Don't re-read referent in ReferenceProcessor::GetReferent
Re-reading has the issue that it may read a null value after already
having done the null check. Using a cached value prevents this from
happening and causing DCHECK failures.
Added a related stress test.
Bug: 33569625
Bug: 33389022
Test: test-art-host
Change-Id: Ic42d540e035d41ac6e5b01762f9510cd6632b28c
diff --git a/test/153-reference-stress/src/Main.java b/test/153-reference-stress/src/Main.java
new file mode 100644
index 0000000..fc6f9cc
--- /dev/null
+++ b/test/153-reference-stress/src/Main.java
@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2016 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.
+ */
+
+import java.lang.ref.WeakReference;
+
+public class Main {
+ static final int numWeakReferences = 16 * 1024;
+ static WeakReference[] weakReferences = new WeakReference[numWeakReferences];
+ static volatile boolean done = false;
+ static Object keepAlive;
+
+ public static void main(String[] args) throws Exception {
+ // Try to call Reference.get repeatedly while the GC is running.
+ Thread gcThread = new GcThread();
+ Thread[] readerThread = new ReaderThread[4];
+ for (int i = 0; i < readerThread.length; ++i) {
+ readerThread[i] = new ReaderThread();
+ }
+ gcThread.start();
+ for (int i = 0; i < readerThread.length; ++i) {
+ readerThread[i].start();
+ }
+ gcThread.join();
+ for (int i = 0; i < readerThread.length; ++i) {
+ readerThread[i].join();
+ }
+ System.out.println("PASS");
+ }
+
+ static class GcThread extends Thread {
+ GcThread() {
+ Object temp = new Object();
+ for (int j = 0; j < weakReferences.length; ++j) {
+ weakReferences[j] = new WeakReference(temp);
+ }
+ }
+ public void run() {
+ for (int i = 0; i < 1000; ++i) {
+ Object o = new Object();
+ for (int j = 0; j < weakReferences.length; ++j) {
+ weakReferences[j] = new WeakReference(o);
+ }
+ }
+ done = true;
+ }
+ }
+
+ static class ReaderThread extends Thread {
+ public void run() {
+ while (!done) {
+ for (int j = 0; j < weakReferences.length; ++j) {
+ keepAlive = weakReferences[j].get();
+ }
+ for (int j = 0; j < weakReferences.length; ++j) {
+ weakReferences[j].clear();
+ }
+ }
+ }
+ }
+}