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Java > Open Source Codes > org > jgroups > util > ThreadPool


1 // $Id: ThreadPool.java,v 1.8 2004/09/23 16:29:56 belaban Exp $
2
3 package org.jgroups.util;
4
5
6 import org.apache.commons.logging.Log;
7 import org.apache.commons.logging.LogFactory;
8
9
10 /**
11  * Maintains a set of ReusableThreads. When a thread is to be returned, all existing threads
12  * are checked: when one is available, it will be returned. Otherwise, a new thread is created
13  * and returned, unless the pool limit is reached, in which case <code>null</code> is returned.
14  * Creates threads only as needed, up to the MAX_NUM limit. However, does not shrink the pool
15  * when more threads become available than are used.
16  * todo: Shrink thread pool if threads are unused after some configurable time
17  *
18  * @author Bela Ban
19  */
20 public class ThreadPool {
21     int MAX_NUM=255;
22     int current_index=0; /// next available thread
23 ReusableThread[] pool=null;
24     boolean[] available_threads=null;
25     protected static final Log log=LogFactory.getLog(ThreadPool.class);
26
27
28
29     public ThreadPool(int max_num) {
30         MAX_NUM=max_num;
31         pool=new ReusableThread[MAX_NUM];
32         available_threads=new boolean[MAX_NUM];
33         for(int i=0; i < pool.length; i++) {
34             pool[i]=null;
35             available_threads[i]=true;
36         }
37         if(log.isDebugEnabled()) log.debug("created a pool of " + MAX_NUM + " threads");
38     }
39
40
41     public ReusableThread getThread() {
42         ReusableThread retval=null, tmp;
43
44         synchronized(pool) {
45             // check whether a previously created thread can be reused
46 for(int i=0; i < current_index; i++) {
47                 tmp=pool[i];
48                 if(tmp.available()) {
49                     return tmp;
50                 }
51             }
52
53             // else create a new thread and add it to the pool
54 if(current_index >= MAX_NUM) {
55                 if(log.isErrorEnabled()) log.error("could not create new thread because " +
56                         "pool's max size reached (" + MAX_NUM + ") !");
57                 return null;
58             }
59             else {
60                 retval=new ReusableThread();
61                 pool[current_index++]=retval;
62                 return retval;
63             }
64         }
65
66     }
67
68
69     public void destroy() {
70         deletePool();
71     }
72
73
74     public String JavaDoc toString() {
75         StringBuffer JavaDoc ret=new StringBuffer JavaDoc();
76
77         synchronized(pool) {
78             ret.append("ThreadPool: capacity=" + pool.length + ", index=" + current_index + '\n');
79             ret.append("Threads are:\n");
80             for(int i=0; i < current_index; i++)
81                 ret.append("[" + i + ": " + pool[i] + "]\n");
82         }
83         return ret.toString();
84     }
85
86
87     void deletePool() {
88         ReusableThread t;
89         synchronized(pool) {
90             for(int i=0; i < MAX_NUM; i++) {
91                 t=pool[i];
92                 if(t != null) {
93                     t.stop();
94                     pool[i]=null;
95                 }
96             }
97             current_index=0;
98         }
99     }
100
101
102 }
103
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