| /* |
| * Copyright (C) 2016 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.server.notification; |
| |
| |
| /** |
| * Exponentially weighted moving average estimator for event rate. |
| * |
| * {@hide} |
| */ |
| public class RateEstimator { |
| private static final double RATE_ALPHA = 0.8; |
| private static final double MINIMUM_DT = 0.0005; |
| private Long mLastEventTime; |
| private double mInterarrivalTime; |
| |
| public RateEstimator() { |
| // assume something generous if we have no information |
| mInterarrivalTime = 1000.0; |
| } |
| |
| /** Update the estimate to account for an event that just happened. */ |
| public float update(long now) { |
| float rate; |
| if (mLastEventTime == null) { |
| // No last event time, rate is zero. |
| rate = 0f; |
| } else { |
| // Calculate the new inter-arrival time based on last event time. |
| mInterarrivalTime = getInterarrivalEstimate(now); |
| rate = (float) (1.0 / mInterarrivalTime); |
| } |
| mLastEventTime = now; |
| return rate; |
| } |
| |
| /** @return the estimated rate if there were a new event right now. */ |
| public float getRate(long now) { |
| if (mLastEventTime == null) { |
| return 0f; |
| } |
| return (float) (1.0 / getInterarrivalEstimate(now)); |
| } |
| |
| /** @return the average inter-arrival time if there were a new event right now. */ |
| private double getInterarrivalEstimate(long now) { |
| double dt = ((double) (now - mLastEventTime)) / 1000.0; |
| dt = Math.max(dt, MINIMUM_DT); |
| // a*iat_old + (1-a)*(t_now-t_last) |
| return (RATE_ALPHA * mInterarrivalTime + (1.0 - RATE_ALPHA) * dt); |
| } |
| } |