/* * Copyright (C) 2006 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 android.os; import android.util.Log; import android.util.Printer; import android.util.PrefixPrinter; /** * Class used to run a message loop for a thread. Threads by default do * not have a message loop associated with them; to create one, call * {@link #prepare} in the thread that is to run the loop, and then * {@link #loop} to have it process messages until the loop is stopped. * *
Most interaction with a message loop is through the * {@link Handler} class. * *
This is a typical example of the implementation of a Looper thread, * using the separation of {@link #prepare} and {@link #loop} to create an * initial Handler to communicate with the Looper. * *
* class LooperThread extends Thread { * public Handler mHandler; * * public void run() { * Looper.prepare(); * * mHandler = new Handler() { * public void handleMessage(Message msg) { * // process incoming messages here * } * }; * * Looper.loop(); * } * }*/ public final class Looper { private static final String TAG = "Looper"; // sThreadLocal.get() will return null unless you've called prepare(). static final ThreadLocal
* Causes the {@link #loop} method to terminate without processing any * more messages in the message queue. *
* Any attempt to post messages to the queue after the looper is asked to quit will fail. * For example, the {@link Handler#sendMessage(Message)} method will return false. *
* Using this method may be unsafe because some messages may not be delivered * before the looper terminates. Consider using {@link #quitSafely} instead to ensure * that all pending work is completed in an orderly manner. *
* * @see #quitSafely */ public void quit() { mQueue.quit(false); } /** * Quits the looper safely. ** Causes the {@link #loop} method to terminate as soon as all remaining messages * in the message queue that are already due to be delivered have been handled. * However pending delayed messages with due times in the future will not be * delivered before the loop terminates. *
* Any attempt to post messages to the queue after the looper is asked to quit will fail. * For example, the {@link Handler#sendMessage(Message)} method will return false. *
*/ public void quitSafely() { mQueue.quit(true); } /** * Posts a synchronization barrier to the Looper's message queue. * * Message processing occurs as usual until the message queue encounters the * synchronization barrier that has been posted. When the barrier is encountered, * later synchronous messages in the queue are stalled (prevented from being executed) * until the barrier is released by calling {@link #removeSyncBarrier} and specifying * the token that identifies the synchronization barrier. * * This method is used to immediately postpone execution of all subsequently posted * synchronous messages until a condition is met that releases the barrier. * Asynchronous messages (see {@link Message#isAsynchronous} are exempt from the barrier * and continue to be processed as usual. * * This call must be always matched by a call to {@link #removeSyncBarrier} with * the same token to ensure that the message queue resumes normal operation. * Otherwise the application will probably hang! * * @return A token that uniquely identifies the barrier. This token must be * passed to {@link #removeSyncBarrier} to release the barrier. * * @hide */ public int postSyncBarrier() { return mQueue.enqueueSyncBarrier(SystemClock.uptimeMillis()); } /** * Removes a synchronization barrier. * * @param token The synchronization barrier token that was returned by * {@link #postSyncBarrier}. * * @throws IllegalStateException if the barrier was not found. * * @hide */ public void removeSyncBarrier(int token) { mQueue.removeSyncBarrier(token); } /** * Return the Thread associated with this Looper. */ public Thread getThread() { return mThread; } /** @hide */ public MessageQueue getQueue() { return mQueue; } /** * Return whether this looper's thread is currently idle, waiting for new work * to do. This is intrinsically racy, since its state can change before you get * the result back. * @hide */ public boolean isIdling() { return mQueue.isIdling(); } public void dump(Printer pw, String prefix) { pw = PrefixPrinter.create(pw, prefix); pw.println(this.toString()); pw.println("mRun=" + mRun); pw.println("mThread=" + mThread); pw.println("mQueue=" + ((mQueue != null) ? mQueue : "(null")); if (mQueue != null) { synchronized (mQueue) { long now = SystemClock.uptimeMillis(); Message msg = mQueue.mMessages; int n = 0; while (msg != null) { pw.println(" Message " + n + ": " + msg.toString(now)); n++; msg = msg.next; } pw.println("(Total messages: " + n + ")"); } } } public String toString() { return "Looper{" + Integer.toHexString(System.identityHashCode(this)) + "}"; } }