001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.lang3.concurrent;
018
019import java.util.concurrent.atomic.AtomicLong;
020
021/**
022 * <p>
023 * A simple implementation of the <a
024 * href="http://martinfowler.com/bliki/CircuitBreaker.html">Circuit Breaker</a> pattern
025 * that opens if the requested increment amount is greater than a given threshold.
026 * </p>
027 *
028 * <p>
029 * It contains an internal counter that starts in zero, and each call increments the counter by a given amount.
030 * If the threshold is zero, the circuit breaker will be in a permanent <em>open</em> state.
031 * </p>
032 *
033 * <p>
034 * An example of use case could be a memory circuit breaker.
035 * </p>
036 *
037 * <pre>
038 * long threshold = 10L;
039 * ThresholdCircuitBreaker breaker = new ThresholdCircuitBreaker(10L);
040 * ...
041 * public void handleRequest(Request request) {
042 *     long memoryUsed = estimateMemoryUsage(request);
043 *     if (breaker.incrementAndCheckState(memoryUsed)) {
044 *         // actually handle this request
045 *     } else {
046 *         // do something else, e.g. send an error code
047 *     }
048 * }
049 * </pre>
050 *
051 * <p>#Thread safe#</p>
052 * @since 3.5
053 */
054public class ThresholdCircuitBreaker extends AbstractCircuitBreaker<Long> {
055    /**
056     * The initial value of the internal counter.
057     */
058    private static final long INITIAL_COUNT = 0L;
059
060    /**
061     * The threshold.
062     */
063    private final long threshold;
064
065    /**
066     * Controls the amount used.
067     */
068    private final AtomicLong used;
069
070    /**
071     * <p>Creates a new instance of {@code ThresholdCircuitBreaker} and initializes the threshold.</p>
072     *
073     * @param threshold the threshold.
074     */
075    public ThresholdCircuitBreaker(final long threshold) {
076        this.used = new AtomicLong(INITIAL_COUNT);
077        this.threshold = threshold;
078    }
079
080    /**
081     * Gets the threshold.
082     *
083     * @return the threshold
084     */
085    public long getThreshold() {
086        return threshold;
087    }
088
089    /**
090     * {@inheritDoc}
091     */
092    @Override
093    public boolean checkState() {
094        return isOpen();
095    }
096
097    /**
098     * {@inheritDoc}
099     *
100     * <p>Resets the internal counter back to its initial value (zero).</p>
101     */
102    @Override
103    public void close() {
104        super.close();
105        this.used.set(INITIAL_COUNT);
106    }
107
108    /**
109     * {@inheritDoc}
110     *
111     * <p>If the threshold is zero, the circuit breaker will be in a permanent <em>open</em> state.</p>
112     */
113    @Override
114    public boolean incrementAndCheckState(final Long increment) {
115        if (threshold == 0) {
116            open();
117        }
118
119        final long used = this.used.addAndGet(increment);
120        if (used > threshold) {
121            open();
122        }
123
124        return checkState();
125    }
126
127}