1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.lang3.concurrent;
18
19 import java.util.concurrent.atomic.AtomicLong;
20
21 /**
22 * A simple implementation of the <a
23 * href="https://martinfowler.com/bliki/CircuitBreaker.html">Circuit Breaker</a> pattern
24 * that opens if the requested increment amount is greater than a given threshold.
25 *
26 * <p>
27 * It contains an internal counter that starts in zero, and each call increments the counter by a given amount.
28 * If the threshold is zero, the circuit breaker will be in a permanent <em>open</em> state.
29 * </p>
30 *
31 * <p>
32 * An example of use case could be a memory circuit breaker.
33 * </p>
34 *
35 * <pre>
36 * long threshold = 10L;
37 * ThresholdCircuitBreaker breaker = new ThresholdCircuitBreaker(10L);
38 * ...
39 * public void handleRequest(Request request) {
40 * long memoryUsed = estimateMemoryUsage(request);
41 * if (breaker.incrementAndCheckState(memoryUsed)) {
42 * // actually handle this request
43 * } else {
44 * // do something else, e.g. send an error code
45 * }
46 * }
47 * </pre>
48 *
49 * <p>#Thread safe#</p>
50 * @since 3.5
51 */
52 public class ThresholdCircuitBreaker extends AbstractCircuitBreaker<Long> {
53 /**
54 * The initial value of the internal counter.
55 */
56 private static final long INITIAL_COUNT = 0L;
57
58 /**
59 * The threshold.
60 */
61 private final long threshold;
62
63 /**
64 * Controls the amount used.
65 */
66 private final AtomicLong used;
67
68 /**
69 * Creates a new instance of {@link ThresholdCircuitBreaker} and initializes the threshold.
70 *
71 * @param threshold the threshold.
72 */
73 public ThresholdCircuitBreaker(final long threshold) {
74 this.used = new AtomicLong(INITIAL_COUNT);
75 this.threshold = threshold;
76 }
77
78 /**
79 * {@inheritDoc}
80 */
81 @Override
82 public boolean checkState() {
83 return !isOpen();
84 }
85
86 /**
87 * {@inheritDoc}
88 *
89 * <p>Resets the internal counter back to its initial value (zero).</p>
90 */
91 @Override
92 public void close() {
93 super.close();
94 this.used.set(INITIAL_COUNT);
95 }
96
97 /**
98 * Gets the threshold.
99 *
100 * @return the threshold
101 */
102 public long getThreshold() {
103 return threshold;
104 }
105
106 /**
107 * {@inheritDoc}
108 *
109 * <p>If the threshold is zero, the circuit breaker will be in a permanent <em>open</em> state.</p>
110 */
111 @Override
112 public boolean incrementAndCheckState(final Long increment) {
113 if (threshold == 0) {
114 open();
115 }
116
117 final long used = this.used.addAndGet(increment);
118 if (used > threshold) {
119 open();
120 }
121
122 return checkState();
123 }
124
125 }