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Java example source code file (ThresholdCircuitBreaker.java)

This example Java source code file (ThresholdCircuitBreaker.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

abstractcircuitbreaker, atomiclong, circuitbreakingexception, initial_count, override, thresholdcircuitbreaker

The ThresholdCircuitBreaker.java Java example source code

/*
 * 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.commons.lang3.concurrent;

import java.util.concurrent.atomic.AtomicLong;

/**
 * <p>
 * A simple implementation of the <a
 * href="http://martinfowler.com/bliki/CircuitBreaker.html">Circuit Breaker</a> pattern
 * that opens if the requested increment amount is greater than a given threshold.
 * </p>
 *
 * <p>
 * It contains an internal counter that starts in zero, and each call increments the counter by a given amount.
 * If the threshold is zero, the circuit breaker will be in a permanent <em>open state.
 * </p>
 *
 * <p>
 * An example of use case could be a memory circuit breaker.
 * </p>
 *
 * <pre>
 * long threshold = 10L;
 * ThresholdCircuitBreaker breaker = new ThresholdCircuitBreaker(10L);
 * ...
 * public void handleRequest(Request request) {
 *     long memoryUsed = estimateMemoryUsage(request);
 *     if (breaker.incrementAndCheckState(memoryUsed)) {
 *         // actually handle this request
 *     } else {
 *         // do something else, e.g. send an error code
 *     }
 * }
 * </pre>
 *
 * <p>#Thread safe#

* @since 3.5 */ public class ThresholdCircuitBreaker extends AbstractCircuitBreaker<Long> { /** * The initial value of the internal counter. */ private final static long INITIAL_COUNT = 0L; /** * The threshold. */ private final long threshold; /** * Controls the amount used. */ private final AtomicLong used; /** * <p>Creates a new instance of {@code ThresholdCircuitBreaker} and initializes the threshold.

* * @param threshold the threshold. */ public ThresholdCircuitBreaker(long threshold) { super(); this.used = new AtomicLong(INITIAL_COUNT); this.threshold = threshold; } /** * Gets the threshold. * * @return the threshold */ public long getThreshold() { return threshold; } /** * {@inheritDoc} */ @Override public boolean checkState() throws CircuitBreakingException { return isOpen(); } /** * {@inheritDoc} * * <p>Resets the internal counter back to its initial value (zero).

*/ @Override public void close() { super.close(); this.used.set(INITIAL_COUNT); } /** * {@inheritDoc} * * <p>If the threshold is zero, the circuit breaker will be in a permanent open state.

*/ @Override public boolean incrementAndCheckState(Long increment) throws CircuitBreakingException { if (threshold == 0) { open(); } long used = this.used.addAndGet(increment); if (used > threshold) { open(); } return checkState(); } }

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