128 lines
3.4 KiB
Java
128 lines
3.4 KiB
Java
/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.commons.lang3.concurrent;
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import java.util.concurrent.atomic.AtomicLong;
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/**
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* <p>
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* A simple implementation of the <a
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* href="http://martinfowler.com/bliki/CircuitBreaker.html">Circuit Breaker</a> pattern
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* that opens if the requested increment amount is greater than a given threshold.
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* </p>
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*
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* <p>
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* It contains an internal counter that starts in zero, and each call increments the counter by a given amount.
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* If the threshold is zero, the circuit breaker will be in a permanent <em>open</em> state.
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* </p>
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*
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* <p>
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* An example of use case could be a memory circuit breaker.
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* </p>
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*
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* <pre>
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* long threshold = 10L;
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* ThresholdCircuitBreaker breaker = new ThresholdCircuitBreaker(10L);
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* ...
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* public void handleRequest(Request request) {
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* long memoryUsed = estimateMemoryUsage(request);
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* if (breaker.incrementAndCheckState(memoryUsed)) {
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* // actually handle this request
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* } else {
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* // do something else, e.g. send an error code
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* }
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* }
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* </pre>
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*
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* <p>#Thread safe#</p>
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* @since 3.5
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*/
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public class ThresholdCircuitBreaker extends AbstractCircuitBreaker<Long> {
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/**
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* The initial value of the internal counter.
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*/
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private static final long INITIAL_COUNT = 0L;
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/**
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* The threshold.
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*/
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private final long threshold;
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/**
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* Controls the amount used.
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*/
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private final AtomicLong used;
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/**
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* <p>Creates a new instance of {@code ThresholdCircuitBreaker} and initializes the threshold.</p>
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*
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* @param threshold the threshold.
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*/
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public ThresholdCircuitBreaker(final long threshold) {
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this.used = new AtomicLong(INITIAL_COUNT);
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this.threshold = threshold;
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}
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/**
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* Gets the threshold.
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*
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* @return the threshold
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*/
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public long getThreshold() {
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return threshold;
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}
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/**
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* {@inheritDoc}
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*/
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@Override
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public boolean checkState() {
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return isOpen();
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}
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/**
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* {@inheritDoc}
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*
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* <p>Resets the internal counter back to its initial value (zero).</p>
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*/
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@Override
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public void close() {
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super.close();
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this.used.set(INITIAL_COUNT);
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}
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/**
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* {@inheritDoc}
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*
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* <p>If the threshold is zero, the circuit breaker will be in a permanent <em>open</em> state.</p>
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*/
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@Override
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public boolean incrementAndCheckState(final Long increment) {
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if (threshold == 0) {
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open();
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}
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final long used = this.used.addAndGet(increment);
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if (used > threshold) {
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open();
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}
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return checkState();
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}
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}
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