1 package org.apache.maven.plugin.surefire.booterclient;
2
3 /*
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 * KIND, either express or implied. See the License for the
18 * specific language governing permissions and limitations
19 * under the License.
20 */
21
22 import java.util.Queue;
23 import java.util.concurrent.ConcurrentLinkedQueue;
24 import java.util.concurrent.atomic.AtomicInteger;
25
26 /**
27 * A bucket from which fork numbers can be drawn. Any drawn number needs to be returned to the bucket, in order to keep
28 * the range of provided values delivered as small as possible.
29 *
30 * @author Andreas Gudian
31 */
32 public final class ForkNumberBucket
33 {
34 private static final ForkNumberBucket INSTANCE = new ForkNumberBucket();
35
36 private final Queue<Integer> qFree = new ConcurrentLinkedQueue<>();
37
38 private final AtomicInteger highWaterMark = new AtomicInteger( 1 );
39
40 /**
41 * Non-public constructor
42 */
43 private ForkNumberBucket()
44 {
45 }
46
47 /**
48 * @return a fork number that is not currently in use. The value must be returned to the bucket using
49 * {@link #returnNumber(int)}.
50 */
51 public static int drawNumber()
52 {
53 return getInstance().drawNumberInternal();
54 }
55
56 /**
57 * @param number the number to return to the bucket so that it can be reused.
58 */
59 public static void returnNumber( int number )
60 {
61 getInstance().returnNumberInternal( number );
62 }
63
64 /**
65 * @return a singleton instance
66 */
67 private static ForkNumberBucket getInstance()
68 {
69 return INSTANCE;
70 }
71
72 /**
73 * @return a fork number that is not currently in use. The value must be returned to the bucket using
74 * {@link #returnNumber(int)}.
75 */
76 private int drawNumberInternal()
77 {
78 Integer nextFree = qFree.poll();
79 return nextFree == null ? highWaterMark.getAndIncrement() : nextFree;
80 }
81
82 /**
83 * @return the highest number that has been drawn
84 */
85 private int getHighestDrawnNumber()
86 {
87 return highWaterMark.get() - 1;
88 }
89
90 /**
91 * @param number the number to return to the bucket so that it can be reused.
92 */
93 private void returnNumberInternal( int number )
94 {
95 qFree.add( number );
96 }
97 }