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      1 /*
      2  * Copyright (C) 2012 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.mail.utils;
     18 
     19 import android.os.Handler;
     20 import android.os.Looper;
     21 import android.os.Message;
     22 import android.os.SystemClock;
     23 
     24 /**
     25  * Class to queue tasks.  This delay the specified task by the specified time, up to the maximum
     26  * duration from the time that the first request was received
     27  */
     28 public abstract class DelayedTaskHandler extends Handler {
     29     private final int mDelayMs;
     30 
     31     private static final long UNSET_TIME = -1;
     32 
     33     /**
     34      * Tracks the time when a task was queued, when there had been no pending task.
     35      */
     36     private long mLastTaskExecuteTime = UNSET_TIME;
     37 
     38     public DelayedTaskHandler(Looper looper, int defaultDelayMs) {
     39         super(looper);
     40         mDelayMs = defaultDelayMs;
     41     }
     42 
     43     /**
     44      * Schedule the task to be run after the default delay.
     45      */
     46     public void scheduleTask() {
     47         final long currentTime = SystemClock.elapsedRealtime();
     48         removeMessages(0);
     49         if (mLastTaskExecuteTime == UNSET_TIME ||
     50                 ((mLastTaskExecuteTime + mDelayMs) <  currentTime)) {
     51             // If this is the first task that has been queued or if the last task ran more than
     52             // long enough ago that we don't want to delay this task, run it now
     53             sendEmptyMessage(0);
     54         } else {
     55             // Otherwise delay this task for the specify delay duration
     56             sendEmptyMessageDelayed(0, mDelayMs);
     57         }
     58     }
     59 
     60     @Override
     61     public void dispatchMessage(Message msg) {
     62         onTaskExecution();
     63         performTask();
     64     }
     65 
     66     /**
     67      * Called when the task managed by this handler is executed.  This method can also be called
     68      * to indicate that the task has been started externally.
     69      *
     70      * This updates the handler's internal timestamp.
     71      */
     72     public void onTaskExecution() {
     73         mLastTaskExecuteTime = SystemClock.elapsedRealtime();
     74     }
     75 
     76     /**
     77      * Method to perform the needed task.
     78      */
     79     protected abstract void performTask();
     80 }
     81