PercentileTimeToFirstByteEstimator.java
/*
* Copyright 2021 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 androidx.media3.exoplayer.upstream.experimental;
import static androidx.media3.common.util.Assertions.checkArgument;
import androidx.annotation.Nullable;
import androidx.annotation.VisibleForTesting;
import androidx.media3.common.C;
import androidx.media3.common.util.Clock;
import androidx.media3.common.util.UnstableApi;
import androidx.media3.common.util.Util;
import androidx.media3.datasource.DataSpec;
import androidx.media3.exoplayer.upstream.SlidingPercentile;
import androidx.media3.exoplayer.upstream.TimeToFirstByteEstimator;
import java.util.LinkedHashMap;
import java.util.Map;
/**
* Implementation of {@link TimeToFirstByteEstimator} that returns a configured percentile of a
* sliding window of collected response times.
*/
@UnstableApi
public final class PercentileTimeToFirstByteEstimator implements TimeToFirstByteEstimator {
/** The default maximum number of samples. */
public static final int DEFAULT_MAX_SAMPLES_COUNT = 10;
/** The default percentile to return. */
public static final float DEFAULT_PERCENTILE = 0.5f;
private static final int MAX_DATA_SPECS = 10;
private final LinkedHashMap<DataSpec, Long> initializedDataSpecs;
private final SlidingPercentile slidingPercentile;
private final float percentile;
private final Clock clock;
private boolean isEmpty;
/**
* Creates an instance that keeps up to {@link #DEFAULT_MAX_SAMPLES_COUNT} samples and returns the
* {@link #DEFAULT_PERCENTILE} percentile.
*/
public PercentileTimeToFirstByteEstimator() {
this(DEFAULT_MAX_SAMPLES_COUNT, DEFAULT_PERCENTILE);
}
/**
* Creates an instance.
*
* @param numberOfSamples The maximum number of samples to be kept in the sliding window.
* @param percentile The percentile for estimating the time to the first byte.
*/
public PercentileTimeToFirstByteEstimator(int numberOfSamples, float percentile) {
this(numberOfSamples, percentile, Clock.DEFAULT);
}
/**
* Creates an instance.
*
* @param numberOfSamples The maximum number of samples to be kept in the sliding window.
* @param percentile The percentile for estimating the time to the first byte.
* @param clock The {@link Clock} to use.
*/
@VisibleForTesting
/* package */ PercentileTimeToFirstByteEstimator(
int numberOfSamples, float percentile, Clock clock) {
checkArgument(numberOfSamples > 0 && percentile > 0 && percentile <= 1);
this.percentile = percentile;
this.clock = clock;
initializedDataSpecs = new FixedSizeLinkedHashMap<>(/* maxSize= */ MAX_DATA_SPECS);
slidingPercentile = new SlidingPercentile(/* maxWeight= */ numberOfSamples);
isEmpty = true;
}
@Override
public long getTimeToFirstByteEstimateUs() {
return !isEmpty ? (long) slidingPercentile.getPercentile(percentile) : C.TIME_UNSET;
}
@Override
public void reset() {
slidingPercentile.reset();
isEmpty = true;
}
@Override
public void onTransferInitializing(DataSpec dataSpec) {
// Remove to make sure insertion order is updated in case the key already exists.
initializedDataSpecs.remove(dataSpec);
initializedDataSpecs.put(dataSpec, Util.msToUs(clock.elapsedRealtime()));
}
@Override
public void onTransferStart(DataSpec dataSpec) {
@Nullable Long initializationStartUs = initializedDataSpecs.remove(dataSpec);
if (initializationStartUs == null) {
return;
}
slidingPercentile.addSample(
/* weight= */ 1,
/* value= */ (float) (Util.msToUs(clock.elapsedRealtime()) - initializationStartUs));
isEmpty = false;
}
private static class FixedSizeLinkedHashMap<K, V> extends LinkedHashMap<K, V> {
private final int maxSize;
public FixedSizeLinkedHashMap(int maxSize) {
this.maxSize = maxSize;
}
@Override
protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
return size() > maxSize;
}
}
}