-by: dholmes, rehn
This commit is contained in:
Roman Kennke 2017-05-19 12:14:38 +02:00
parent 4e05c8c099
commit 8bda8fc602
2 changed files with 13 additions and 10 deletions
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16
hotspot/src/share/vm/runtime/synchronizer.cpp
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@ -1283,14 +1283,14 @@ void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
// a global gOmInUseList under the global list lock so these
// will continue to be scanned.
//
// We currently call omFlush() from the Thread:: dtor _after the thread
// We currently call omFlush() from Threads::remove() _before the thread
// has been excised from the thread list and is no longer a mutator.
// That means that omFlush() can run concurrently with a safepoint and
// the scavenge operator. Calling omFlush() from JavaThread::exit() might
// be a better choice as we could safely reason that that the JVM is
// not at a safepoint at the time of the call, and thus there could
// be not inopportune interleavings between omFlush() and the scavenge
// operator.
// This means that omFlush() can not run concurrently with a safepoint and
// interleave with the scavenge operator. In particular, this ensures that
// the thread's monitors are scanned by a GC safepoint, either via
// Thread::oops_do() (if safepoint happens before omFlush()) or via
// ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
// monitors have been transferred to the global in-use list).
void ObjectSynchronizer::omFlush(Thread * Self) {
ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
@ -1338,6 +1338,8 @@ void ObjectSynchronizer::omFlush(Thread * Self) {
tail->FreeNext = gFreeList;
gFreeList = list;
gMonitorFreeCount += tally;
assert(Self->omFreeCount == tally, "free-count off");
Self->omFreeCount = 0;
}
if (inUseTail != NULL) {

7
hotspot/src/share/vm/runtime/thread.cpp
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@ -336,9 +336,6 @@ void Thread::record_stack_base_and_size() {
Thread::~Thread() {
// Reclaim the objectmonitors from the omFreeList of the moribund thread.
ObjectSynchronizer::omFlush(this);
EVENT_THREAD_DESTRUCT(this);
// stack_base can be NULL if the thread is never started or exited before
@ -4251,6 +4248,10 @@ void Threads::add(JavaThread* p, bool force_daemon) {
}
void Threads::remove(JavaThread* p) {
// Reclaim the objectmonitors from the omInUseList and omFreeList of the moribund thread.
ObjectSynchronizer::omFlush(p);
// Extra scope needed for Thread_lock, so we can check
// that we do not remove thread without safepoint code notice
{ MutexLocker ml(Threads_lock);