    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 * A simple implementation of the <a
    023 * href="https://martinfowler.com/bliki/CircuitBreaker.html">Circuit Breaker</a> pattern
    024 * that opens if the requested increment amount is greater than a given threshold.
    025 *
    026 * <p>
    027 * It contains an internal counter that starts in zero, and each call increments the counter by a given amount.
    028 * If the threshold is zero, the circuit breaker will be in a permanent <em>open</em> state.
    029 * </p>
    030 *
    031 * <p>
    032 * An example of use case could be a memory circuit breaker.
    033 * </p>
    034 *
    035 * <pre>
    036 * long threshold = 10L;
    037 * ThresholdCircuitBreaker breaker = new ThresholdCircuitBreaker(10L);
    038 * ...
    039 * public void handleRequest(Request request) {
    040 *     long memoryUsed = estimateMemoryUsage(request);
    041 *     if (breaker.incrementAndCheckState(memoryUsed)) {
    042 *         // actually handle this request
    043 *     } else {
    044 *         // do something else, e.g. send an error code
    045 *     }
    046 * }
    047 * </pre>
    048 *
    049 * <p>#Thread safe#</p>
    050 * @since 3.5
    051 */
    052public class ThresholdCircuitBreaker extends AbstractCircuitBreaker<Long> {
    053    /**
    054     * The initial value of the internal counter.
    055     */
    056    private static final long INITIAL_COUNT = 0L;
    057
    058    /**
    059     * The threshold.
    060     */
    061    private final long threshold;
    062
    063    /**
    064     * Controls the amount used.
    065     */
    066    private final AtomicLong used;
    067
    068    /**
    069     * Creates a new instance of {@link ThresholdCircuitBreaker} and initializes the threshold.
    070     *
    071     * @param threshold the threshold.
    072     */
    073    public ThresholdCircuitBreaker(final long threshold) {
    074        this.used = new AtomicLong(INITIAL_COUNT);
    075        this.threshold = threshold;
    076    }
    077
    078    /**
    079     * {@inheritDoc}
    080     */
    081    @Override
    082    public boolean checkState() {
    083        return !isOpen();
    084    }
    085
    086    /**
    087     * {@inheritDoc}
    088     *
    089     * <p>Resets the internal counter back to its initial value (zero).</p>
    090     */
    091    @Override
    092    public void close() {
    093        super.close();
    094        this.used.set(INITIAL_COUNT);
    095    }
    096
    097    /**
    098     * Gets the threshold.
    099     *
    100     * @return the threshold
    101     */
    102    public long getThreshold() {
    103        return threshold;
    104    }
    105
    106    /**
    107     * {@inheritDoc}
    108     *
    109     * <p>If the threshold is zero, the circuit breaker will be in a permanent <em>open</em> state.</p>
    110     */
    111    @Override
    112    public boolean incrementAndCheckState(final Long increment) {
    113        if (threshold == 0) {
    114            open();
    115        }
    116
    117        final long used = this.used.addAndGet(increment);
    118        if (used > threshold) {
    119            open();
    120        }
    121
    122        return checkState();
    123    }
    124
    125}