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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.

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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(); } }




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