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      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 {
     54         boolean postDelayed(Runnable runnable, long delayMillis);
     55         void removeCallbacks(Runnable runnable);
     56     }
     57 
     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 
     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}. */
     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. */
     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. */
     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. */
    106     public long getCurrentDelay() {
    107         return mCurrentDelayMs;
    108     }
    109 
    110     @VisibleForTesting
    111     public void setHandlerAdapter(HandlerAdapter a) {
    112         mHandlerAdapter  = a;
    113     }
    114 }
    115