1 | /* |
2 | * @(#) $Id: BaseThreadPool.java 327113 2005-10-21 06:59:15Z trustin $ |
3 | * |
4 | * Copyright 2004 The Apache Software Foundation |
5 | * |
6 | * Licensed under the Apache License, Version 2.0 (the "License"); |
7 | * you may not use this file except in compliance with the License. |
8 | * You may obtain a copy of the License at |
9 | * |
10 | * http://www.apache.org/licenses/LICENSE-2.0 |
11 | * |
12 | * Unless required by applicable law or agreed to in writing, software |
13 | * distributed under the License is distributed on an "AS IS" BASIS, |
14 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
15 | * See the License for the specific language governing permissions and |
16 | * limitations under the License. |
17 | * |
18 | */ |
19 | package org.apache.mina.util; |
20 | |
21 | import java.util.HashSet; |
22 | import java.util.IdentityHashMap; |
23 | import java.util.Map; |
24 | import java.util.Set; |
25 | |
26 | import org.apache.mina.common.Session; |
27 | |
28 | /** |
29 | * A base implementation of Thread-pooling filters. |
30 | * This filter forwards events to its thread pool. This is an implementation of |
31 | * <a href="http://deuce.doc.wustl.edu/doc/pspdfs/lf.pdf">Leader/Followers |
32 | * thread pool</a> by Douglas C. Schmidt et al. |
33 | * |
34 | * @author The Apache Directory Project (dev@directory.apache.org) |
35 | * @version $Rev: 327113 $, $Date: 2005-10-21 15:59:15 +0900 $ |
36 | */ |
37 | public abstract class BaseThreadPool implements ThreadPool |
38 | { |
39 | /** |
40 | * Default maximum size of thread pool (2G). |
41 | */ |
42 | public static final int DEFAULT_MAXIMUM_POOL_SIZE = Integer.MAX_VALUE; |
43 | |
44 | /** |
45 | * Default keep-alive time of thread pool (1 min). |
46 | */ |
47 | public static final int DEFAULT_KEEP_ALIVE_TIME = 60 * 1000; |
48 | |
49 | /** |
50 | * A queue which contains {@link Integer}s which represents reusable |
51 | * thread IDs. {@link Worker} first checks this queue and then |
52 | * uses {@link #threadId} when no reusable thread ID is available. |
53 | */ |
54 | private static final Queue threadIdReuseQueue = new Queue(); |
55 | private static int threadId = 0; |
56 | |
57 | private static int acquireThreadId() |
58 | { |
59 | synchronized( threadIdReuseQueue ) |
60 | { |
61 | Integer id = ( Integer ) threadIdReuseQueue.pop(); |
62 | if( id == null ) |
63 | { |
64 | return ++ threadId; |
65 | } |
66 | else |
67 | { |
68 | return id.intValue(); |
69 | } |
70 | } |
71 | } |
72 | |
73 | private static void releaseThreadId( int id ) |
74 | { |
75 | synchronized( threadIdReuseQueue ) |
76 | { |
77 | threadIdReuseQueue.push( new Integer( id ) ); |
78 | } |
79 | } |
80 | |
81 | private final String threadNamePrefix; |
82 | private final Map buffers = new IdentityHashMap(); |
83 | private final Stack followers = new Stack(); |
84 | private final BlockingQueue unfetchedSessionBuffers = new BlockingQueue(); |
85 | private final Set allSessionBuffers = new HashSet(); |
86 | |
87 | private Worker leader; |
88 | |
89 | private int maximumPoolSize = DEFAULT_MAXIMUM_POOL_SIZE; |
90 | private int keepAliveTime = DEFAULT_KEEP_ALIVE_TIME; |
91 | |
92 | private boolean started; |
93 | private boolean shuttingDown; |
94 | |
95 | private int poolSize; |
96 | private final Object poolSizeLock = new Object(); |
97 | |
98 | /** |
99 | * Creates a new instance with default thread pool settings. |
100 | * You'll have to invoke {@link #start()} method to start threads actually. |
101 | * |
102 | * @param threadNamePrefix the prefix of the thread names this pool will create. |
103 | */ |
104 | public BaseThreadPool( String threadNamePrefix ) |
105 | { |
106 | if( threadNamePrefix == null ) |
107 | { |
108 | throw new NullPointerException( "threadNamePrefix" ); |
109 | } |
110 | threadNamePrefix = threadNamePrefix.trim(); |
111 | if( threadNamePrefix.length() == 0 ) |
112 | { |
