1 /**
2 * Copyright 2008 Atlassian Pty Ltd
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.atlassian.util.concurrent;
18
19 import java.util.concurrent.atomic.AtomicInteger;
20
21 /**
22 * Simple Latch-like structure where threads jump in a queue and are let off rally-style, one after
23 * the other.
24 */
25 interface LatchQueue {
26 /**
27 * await until a {@link #release()} is called
28 */
29 void await();
30
31 /**
32 * cause any threads backed up in {@link #await()} to go
33 */
34 void release();
35
36 /**
37 * How many threads are waiting.
38 *
39 * @return the number of threads waiting.
40 */
41 int size();
42
43 class SinglePass implements LatchQueue {
44 private final BooleanLatch latch = new BooleanLatch();
45 private final AtomicInteger count = new AtomicInteger();
46
47 /**
48 * Construct a new SinglePass LatchQueue, optionally with the first call to not wait by
49 * releasing the latch.
50 *
51 * @param prep if you want the first call to await to get a latch.
52 */
53 SinglePass(final boolean prep) {
54 if (prep) {
55 latch.release();
56 }
57 }
58
59 public void await() {
60 try {
61 count.incrementAndGet();
62 latch.await();
63 }
64 catch (final InterruptedException e) {
65 throw new RuntimeInterruptedException(e);
66 }
67 finally {
68 count.decrementAndGet();
69 }
70 }
71
72 public void release() {
73 latch.release();
74 }
75
76 public int size() {
77 return count.get();
78 }
79 }
80 }