Updatable.java revision 4961ad31d9a877e3a68566fb5d4b33b7f79ce44e 
1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.camera.async;
18
19import javax.annotation.Nonnull;
20import javax.annotation.concurrent.ThreadSafe;
21
22/**
23 * A thread-safe callback.
24 * <p>
25 * Depending on how consumers need to access updates, the following
26 * implementations may be used (and already guarantee thread-safety):
27 * <ul>
28 * <li>Synchronous access to every update: {@link ConcurrentBufferQueue}</li>
29 * <li>Synchronous access to a single update: {@link UpdatableCountDownLatch}</li>
30 * <li>Access to the latest value: {@link ConcurrentState}</li>
31 * <li>Callbacks: {@link ConcurrentState}</li>
32 * </ul>
33 * </p>
34 */
35@ThreadSafe
36public interface Updatable<T> {
37    /**
38     * Implementations MUST ALWAYS satisfy the following constraints:
39     * <ul>
40     * <li>Return quickly, without performing any expensive work.</li>
41     * <li>Execute in a predictable, stable, amount of time.</li>
42     * <li>Never block.</li>
43     * <li>Be thread-safe.</li>
44     * <li>Never leak control of the thread on which they are invoked. (e.g.
45     * invoke callbacks which may violate the above constraints)</li>
46     * </ul>
47     */
48    public void update(@Nonnull T t);
49}
50