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
17package com.android.mail.utils;
18
19import android.os.Handler;
20import android.os.Looper;
21import android.os.Message;
22import 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 */
28public 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