Add a read barrier for weak roots in monitors.
A weak root requires a read barrier for the to-space invariant to hold
because the object pointed to by a weak root can't be marked/forwarded
like the one pointed to by a strong root (GC does not know if it's
alive or not at that point) and because, without a read barrier, a
mutator could access it and obtain a from-space reference, which would
violate the to-space invariant.
TODO: do similar for the other types of weak roots.
Bug: 12687968
Change-Id: I563a0fa4f875e0c21ac96f57696959454e13b15a
diff --git a/runtime/monitor.h b/runtime/monitor.h
index bc5d2e4..ed1b27b 100644
--- a/runtime/monitor.h
+++ b/runtime/monitor.h
@@ -27,6 +27,7 @@
#include "atomic.h"
#include "base/mutex.h"
#include "object_callbacks.h"
+#include "read_barrier.h"
#include "thread_state.h"
namespace art {
@@ -92,8 +93,9 @@
static bool IsValidLockWord(LockWord lock_word);
+ template<ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
mirror::Object* GetObject() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
- return obj_;
+ return ReadBarrier::BarrierForWeakRoot<mirror::Object, kReadBarrierOption>(obj_);
}
void SetObject(mirror::Object* object);
@@ -190,7 +192,9 @@
// Owner's recursive lock depth.
int lock_count_ GUARDED_BY(monitor_lock_);
- // What object are we part of.
+ // What object are we part of. This is a weak root. Do not access
+ // this directly, use GetObject() to read it so it will be guarded
+ // by a read barrier.
mirror::Object* obj_;
// Threads currently waiting on this monitor.