123 lines
4.0 KiB
Java
123 lines
4.0 KiB
Java
/*
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* Copyright (C) 2021 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.internal.telephony;
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import android.annotation.IntRange;
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import android.annotation.NonNull;
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import android.os.SystemClock;
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import android.util.LongArrayQueue;
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import com.android.internal.annotations.VisibleForTesting;
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/**
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* Tracks whether an event occurs mNumOccurrences times within the time span mWindowSizeMillis.
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* <p/>
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* Stores all events in memory, use a small number of required occurrences when using.
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*/
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public class SlidingWindowEventCounter {
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private final long mWindowSizeMillis;
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private final int mNumOccurrences;
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private final LongArrayQueue mTimestampQueueMillis;
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public SlidingWindowEventCounter(@IntRange(from = 0) final long windowSizeMillis,
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@IntRange(from = 2) final int numOccurrences) {
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if (windowSizeMillis < 0) {
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throw new IllegalArgumentException("windowSizeMillis must be greater or equal to 0");
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}
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if (numOccurrences <= 1) {
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throw new IllegalArgumentException("numOccurrences must be greater than 1");
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}
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mWindowSizeMillis = windowSizeMillis;
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mNumOccurrences = numOccurrences;
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mTimestampQueueMillis = new LongArrayQueue(numOccurrences);
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}
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/**
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* Increments the occurrence counter.
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*
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* Returns true if an event has occurred at least mNumOccurrences times within the
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* time span mWindowSizeMillis.
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*/
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public synchronized boolean addOccurrence() {
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return addOccurrence(SystemClock.elapsedRealtime());
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}
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/**
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* Increments the occurrence counter.
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*
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* Returns true if an event has occurred at least mNumOccurrences times within the
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* time span mWindowSizeMillis.
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* @param timestampMillis
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*/
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public synchronized boolean addOccurrence(long timestampMillis) {
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mTimestampQueueMillis.addLast(timestampMillis);
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if (mTimestampQueueMillis.size() > mNumOccurrences) {
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mTimestampQueueMillis.removeFirst();
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}
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return isInWindow();
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}
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/**
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* Returns true if the conditions is satisfied.
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*/
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public synchronized boolean isInWindow() {
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return (mTimestampQueueMillis.size() == mNumOccurrences)
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&& mTimestampQueueMillis.peekFirst()
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+ mWindowSizeMillis > mTimestampQueueMillis.peekLast();
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}
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@VisibleForTesting
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int getQueuedNumOccurrences() {
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return mTimestampQueueMillis.size();
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}
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/**
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* @return the time span in ms of the sliding window.
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*/
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public synchronized long getWindowSizeMillis() {
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return mWindowSizeMillis;
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}
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/**
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* @return the least number of occurrences for {@link #isInWindow} to be true.
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*/
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public synchronized int getNumOccurrences() {
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return mNumOccurrences;
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}
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/**
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* Get the event frequency description.
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*
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* @return A string describing the anomaly event
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*/
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public @NonNull String getFrequencyString() {
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if (mWindowSizeMillis >= 1000L) {
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return mNumOccurrences + " times within " + mWindowSizeMillis / 1000L + " seconds";
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} else {
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return mNumOccurrences + " times within " + mWindowSizeMillis + "ms";
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}
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}
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@Override
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public String toString() {
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return String.format("SlidingWindowEventCounter=[windowSizeMillis=" + mWindowSizeMillis
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+ ", numOccurrences=" + mNumOccurrences
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+ ", timestampQueueMillis=" + mTimestampQueueMillis + "]");
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}
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}
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