Add concurrent reference processing.

Concurrent reference processing currently works by going into native
code from java.lang.ref.Reference.get(). From there, we have a fast
path if the references aren't being processed which returns the
referent without needing to access any locks. In the slow path we
block until reference processing is complete. It may be possible to
improve the slow path if the referent is blackened.

TODO: Investigate doing the fast path in java code by using racy reads
of a static volatile boolean. This will work as long as there are no
suspend points inbetween the boolean read and referent read.

Bug: 14381653

Change-Id: I1546b55be4691fe4ff4aa6d857b234cce7187d87

1 files changed, 42 insertions, 0 deletions

diff --git a/runtime/native/java_lang_ref_Reference.cc b/runtime/native/java_lang_ref_Reference.cc
new file mode 100644
index 0000000000..f221ac60f5
--- /dev/null
+++ b/runtime/native/java_lang_ref_Reference.cc
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "gc/heap.h"
+#include "gc/reference_processor.h"
+#include "jni_internal.h"
+#include "mirror/object-inl.h"
+#include "mirror/reference-inl.h"
+#include "scoped_fast_native_object_access.h"
+
+namespace art {
+
+static jobject Reference_get(JNIEnv* env, jobject javaThis) {
+  ScopedFastNativeObjectAccess soa(env);
+  mirror::Reference* const ref = soa.Decode<mirror::Reference*>(javaThis);
+  mirror::Object* const referent =
+      Runtime::Current()->GetHeap()->GetReferenceProcessor()->GetReferent(soa.Self(), ref);
+  return soa.AddLocalReference<jobject>(referent);
+}
+
+static JNINativeMethod gMethods[] = {
+  NATIVE_METHOD(Reference, get, "!()Ljava/lang/Object;"),
+};
+
+void register_java_lang_ref_Reference(JNIEnv* env) {
+  REGISTER_NATIVE_METHODS("java/lang/ref/Reference");
+}
+
+}  // namespace art