Remove a lock from ScopedThreadStateChange.
Remove a lock used while inspecting the current thread state in
ScopedThreadStateChange. It is safe to do so as the code just checks the
state and the suspend count checks occur in the transition logic (with
the appropriate locks held).
Gives small but noticeable performance improvement to the JniField
microbenchmark.
Change-Id: Iadda8ae0b30355dc3d7e4daeed760c41b3fecfc2
diff --git a/src/scoped_thread_state_change.h b/src/scoped_thread_state_change.h
index ed3c384..68fbf69 100644
--- a/src/scoped_thread_state_change.h
+++ b/src/scoped_thread_state_change.h
@@ -37,13 +37,14 @@
CHECK(!Runtime::Current()->IsStarted() || Runtime::Current()->IsShuttingDown());
} else {
bool runnable_transition;
- {
- MutexLock mu(*Locks::thread_suspend_count_lock_);
- old_thread_state_ = self->GetState();
- runnable_transition = old_thread_state_ == kRunnable || new_thread_state == kRunnable;
- if (!runnable_transition) {
- self_->SetState(new_thread_state);
- }
+ DCHECK_EQ(self, Thread::Current());
+ // Read state without locks, ok as state is effectively thread local and we're not interested
+ // in the suspend count (this will be handled in the runnable transitions).
+ old_thread_state_ = self->GetStateUnsafe();
+ runnable_transition = old_thread_state_ == kRunnable || new_thread_state == kRunnable;
+ if (!runnable_transition) {
+ // A suspended transition to another effectively suspended transition, ok to use Unsafe.
+ self_->SetStateUnsafe(new_thread_state);
}
if (runnable_transition && old_thread_state_ != new_thread_state) {
if (new_thread_state == kRunnable) {
@@ -68,8 +69,8 @@
} else if (thread_state_ == kRunnable) {
self_->TransitionFromRunnableToSuspended(old_thread_state_);
} else {
- MutexLock mu(*Locks::thread_suspend_count_lock_);
- self_->SetState(old_thread_state_);
+ // A suspended transition to another effectively suspended transition, ok to use Unsafe.
+ self_->SetStateUnsafe(old_thread_state_);
}
}
}