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Java > Open Source Codes > org > columba > ristretto > concurrency > Semaphore


1 /* ***** BEGIN LICENSE BLOCK *****
2  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
3  *
4  * The contents of this file are subject to the Mozilla Public License Version
5  * 1.1 (the "License"); you may not use this file except in compliance with
6  * the License. You may obtain a copy of the License at
7  * http://www.mozilla.org/MPL/
8  *
9  * Software distributed under the License is distributed on an "AS IS" basis,
10  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
11  * for the specific language governing rights and limitations under the
12  * License.
13  *
14  * The Original Code is Ristretto Mail API.
15  *
16  * The Initial Developers of the Original Code are
17  * Timo Stich and Frederik Dietz.
18  * Portions created by the Initial Developers are Copyright (C) 2004
19  * All Rights Reserved.
20  *
21  * Contributor(s):
22  *
23  * Alternatively, the contents of this file may be used under the terms of
24  * either the GNU General Public License Version 2 or later (the "GPL"), or
25  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
26  * in which case the provisions of the GPL or the LGPL are applicable instead
27  * of those above. If you wish to allow use of your version of this file only
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29  * use your version of this file under the terms of the MPL, indicate your
30  * decision by deleting the provisions above and replace them with the notice
31  * and other provisions required by the GPL or the LGPL. If you do not delete
32  * the provisions above, a recipient may use your version of this file under
33  * the terms of any one of the MPL, the GPL or the LGPL.
34  *
35  * ***** END LICENSE BLOCK ***** */
36 package org.columba.ristretto.concurrency;
37
38 /**
39  * Integer Semaphore implementation.
40  *
41  * @author Timo Stich <tstich@users.sourceforge.net>
42  */
43 public class Semaphore {
44     private int value;
45     
46     /**
47      * Constructs the Semaphore.
48      *
49      * @param value initial value
50      */
51     public Semaphore(int value) {
52         this.value = value;
53     }
54
55     /**
56      * Constructs the Semaphore.
57      */
58     public Semaphore() {
59         this(0);
60     }
61     
62     /**
63      * Acquires an amount from the semaphore. It there is
64      * not enough available the Thread is blocked.
65      *
66      * @param n the amount to acquire
67      */
68     public synchronized void acquire(int n) {
69         while( value < n) {
70             try {
71                 wait();
72             } catch (InterruptedException JavaDoc e) {
73                 e.printStackTrace();
74             }
75         }
76         
77         value -= n;
78     }
79     
80     /**
81      * Acquires one from the Semaphore.
82      * @see #acquire(int)
83      *
84      */
85     public void acquire() {
86         acquire(1);
87     }
88
89     /**
90      * Releases the specified amount from the Semaphore.
91      *
92      * @param n the amount to release.
93      */
94     public synchronized void release(int n) {
95         value += n;
96         
97         notify();
98     }
99 }
100
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