8256167: Convert JDK use of Reference::get to Reference::refersTo

Reviewed-by: sspitsyn, shade, dfuchs, alanb, kbarrett

src/java.base/share/classes/java/io/ObjectStreamClass.java

@@ -2411,7 +2411,7 @@ public boolean equals(Object obj) {
                 Class<?> referent;
                 return (nullClass ? other.nullClass
                                   : ((referent = get()) != null) &&
-                                    (referent == other.get())) &&
+                                    (other.refersTo(referent))) &&
                         Arrays.equals(sigs, other.sigs);
             } else {
                 return false;
@@ -2532,9 +2532,9 @@ public boolean equals(Object obj) {
             }
 
             if (obj instanceof WeakClassKey) {
-                Object referent = get();
+                Class<?> referent = get();
                 return (referent != null) &&
-                       (referent == ((WeakClassKey) obj).get());
+                        (((WeakClassKey) obj).refersTo(referent));
             } else {
                 return false;
             }

src/java.base/share/classes/java/lang/Thread.java

@@ -2044,9 +2044,9 @@ public boolean equals(Object obj) {
                 return true;
 
             if (obj instanceof WeakClassKey) {
-                Object referent = get();
+                Class<?> referent = get();
                 return (referent != null) &&
-                       (referent == ((WeakClassKey) obj).get());
+                        (((WeakClassKey) obj).refersTo(referent));
             } else {
                 return false;
             }

src/java.base/share/classes/java/lang/ThreadLocal.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -26,7 +26,7 @@
 package java.lang;
 import jdk.internal.misc.TerminatingThreadLocal;
 
-import java.lang.ref.*;
+import java.lang.ref.WeakReference;
 import java.util.Objects;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Supplier;
@@ -433,7 +433,7 @@ private ThreadLocalMap(ThreadLocalMap parentMap) {
         private Entry getEntry(ThreadLocal<?> key) {
             int i = key.threadLocalHashCode & (table.length - 1);
             Entry e = table[i];
-            if (e != null && e.get() == key)
+            if (e != null && e.refersTo(key))
                 return e;
             else
                 return getEntryAfterMiss(key, i, e);
@@ -453,10 +453,9 @@ private Entry getEntryAfterMiss(ThreadLocal<?> key, int i, Entry e) {
             int len = tab.length;
 
             while (e != null) {
-                ThreadLocal<?> k = e.get();
-                if (k == key)
+                if (e.refersTo(key))
                     return e;
-                if (k == null)
+                if (e.refersTo(null))
                     expungeStaleEntry(i);
                 else
                     i = nextIndex(i, len);
@@ -485,14 +484,12 @@ private void set(ThreadLocal<?> key, Object value) {
             for (Entry e = tab[i];
                  e != null;
                  e = tab[i = nextIndex(i, len)]) {
-                ThreadLocal<?> k = e.get();
-
-                if (k == key) {
+                if (e.refersTo(key)) {
                     e.value = value;
                     return;
                 }
 
-                if (k == null) {
+                if (e.refersTo(null)) {
                     replaceStaleEntry(key, value, i);
                     return;
                 }
@@ -514,7 +511,7 @@ private void remove(ThreadLocal<?> key) {
             for (Entry e = tab[i];
                  e != null;
                  e = tab[i = nextIndex(i, len)]) {
-                if (e.get() == key) {
+                if (e.refersTo(key)) {
                     e.clear();
                     expungeStaleEntry(i);
                     return;
@@ -551,22 +548,20 @@ private void replaceStaleEntry(ThreadLocal<?> key, Object value,
             for (int i = prevIndex(staleSlot, len);
                  (e = tab[i]) != null;
                  i = prevIndex(i, len))
-                if (e.get() == null)
+                if (e.refersTo(null))
                     slotToExpunge = i;
 
