Move ExponentialBackoff to frameworks/base

/*

 * Copyright (C) 2017 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.android.internal.telephony;

import android.annotation.NonNull;

import android.os.Handler;

import android.os.Looper;

/** The implementation of exponential backoff with jitter applied. */

public class ExponentialBackoff {

    private int mRetryCounter;

    private long mStartDelayMs;

    private long mMaximumDelayMs;

    private long mCurrentDelayMs;

    private int mMultiplier;

    private Runnable mRunnable;

    private Handler mHandler;

    public ExponentialBackoff(

            long initialDelayMs,

            long maximumDelayMs,

            int multiplier,

            @NonNull Looper looper,

            @NonNull Runnable runnable) {

        this(initialDelayMs, maximumDelayMs, multiplier, new Handler(looper), runnable);

    }

    public ExponentialBackoff(

            long initialDelayMs,

            long maximumDelayMs,

            int multiplier,

            @NonNull Handler handler,

            @NonNull Runnable runnable) {

        mRetryCounter = 0;

        mStartDelayMs = initialDelayMs;

        mMaximumDelayMs = maximumDelayMs;

        mMultiplier = multiplier;

        mHandler = handler;

        mRunnable = runnable;

    }

    /** Starts the backoff, the runnable will be executed after {@link #mStartDelayMs}. */

    public void start() {

        mRetryCounter = 0;

        mCurrentDelayMs = mStartDelayMs;

        mHandler.removeCallbacks(mRunnable);

        mHandler.postDelayed(mRunnable, mCurrentDelayMs);

    }

    /** Stops the backoff, all pending messages will be removed from the message queue. */

    public void stop() {

        mRetryCounter = 0;

        mHandler.removeCallbacks(mRunnable);

    }

    /** Should call when the retry action has failed and we want to retry after a longer delay. */

    public void notifyFailed() {

        mRetryCounter++;

        long temp = Math.min(

                mMaximumDelayMs, (long) (mStartDelayMs * Math.pow(mMultiplier, mRetryCounter)));

        mCurrentDelayMs = (long) (((1 + Math.random()) / 2) * temp);

        mHandler.removeCallbacks(mRunnable);

        mHandler.postDelayed(mRunnable, mCurrentDelayMs);

    }

    /** Returns the delay for the most recently posted message. */

    public long getCurrentDelay() {

        return mCurrentDelayMs;

    }

}