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/*
* Copyright (C) 2023 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.testutils.async;
import com.android.net.module.util.async.OsAccess;
import java.util.Arrays;
/**
* Limits the number of bytes processed to the given maximum of bytes per second.
*
* The limiter tracks the total for the past second, along with sums for each 10ms
* in the past second, allowing the total to be adjusted as the time passes.
*/
public final class RateLimiter {
private static final int PERIOD_DURATION_MS = 1000;
private static final int BUCKET_COUNT = 100;
public static final int BUCKET_DURATION_MS = PERIOD_DURATION_MS / BUCKET_COUNT;
private final OsAccess mOsAccess;
private final int[] mStatBuckets = new int[BUCKET_COUNT];
private int mMaxPerPeriodBytes;
private int mMaxPerBucketBytes;
private int mRecordedPeriodBytes;
private long mLastLimitTimestamp;
private int mLastRequestReduction;
public RateLimiter(OsAccess osAccess, int bytesPerSecond) {
mOsAccess = osAccess;
setBytesPerSecond(bytesPerSecond);
clear();
}
public int getBytesPerSecond() {
return mMaxPerPeriodBytes;
}
public void setBytesPerSecond(int bytesPerSecond) {
mMaxPerPeriodBytes = bytesPerSecond;
mMaxPerBucketBytes = Math.max(1, (mMaxPerPeriodBytes / BUCKET_COUNT) * 2);
}
public void clear() {
mLastLimitTimestamp = mOsAccess.monotonicTimeMillis();
mRecordedPeriodBytes = 0;
Arrays.fill(mStatBuckets, 0);
}
public static int limit(RateLimiter limiter1, RateLimiter limiter2, int requestedBytes) {
final long now = limiter1.mOsAccess.monotonicTimeMillis();
final int allowedCount = Math.min(limiter1.calculateLimit(now, requestedBytes),
limiter2.calculateLimit(now, requestedBytes));
limiter1.recordBytes(now, requestedBytes, allowedCount);
limiter2.recordBytes(now, requestedBytes, allowedCount);
return allowedCount;
}
public int limit(int requestedBytes) {
final long now = mOsAccess.monotonicTimeMillis();
final int allowedCount = calculateLimit(now, requestedBytes);
recordBytes(now, requestedBytes, allowedCount);
return allowedCount;
}
public int getLastRequestReduction() {
return mLastRequestReduction;
}
public boolean acceptAllOrNone(int requestedBytes) {
final long now = mOsAccess.monotonicTimeMillis();
final int allowedCount = calculateLimit(now, requestedBytes);
if (allowedCount < requestedBytes) {
return false;
}
recordBytes(now, requestedBytes, allowedCount);
return true;
}
private int calculateLimit(long now, int requestedBytes) {
// First remove all stale bucket data and adjust the total.
final long currentBucketAbsIdx = now / BUCKET_DURATION_MS;
final long staleCutoffIdx = currentBucketAbsIdx - BUCKET_COUNT;
for (long i = mLastLimitTimestamp / BUCKET_DURATION_MS; i < staleCutoffIdx; i++) {
final int idx = (int) (i % BUCKET_COUNT);
mRecordedPeriodBytes -= mStatBuckets[idx];
mStatBuckets[idx] = 0;
}
final int bucketIdx = (int) (currentBucketAbsIdx % BUCKET_COUNT);
final int maxAllowed = Math.min(mMaxPerPeriodBytes - mRecordedPeriodBytes,
Math.min(mMaxPerBucketBytes - mStatBuckets[bucketIdx], requestedBytes));
return Math.max(0, maxAllowed);
}
private void recordBytes(long now, int requestedBytes, int actualBytes) {
mStatBuckets[(int) ((now / BUCKET_DURATION_MS) % BUCKET_COUNT)] += actualBytes;
mRecordedPeriodBytes += actualBytes;
mLastRequestReduction = requestedBytes - actualBytes;
mLastLimitTimestamp = now;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("{max=");
sb.append(mMaxPerPeriodBytes);
sb.append(",max_bucket=");
sb.append(mMaxPerBucketBytes);
sb.append(",total=");
sb.append(mRecordedPeriodBytes);
sb.append(",last_red=");
sb.append(mLastRequestReduction);
sb.append('}');
return sb.toString();
}
}
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