             // Find either the key or trailing null slot of run, whichever
             // occurs first
             for (int i = nextIndex(staleSlot, len);
                  (e = tab[i]) != null;
                  i = nextIndex(i, len)) {
-                ThreadLocal<?> k = e.get();
-
                 // If we find key, then we need to swap it
                 // with the stale entry to maintain hash table order.
                 // The newly stale slot, or any other stale slot
                 // encountered above it, can then be sent to expungeStaleEntry
                 // to remove or rehash all of the other entries in run.
-                if (k == key) {
+                if (e.refersTo(key)) {
                     e.value = value;
 
                     tab[i] = tab[staleSlot];
@@ -582,7 +577,7 @@ private void replaceStaleEntry(ThreadLocal<?> key, Object value,
                 // If we didn't find stale entry on backward scan, the
                 // first stale entry seen while scanning for key is the
                 // first still present in the run.
-                if (k == null && slotToExpunge == staleSlot)
+                if (e.refersTo(null) && slotToExpunge == staleSlot)
                     slotToExpunge = i;
             }
 
@@ -673,7 +668,7 @@ private boolean cleanSomeSlots(int i, int n) {
             do {
                 i = nextIndex(i, len);
                 Entry e = tab[i];
-                if (e != null && e.get() == null) {
+                if (e != null && e.refersTo(null)) {
                     n = len;
                     removed = true;
                     i = expungeStaleEntry(i);
@@ -733,7 +728,7 @@ private void expungeStaleEntries() {
             int len = tab.length;
             for (int j = 0; j < len; j++) {
                 Entry e = tab[j];
-                if (e != null && e.get() == null)
+                if (e != null && e.refersTo(null))
                     expungeStaleEntry(j);
             }
         }

src/java.base/share/classes/java/lang/invoke/DirectMethodHandle.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2008, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -402,9 +402,8 @@ private static boolean checkInitialized(MemberName member) {
         if (ref == null) {
             return true;  // the final state
         }
-        Thread clinitThread = ref.get();
         // Somebody may still be running defc.<clinit>.
-        if (clinitThread == Thread.currentThread()) {
+        if (ref.refersTo(Thread.currentThread())) {
             // If anybody is running defc.<clinit>, it is this thread.
             if (UNSAFE.shouldBeInitialized(defc))
                 // Yes, we are running it; keep the barrier for now.

src/java.base/share/classes/java/lang/ref/Reference.java

@@ -337,7 +337,7 @@ public void runFinalization() {
      *
      * @return   The object to which this reference refers, or
      *           {@code null} if this reference object has been cleared
-     * @see refersTo
+     * @see #refersTo
      */
     @IntrinsicCandidate
     public T get() {

src/java.base/share/classes/java/lang/reflect/AccessibleObject.java

@@ -642,7 +642,7 @@ private static class Cache {
         }
 
         boolean isCacheFor(Class<?> caller, Class<?> refc) {
-            return callerRef.get() == caller && targetRef.get() == refc;
+            return callerRef.refersTo(caller) && targetRef.refersTo(refc);
         }
 
         static Object protectedMemberCallerCache(Class<?> caller, Class<?> refc) {
@@ -674,7 +674,7 @@ private boolean isAccessChecked(Class<?> caller) {
         if (cache instanceof WeakReference) {
             @SuppressWarnings("unchecked")
             WeakReference<Class<?>> ref = (WeakReference<Class<?>>) cache;
-            return ref.get() == caller;
+            return ref.refersTo(caller);
         }
         return false;
     }

src/java.base/share/classes/java/util/ResourceBundle.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1996, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1996, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -1755,7 +1755,7 @@ private static ResourceBundle findBundle(Module callerModule,
                 // Otherwise, remove the cached one since we can't keep
                 // the same bundles having different parents.
                 BundleReference bundleRef = cacheList.get(cacheKey);
-                if (bundleRef != null && bundleRef.get() == bundle) {
+                if (bundleRef != null && bundleRef.refersTo(bundle)) {
                     cacheList.remove(cacheKey, bundleRef);
                 }
             }

src/java.base/share/classes/java/util/WeakHashMap.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -27,7 +27,6 @@
 
 import java.lang.ref.WeakReference;
 import java.lang.ref.ReferenceQueue;
-import java.util.concurrent.ThreadLocalRandom;
 import java.util.function.BiConsumer;
 import java.util.function.BiFunction;
 import java.util.function.Consumer;
@@ -283,8 +282,14 @@ static Object unmaskNull(Object key) {
      * Checks for equality of non-null reference x and possibly-null y.  By
      * default uses Object.equals.
      */
-    private static boolean eq(Object x, Object y) {
-        return x == y || x.equals(y);
+    private boolean matchesKey(Entry<K,V> e, Object key) {
+        // check if the given entry refers to the given key without
+        // keeping a strong reference to the entry's referent
+        if (e.refersTo(key)) return true;
+
+        // then check for equality if the referent is not cleared
+        Object k = e.get();
+        return k != null && key.equals(k);
     }
 
