Fix race condition in TransitionCollector.
There was a race condition where if multiple threads were calling
TransitionCollector it could cause a crash due to an invalid
collector transition if another thread did the collector transition
before the SuspendAll.
Bug: 13929101
Change-Id: I8c162a83c1f53d0cbdefab62b0a5bcbb151d6c42
diff --git a/runtime/gc/heap.cc b/runtime/gc/heap.cc
index 91f249a..fcf9fe9 100644
--- a/runtime/gc/heap.cc
+++ b/runtime/gc/heap.cc
@@ -1408,6 +1408,13 @@
MutexLock mu(self, *gc_complete_lock_);
// Ensure there is only one GC at a time.
WaitForGcToCompleteLocked(self);
+ // If someone else beat us to it and changed the collector before we could, exit.
+ // This is safe to do before the suspend all since we set the collector_type_running_ before
+ // we exit the loop. If another thread attempts to do the heap transition before we exit,
+ // then it would get blocked on WaitForGcToCompleteLocked.
+ if (collector_type == collector_type_) {
+ return;
+ }
// GC can be disabled if someone has a used GetPrimitiveArrayCritical but not yet released.
if (!copying_transition || disable_moving_gc_count_ == 0) {
// TODO: Not hard code in semi-space collector?