src/com/android/camera/async/Updatable.java

/*
 * Copyright (C) 2014 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.
 */

package com.android.camera.async;

/**
 * An interface for updating thread-shared state from producer threads with
 * real-time requirements.
 * <p>
 * Depending on how consumers need to access updates, the following
 * implementations may be used:
 * <ul>
 * <li>Synchronous access to every update: {@link ConcurrentBufferQueue}</li>
 * <li>Synchronous access to a single update: {@link UpdatableCountDownLatch}</li>
 * <li>Polling: {@link ConcurrentState}</li>
 * <li>Callbacks: {@link ConcurrentState}</li>
 * </ul>
 * </p>
 */
public interface Updatable<T> {
    /**
     * Implementations MUST ALWAYS satisfy the following constraints:
     * <ul>
     * <li>Return quickly, without performing any expensive work.</li>
     * <li>Execute in a predictable, stable, amount of time.</li>
     * <li>Never block.</li>
     * <li>Be thread-safe.</li>
     * <li>Never leak control of the thread on which they are invoked. (e.g.
     * invoke callbacks which may violate the above constraints)</li>
     * </ul>
     */
    public void update(T t);
}