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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 <a
+ * href="https://martinfowler.com/bliki/CircuitBreaker.html">Circuit Breaker</a> pattern
+ * that opens if the requested increment amount is greater than a given threshold.
+ *
+ * <p>
+ * 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 <em>open</em> state.
+ * </p>
+ *
+ * <p>
+ * An example of use case could be a memory circuit breaker.
+ * </p>
+ *
+ * <pre>
+ * 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
+ * }
+ * }
+ * </pre>
+ *
+ * <p>#Thread safe#</p>
+ * @since 3.5
+ */
+public class ThresholdCircuitBreaker extends AbstractCircuitBreaker<Long> {
+ /**
+ * 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 {@link ThresholdCircuitBreaker} and initializes the threshold.
+ *
+ * @param threshold the threshold.
+ */
+ public ThresholdCircuitBreaker(final long threshold) {
+ 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}
+ *
+ * <p>Resets the internal counter back to its initial value (zero).</p>
+ */
+ @Override
+ public void close() {
+ super.close();
+ this.used.set(INITIAL_COUNT);
+ }
+
+ /**
+ * {@inheritDoc}
+ *
+ * <p>If the threshold is zero, the circuit breaker will be in a permanent <em>open</em> state.</p>
+ */
+ @Override
+ public boolean incrementAndCheckState(final Long increment) {
+ if (threshold == 0) {
+ open();
+ }
+
+ final long used = this.used.addAndGet(increment);
+ if (used > threshold) {
+ open();
+ }
+
+ return checkState();
+ }
+
+}