Thread-local mark stacks for the CC collector.
Thread-local mark stacks are assigned to mutators where they push
references in read barriers to reduce the (CAS) synchronization cost
in a global mark stack/queue.
We step through three mark stack modes (thread-local, shared,
GC-exclusive) and use per-thread flags to disable/enable system weak
accesses (only for the CC collector) instead of the existing global
one to safely perform the marking phase. The reasons are 1)
thread-local mark stacks for mutators need to be revoked using a
checkpoint to avoid races (incorrectly leaving a reference on mark
stacks) when terminating marking, and 2) we can’t use a checkpoint
while system weak accesses are disabled (or a deadlock would
happen). More details are described in the code comments.
Performance improvements in Ritzperf EAAC: a ~2.8% improvement
(13290->12918) in run time and a ~23% improvement (51.6s->39.8s) in
the total GC time on N5.
Bug: 12687968
Change-Id: I5d234d7e48bf115cd773d38bdb62ad24ce9116c7
diff --git a/runtime/monitor.cc b/runtime/monitor.cc
index 4be25d6..bc89890 100644
--- a/runtime/monitor.cc
+++ b/runtime/monitor.cc
@@ -1146,10 +1146,18 @@
CHECK(!allow_new_monitors_);
}
+void MonitorList::BroadcastForNewMonitors() {
+ CHECK(kUseReadBarrier);
+ Thread* self = Thread::Current();
+ MutexLock mu(self, monitor_list_lock_);
+ monitor_add_condition_.Broadcast(self);
+}
+
void MonitorList::Add(Monitor* m) {
Thread* self = Thread::Current();
MutexLock mu(self, monitor_list_lock_);
- while (UNLIKELY(!allow_new_monitors_)) {
+ while (UNLIKELY((!kUseReadBarrier && !allow_new_monitors_) ||
+ (kUseReadBarrier && !self->GetWeakRefAccessEnabled()))) {
monitor_add_condition_.WaitHoldingLocks(self);
}
list_.push_front(m);