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      1 /*
      2  * Copyright (C) 2008 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 
     17 package com.android.launcher3;
     18 
     19 import android.os.Handler;
     20 import android.os.Looper;
     21 import android.os.Message;
     22 import android.os.MessageQueue;
     23 
     24 import com.android.launcher3.util.Thunk;
     25 
     26 import java.util.LinkedList;
     27 
     28 /**
     29  * Queue of things to run on a looper thread.  Items posted with {@link #post} will not
     30  * be actually enqued on the handler until after the last one has run, to keep from
     31  * starving the thread.
     32  *
     33  * This class is fifo.
     34  */
     35 public class DeferredHandler {
     36     @Thunk LinkedList<Runnable> mQueue = new LinkedList<>();
     37     private MessageQueue mMessageQueue = Looper.myQueue();
     38     private Impl mHandler = new Impl();
     39 
     40     @Thunk class Impl extends Handler implements MessageQueue.IdleHandler {
     41         public void handleMessage(Message msg) {
     42             Runnable r;
     43             synchronized (mQueue) {
     44                 if (mQueue.size() == 0) {
     45                     return;
     46                 }
     47                 r = mQueue.removeFirst();
     48             }
     49             r.run();
     50             synchronized (mQueue) {
     51                 scheduleNextLocked();
     52             }
     53         }
     54 
     55         public boolean queueIdle() {
     56             handleMessage(null);
     57             return false;
     58         }
     59     }
     60 
     61     private class IdleRunnable implements Runnable {
     62         Runnable mRunnable;
     63 
     64         IdleRunnable(Runnable r) {
     65             mRunnable = r;
     66         }
     67 
     68         public void run() {
     69             mRunnable.run();
     70         }
     71     }
     72 
     73     public DeferredHandler() {
     74     }
     75 
     76     /** Schedule runnable to run after everything that's on the queue right now. */
     77     public void post(Runnable runnable) {
     78         synchronized (mQueue) {
     79             mQueue.add(runnable);
     80             if (mQueue.size() == 1) {
     81                 scheduleNextLocked();
     82             }
     83         }
     84     }
     85 
     86     /** Schedule runnable to run when the queue goes idle. */
     87     public void postIdle(final Runnable runnable) {
     88         post(new IdleRunnable(runnable));
     89     }
     90 
     91     public void cancelAll() {
     92         synchronized (mQueue) {
     93             mQueue.clear();
     94         }
     95     }
     96 
     97     /** Runs all queued Runnables from the calling thread. */
     98     public void flush() {
     99         LinkedList<Runnable> queue = new LinkedList<>();
    100         synchronized (mQueue) {
    101             queue.addAll(mQueue);
    102             mQueue.clear();
    103         }
    104         for (Runnable r : queue) {
    105             r.run();
    106         }
    107     }
    108 
    109     void scheduleNextLocked() {
    110         if (mQueue.size() > 0) {
    111             Runnable peek = mQueue.getFirst();
    112             if (peek instanceof IdleRunnable) {
    113                 mMessageQueue.addIdleHandler(mHandler);
    114             } else {
    115                 mHandler.sendEmptyMessage(1);
    116             }
    117         }
    118     }
    119 }
    120 
    121