1 /*
2  * Copyright (C) 2017 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.internal.telephony;
18 
19 import android.annotation.NonNull;
20 import android.os.Handler;
21 import android.os.Looper;
22 
23 import com.android.internal.annotations.VisibleForTesting;
24 
25 /** The implementation of exponential backoff with jitter applied. */
26 public class ExponentialBackoff {
27     private int mRetryCounter;
28     private long mStartDelayMs;
29     private long mMaximumDelayMs;
30     private long mCurrentDelayMs;
31     private int mMultiplier;
32     private final Runnable mRunnable;
33     private final Handler mHandler;
34 
35     /**
36      * Implementation of Handler methods, Adapter for testing (can't spy on final methods).
37      */
38     private HandlerAdapter mHandlerAdapter = new HandlerAdapter() {
39         @Override
40         public boolean postDelayed(Runnable runnable, long delayMillis) {
41             return mHandler.postDelayed(runnable, delayMillis);
42         }
43 
44         @Override
45         public void removeCallbacks(Runnable runnable) {
46             mHandler.removeCallbacks(runnable);
47         }
48     };
49 
50     /**
51      * Need to spy final methods for testing.
52      */
53     public interface HandlerAdapter {
postDelayed(Runnable runnable, long delayMillis)54         boolean postDelayed(Runnable runnable, long delayMillis);
removeCallbacks(Runnable runnable)55         void removeCallbacks(Runnable runnable);
56     }
57 
ExponentialBackoff( long initialDelayMs, long maximumDelayMs, int multiplier, @NonNull Looper looper, @NonNull Runnable runnable)58     public ExponentialBackoff(
59             long initialDelayMs,
60             long maximumDelayMs,
61             int multiplier,
62             @NonNull Looper looper,
63             @NonNull Runnable runnable) {
64         this(initialDelayMs, maximumDelayMs, multiplier, new Handler(looper), runnable);
65     }
66 
ExponentialBackoff( long initialDelayMs, long maximumDelayMs, int multiplier, @NonNull Handler handler, @NonNull Runnable runnable)67     public ExponentialBackoff(
68             long initialDelayMs,
69             long maximumDelayMs,
70             int multiplier,
71             @NonNull Handler handler,
72             @NonNull Runnable runnable) {
73         mRetryCounter = 0;
74         mStartDelayMs = initialDelayMs;
75         mMaximumDelayMs = maximumDelayMs;
76         mMultiplier = multiplier;
77         mHandler = handler;
78         mRunnable = runnable;
79     }
80 
81     /** Starts the backoff, the runnable will be executed after {@link #mStartDelayMs}. */
start()82     public void start() {
83         mRetryCounter = 0;
84         mCurrentDelayMs = mStartDelayMs;
85         mHandlerAdapter.removeCallbacks(mRunnable);
86         mHandlerAdapter.postDelayed(mRunnable, mCurrentDelayMs);
87     }
88 
89     /** Stops the backoff, all pending messages will be removed from the message queue. */
stop()90     public void stop() {
91         mRetryCounter = 0;
92         mHandlerAdapter.removeCallbacks(mRunnable);
93     }
94 
95     /** Should call when the retry action has failed and we want to retry after a longer delay. */
notifyFailed()96     public void notifyFailed() {
97         mRetryCounter++;
98         long temp = Math.min(
99                 mMaximumDelayMs, (long) (mStartDelayMs * Math.pow(mMultiplier, mRetryCounter)));
100         mCurrentDelayMs = (long) (((1 + Math.random()) / 2) * temp);
101         mHandlerAdapter.removeCallbacks(mRunnable);
102         mHandlerAdapter.postDelayed(mRunnable, mCurrentDelayMs);
103     }
104 
105     /** Returns the delay for the most recently posted message. */
getCurrentDelay()106     public long getCurrentDelay() {
107         return mCurrentDelayMs;
108     }
109 
110     @VisibleForTesting
setHandlerAdapter(HandlerAdapter a)111     public void setHandlerAdapter(HandlerAdapter a) {
112         mHandlerAdapter  = a;
113     }
114 }
115