Fix object identity hash.
The object identity hash is now stored in the monitor word after
being computed. Hashes are computed by a pseudo random number
generator.
When we write the image, we eagerly compute object hashes to
prevent pages getting dirtied.
Bug: 8981901
Change-Id: Ic8edacbacb0afc7055fd740a52444929f88ed564
diff --git a/runtime/mirror/object.cc b/runtime/mirror/object.cc
index 92c05b2..49bad4c 100644
--- a/runtime/mirror/object.cc
+++ b/runtime/mirror/object.cc
@@ -14,6 +14,8 @@
* limitations under the License.
*/
+#include <ctime>
+
#include "object.h"
#include "art_field.h"
@@ -82,6 +84,52 @@
return copy.get();
}
+uint32_t Object::GenerateIdentityHashCode() {
+ static AtomicInteger seed(987654321 + std::time(nullptr));
+ uint32_t expected_value, new_value;
+ do {
+ expected_value = static_cast<uint32_t>(seed.load());
+ new_value = expected_value * 1103515245 + 12345;
+ } while (!seed.compare_and_swap(static_cast<int32_t>(expected_value),
+ static_cast<int32_t>(new_value)));
+ return expected_value & LockWord::kHashMask;
+}
+
+int32_t Object::IdentityHashCode() const {
+ while (true) {
+ LockWord lw = GetLockWord();
+ switch (lw.GetState()) {
+ case LockWord::kUnlocked: {
+ // Try to compare and swap in a new hash, if we succeed we will return the hash on the next
+ // loop iteration.
+ LockWord hash_word(LockWord::FromHashCode(GenerateIdentityHashCode()));
+ DCHECK_EQ(hash_word.GetState(), LockWord::kHashCode);
+ if (const_cast<Object*>(this)->CasLockWord(lw, hash_word)) {
+ return hash_word.GetHashCode();
+ }
+ break;
+ }
+ case LockWord::kThinLocked: {
+ // Inflate the thin lock to a monitor and stick the hash code inside of the monitor.
+ Thread* self = Thread::Current();
+ Monitor::InflateThinLocked(self, const_cast<Object*>(this), lw, GenerateIdentityHashCode());
+ break;
+ }
+ case LockWord::kFatLocked: {
+ // Already inflated, return the has stored in the monitor.
+ Monitor* monitor = lw.FatLockMonitor();
+ DCHECK(monitor != nullptr);
+ return monitor->GetHashCode();
+ }
+ case LockWord::kHashCode: {
+ return lw.GetHashCode();
+ }
+ }
+ }
+ LOG(FATAL) << "Unreachable";
+ return 0;
+}
+
void Object::CheckFieldAssignmentImpl(MemberOffset field_offset, const Object* new_value) {
const Class* c = GetClass();
if (Runtime::Current()->GetClassLinker() == NULL ||