| /* |
| * 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</em> 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#</p> |
| * @since 3.5 |
| */ |
| public class ThresholdCircuitBreaker extends AbstractCircuitBreaker<Long> { |
| /** |
| * The initial value of the internal counter. |
| */ |
| private static final 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.</p> |
| * |
| * @param threshold the threshold. |
| */ |
| public ThresholdCircuitBreaker(final long threshold) { |
| 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() { |
| return isOpen(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * <p>Resets the internal counter back to its initial value (zero).</p> |
| */ |
| @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 <em>open</em> state.</p> |
| */ |
| @Override |
| public boolean incrementAndCheckState(final Long increment) { |
| if (threshold == 0) { |
| open(); |
| } |
| |
| final long used = this.used.addAndGet(increment); |
| if (used > threshold) { |
| open(); |
| } |
| |
| return checkState(); |
| } |
| |
| } |