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Apache Commons Lang, a package of Java utility classes for the classes that are in java.lang's hierarchy, or are considered to be so standard as to justify existence in java.lang. The code is tested using the latest revision of the JDK for supported LTS releases: 8, 11, 17 and 21 currently. See https://github.com/apache/commons-lang/blob/master/.github/workflows/maven.yml Please ensure your build environment is up-to-date and kindly report any build issues.

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/*
 * 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;

/**
 * 
 * A simple implementation of the Circuit Breaker pattern
 * that opens if the requested increment amount is greater than a given threshold.
 * 
 *
 * 
 * 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 open state.
 * 
 *
 * 
 * An example of use case could be a memory circuit breaker.
 * 
 *
 *  * 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
 *     }
 * }
 * 
 *
 * #Thread safe#
 * @since 3.5
 */
public class ThresholdCircuitBreaker extends AbstractCircuitBreaker {
    /**
     * 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;

    /**
     * Creates a new instance of {@code ThresholdCircuitBreaker} and initializes the threshold.
     *
     * @param threshold the threshold.
     */
    public ThresholdCircuitBreaker(final 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() {
        return isOpen();
    }

    /**
     * {@inheritDoc}
     *
     * Resets the internal counter back to its initial value (zero).
     */
    @Override
    public void close() {
        super.close();
        this.used.set(INITIAL_COUNT);
    }

    /**
     * {@inheritDoc}
     *
     * If the threshold is zero, the circuit breaker will be in a permanent open state.
     */
    @Override
    public boolean incrementAndCheckState(final Long increment) {
        if (threshold == 0) {
            open();
        }

        final long used = this.used.addAndGet(increment);
        if (used > threshold) {
            open();
        }

        return checkState();
    }

}