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With inspiration from other libraries
/*
* 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();
}
}