Updatable.java revision 12f608f3d2089439a108788a1908941eea4277b9 
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
19/**
20 * A thread-safe callback.
21 * <p>
22 * Depending on how consumers need to access updates, the following
23 * implementations may be used (and already guarantee thread-safety):
24 * <ul>
25 * <li>Synchronous access to every update: {@link ConcurrentBufferQueue}</li>
26 * <li>Synchronous access to a single update: {@link UpdatableCountDownLatch}</li>
27 * <li>Access to the latest value: {@link ConcurrentState}</li>
28 * <li>Callbacks: {@link ConcurrentState}</li>
29 * </ul>
30 * </p>
31 */
32public interface Updatable<T> {
33    /**
34     * Implementations MUST ALWAYS satisfy the following constraints:
35     * <ul>
36     * <li>Return quickly, without performing any expensive work.</li>
37     * <li>Execute in a predictable, stable, amount of time.</li>
38     * <li>Never block.</li>
39     * <li>Be thread-safe.</li>
40     * <li>Never leak control of the thread on which they are invoked. (e.g.
41     * invoke callbacks which may violate the above constraints)</li>
42     * </ul>
43     */
44    public void update(T t);
45}
46