     /**
@@ -399,7 +404,7 @@ public V get(Object key) {
         int index = indexFor(h, tab.length);
         Entry<K,V> e = tab[index];
         while (e != null) {
-            if (e.hash == h && eq(k, e.get()))
+            if (e.hash == h && matchesKey(e, k))
                 return e.value;
             e = e.next;
         }
@@ -428,7 +433,7 @@ Entry<K,V> getEntry(Object key) {
         Entry<K,V>[] tab = getTable();
         int index = indexFor(h, tab.length);
         Entry<K,V> e = tab[index];
-        while (e != null && !(e.hash == h && eq(k, e.get())))
+        while (e != null && !(e.hash == h && matchesKey(e, k)))
             e = e.next;
         return e;
     }
@@ -452,7 +457,7 @@ public V put(K key, V value) {
         int i = indexFor(h, tab.length);
 
         for (Entry<K,V> e = tab[i]; e != null; e = e.next) {
-            if (h == e.hash && eq(k, e.get())) {
+            if (h == e.hash && matchesKey(e, k)) {
                 V oldValue = e.value;
                 if (value != oldValue)
                     e.value = value;
@@ -515,8 +520,7 @@ private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) {
             src[j] = null;
             while (e != null) {
                 Entry<K,V> next = e.next;
-                Object key = e.get();
-                if (key == null) {
+                if (e.refersTo(null)) {
                     e.next = null;  // Help GC
                     e.value = null; //  "   "
                     size--;
@@ -597,7 +601,7 @@ public V remove(Object key) {
 
         while (e != null) {
             Entry<K,V> next = e.next;
-            if (h == e.hash && eq(k, e.get())) {
+            if (h == e.hash && matchesKey(e, k)) {
                 modCount++;
                 size--;
                 if (prev == e)

src/java.base/share/classes/jdk/internal/logger/BootstrapLogger.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -181,12 +181,10 @@ static void awaitPendingTasks() {
         // This is used by tests.
         static boolean isAlive() {
             WeakReference<ExecutorService> ref = executorRef;
-            ExecutorService executor = ref == null ? null : ref.get();
-            if (executor != null) return true;
+            if (ref != null && !ref.refersTo(null)) return true;
             synchronized (BootstrapExecutors.class) {
                 ref = executorRef;
-                executor = ref == null ? null : ref.get();
-                return executor != null;
+                return ref != null && !ref.refersTo(null);
             }
         }
 

src/java.logging/share/classes/java/util/logging/LogManager.java

@@ -777,7 +777,7 @@ synchronized boolean addLocalLogger(Logger logger, boolean addDefaultLoggersIfNe
             }
             LoggerWeakRef ref = namedLoggers.get(name);
             if (ref != null) {
-                if (ref.get() == null) {
+                if (ref.refersTo(null)) {
                     // It's possible that the Logger was GC'ed after a
                     // drainLoggerRefQueueBounded() call above so allow
                     // a new one to be registered.

src/java.logging/share/classes/java/util/logging/Logger.java

@@ -2404,8 +2404,7 @@ private void doSetParent(Logger newParent) {
                 // assert parent.kids != null;
                 for (Iterator<LogManager.LoggerWeakRef> iter = parent.kids.iterator(); iter.hasNext(); ) {
                     ref = iter.next();
-                    Logger kid =  ref.get();
-                    if (kid == this) {
+                    if (ref.refersTo(this)) {
                         // ref is used down below to complete the reparenting
                         iter.remove();
                         break;

src/java.management/share/classes/com/sun/jmx/mbeanserver/WeakIdentityHashMap.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2008, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -120,9 +120,10 @@ public boolean equals(Object o) {
                 return true;
             if (!(o instanceof IdentityWeakReference<?>))
                 return false;
-            IdentityWeakReference<?> wr = (IdentityWeakReference<?>) o;
-            Object got = get();
-            return (got != null && got == wr.get());
+            @SuppressWarnings("unchecked")
+            IdentityWeakReference<T> wr = (IdentityWeakReference<T>) o;
+            T got = get();
+            return got != null && wr.refersTo(got);
         }
 
         public int hashCode() {