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/java_vm_ext.cc b/runtime/java_vm_ext.cc
index f1deacf..36adbea 100644
--- a/runtime/java_vm_ext.cc
+++ b/runtime/java_vm_ext.cc
@@ -473,7 +473,8 @@
return nullptr;
}
MutexLock mu(self, weak_globals_lock_);
- while (UNLIKELY(!allow_new_weak_globals_)) {
+ while (UNLIKELY((!kUseReadBarrier && !allow_new_weak_globals_) ||
+ (kUseReadBarrier && !self->GetWeakRefAccessEnabled()))) {
weak_globals_add_condition_.WaitHoldingLocks(self);
}
IndirectRef ref = weak_globals_.Add(IRT_FIRST_SEGMENT, obj);
@@ -559,6 +560,13 @@
CHECK(!allow_new_weak_globals_);
}
+void JavaVMExt::BroadcastForNewWeakGlobals() {
+ CHECK(kUseReadBarrier);
+ Thread* self = Thread::Current();
+ MutexLock mu(self, weak_globals_lock_);
+ weak_globals_add_condition_.Broadcast(self);
+}
+
mirror::Object* JavaVMExt::DecodeGlobal(Thread* self, IndirectRef ref) {
return globals_.SynchronizedGet(self, &globals_lock_, ref);
}
@@ -570,7 +578,8 @@
mirror::Object* JavaVMExt::DecodeWeakGlobal(Thread* self, IndirectRef ref) {
MutexLock mu(self, weak_globals_lock_);
- while (UNLIKELY(!allow_new_weak_globals_)) {
+ while (UNLIKELY((!kUseReadBarrier && !allow_new_weak_globals_) ||
+ (kUseReadBarrier && !self->GetWeakRefAccessEnabled()))) {
weak_globals_add_condition_.WaitHoldingLocks(self);
}
return weak_globals_.Get(ref);