Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you 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 org.apache.cassandra.metrics; import java.io.Serializable; import java.util.List; import java.util.concurrent.ArrayBlockingQueue; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit; import org.apache.cassandra.concurrent.JMXEnabledThreadPoolExecutor; import org.apache.cassandra.concurrent.NamedThreadFactory; import org.apache.cassandra.net.MessagingService; import org.apache.cassandra.net.Verb; import org.apache.cassandra.utils.MonotonicClock; import com.google.common.annotations.VisibleForTesting; public abstract class Sampler<T> { public enum SamplerType { READS, WRITES, LOCAL_READ_TIME, WRITE_SIZE, CAS_CONTENTIONS } @VisibleForTesting MonotonicClock clock = MonotonicClock.approxTime; @VisibleForTesting static final ThreadPoolExecutor samplerExecutor = new JMXEnabledThreadPoolExecutor(1, 1, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(1000), new NamedThreadFactory("Sampler"), "internal"); static { samplerExecutor.setRejectedExecutionHandler((runnable, executor) -> { MessagingService.instance().metrics.recordSelfDroppedMessage(Verb._SAMPLE); }); } public void addSample(final T item, final int value) { if (isEnabled()) samplerExecutor.submit(() -> insert(item, value)); } protected abstract void insert(T item, long value); public abstract boolean isEnabled(); public abstract void beginSampling(int capacity, int durationMillis); public abstract List<Sample<T>> finishSampling(int count); public abstract String toString(T value); /** * Represents the ranked items collected during a sample period */ public static class Sample<S> implements Serializable { public final S value; public final long count; public final long error; public Sample(S value, long count, long error) { this.value = value; this.count = count; this.error = error; } @Override public String toString() { return "Sample [value=" + value + ", count=" + count + ", error=" + error + "]"; } } }