Index: base/android/java/src/org/chromium/base/ReferencePool.java |
diff --git a/base/android/java/src/org/chromium/base/ReferencePool.java b/base/android/java/src/org/chromium/base/ReferencePool.java |
new file mode 100644 |
index 0000000000000000000000000000000000000000..37bd8b529527455a33757e0d6c5cdd50a62fce7d |
--- /dev/null |
+++ b/base/android/java/src/org/chromium/base/ReferencePool.java |
@@ -0,0 +1,69 @@ |
+// Copyright 2017 The Chromium Authors. All rights reserved. |
+// Use of this source code is governed by a BSD-style license that can be |
+// found in the LICENSE file. |
+ |
+package org.chromium.base; |
+ |
+import android.support.annotation.Nullable; |
+ |
+import java.lang.ref.WeakReference; |
+import java.util.WeakHashMap; |
+ |
+/** |
+ * A ReferencePool allows handing out typed references to objects ("payloads") that can be dropped |
+ * in one batch ("drained"), e.g. under memory pressure. In contrast to {@link WeakReference}s, |
+ * which drop their referents when they get garbage collected, a reference pool gives more precise |
+ * control over when exactly it is drained. |
+ * |
+ * <p>Internally it uses a {@link WeakHashMap} with the reference itself as a key to allow the |
+ * payloads to be garbage collected regularly when the last reference goes away before the pool is |
+ * drained. |
+ * |
+ * <p>Note that certain kinds of reference cycles that would be garbage-collected when using weak |
+ * (or even strong) references could lead to leaks with a ReferencePool: For example, if a |
+ * {@link Reference} is held by its own payload (including indirectly) but is otherwise not |
+ * referenced, it will not get garbage-collected, because the ReferencePool will still hold a strong |
+ * reference to the payload. |
+ */ |
+public class ReferencePool { |
rmcilroy
2017/05/10 14:38:11
nit - not sure about the name. How about Discardab
Bernhard Bauer
2017/05/10 17:47:50
Good idea! Done. I kept variable and member names
|
+ /** |
+ * The underlying data storage. The wildcard type parameter allows using a single pool for |
+ * references of any type. |
+ */ |
+ private final WeakHashMap<Reference<?>, Object> mPool = new WeakHashMap<>(); |
+ |
+ /** |
+ * A reference to an object in the pool. Will be nulled out when the pool has been drained. |
+ * @param <T> The type of the object. |
+ */ |
+ public class Reference<T> { |
rmcilroy
2017/05/10 14:38:11
nit - DiscardableReference to make it clear it cou
Bernhard Bauer
2017/05/10 17:47:50
Done.
|
+ /** |
+ * @return The referent, or null if the pool has been drained. |
+ */ |
+ @SuppressWarnings("unchecked") |
+ @Nullable |
+ public T get() { |
+ return (T) mPool.get(this); |
+ } |
+ } |
+ |
+ /** |
+ * @param <T> The type of the object. |
+ * @param payload The payload to add to the pool. |
+ * @return A new reference to the {@code payload}. |
+ */ |
+ public <T> Reference<T> put(T payload) { |
+ assert payload != null; |
+ Reference<T> reference = new Reference<>(); |
+ mPool.put(reference, payload); |
+ return reference; |
+ } |
+ |
+ /** |
+ * Drains the pool, removing all references to objects in the pool and therefore allowing them |
+ * to be garbage collected. |
+ */ |
+ public void drain() { |
+ mPool.clear(); |
+ } |
+} |