113 | throw new IllegalArgumentException( "threadNamePrefix is empty." ); |
114 | } |
115 | this.threadNamePrefix = threadNamePrefix; |
116 | } |
117 | |
118 | public String getThreadNamePrefix() |
119 | { |
120 | return threadNamePrefix; |
121 | } |
122 | |
123 | public int getPoolSize() |
124 | { |
125 | synchronized( poolSizeLock ) |
126 | { |
127 | return poolSize; |
128 | } |
129 | } |
130 | |
131 | public int getMaximumPoolSize() |
132 | { |
133 | return maximumPoolSize; |
134 | } |
135 | |
136 | public int getKeepAliveTime() |
137 | { |
138 | return keepAliveTime; |
139 | } |
140 | |
141 | public void setMaximumPoolSize( int maximumPoolSize ) |
142 | { |
143 | if( maximumPoolSize <= 0 ) |
144 | throw new IllegalArgumentException(); |
145 | this.maximumPoolSize = maximumPoolSize; |
146 | } |
147 | |
148 | public void setKeepAliveTime( int keepAliveTime ) |
149 | { |
150 | this.keepAliveTime = keepAliveTime; |
151 | } |
152 | |
153 | public synchronized void start() |
154 | { |
155 | if( started ) |
156 | return; |
157 | |
158 | shuttingDown = false; |
159 | |
160 | leader = new Worker(); |
161 | leader.start(); |
162 | leader.lead(); |
163 | |
164 | started = true; |
165 | } |
166 | |
167 | public synchronized void stop() |
168 | { |
169 | if( !started ) |
170 | return; |
171 | |
172 | shuttingDown = true; |
173 | Worker lastLeader = null; |
174 | for( ;; ) |
175 | { |
176 | Worker leader = this.leader; |
177 | if( lastLeader == leader ) |
178 | break; |
179 | |
180 | while( leader.isAlive() ) |
181 | { |
182 | leader.interrupt(); |
183 | try |
184 | { |
185 | leader.join(); |
186 | } |
187 | catch( InterruptedException e ) |
188 | { |
189 | } |
190 | } |
191 | |
192 | lastLeader = leader; |
193 | } |
194 | |
195 | started = false; |
196 | } |
197 | |
198 | private void increasePoolSize() |
199 | { |
200 | synchronized( poolSizeLock ) |
201 | { |
202 | poolSize++; |
203 | } |
204 | } |
205 | |
206 | private void decreasePoolSize() |
207 | { |
208 | synchronized( poolSizeLock ) |
209 | { |
210 | poolSize--; |
211 | } |
212 | } |
213 | |
214 | protected void fireEvent( Object nextFilter, Session session, |
215 | EventType type, Object data ) |
216 | { |
217 | final BlockingQueue unfetchedSessionBuffers = this.unfetchedSessionBuffers; |
218 | final Set allSessionBuffers = this.allSessionBuffers; |
219 | final Event event = new Event( type, nextFilter, data ); |
220 | |
221 | synchronized( unfetchedSessionBuffers ) |
222 | { |
223 | final SessionBuffer buf = getSessionBuffer( session ); |
224 | final Queue eventQueue = buf.eventQueue; |
225 | |
226 | synchronized( buf ) |
227 | { |
228 | eventQueue.push( event ); |
229 | } |
230 | |
231 | if( !allSessionBuffers.contains( buf ) ) |
232 | { |
233 | allSessionBuffers.add( buf ); |
234 | unfetchedSessionBuffers.push( buf ); |
235 | } |
236 | } |
237 | } |
238 | |
239 | /** |
240 | * Implement this method to forward events to <tt>nextFilter</tt>. |
241 | */ |
242 | protected abstract void processEvent( Object nextFilter, Session session, |
243 | EventType type, Object data ); |
244 | |
245 | |
246 | /** |
247 | * Implement this method to fetch (or pop) a {@link SessionBuffer} from |
248 | * the given <tt>unfetchedSessionBuffers</tt>. The default implementation |
249 | * simply pops the buffer from it. You could prioritize the fetch order. |
250 | * |
251 | * @return A non-null {@link SessionBuffer} |
252 | */ |
253 | protected SessionBuffer fetchSessionBuffer( Queue unfetchedSessionBuffers ) |
254 | { |
255 | return ( SessionBuffer ) unfetchedSessionBuffers.pop(); |
256 | } |
257 | |
258 | private SessionBuffer getSessionBuffer( Session session ) |
259 | { |
260 | final Map buffers = this.buffers; |
261 | SessionBuffer buf = ( SessionBuffer ) buffers.get( session ); |
262 | if( buf == null ) |
263 | { |
264 | synchronized( buffers ) |
265 | { |
266 | buf = ( SessionBuffer ) buffers.get( session ); |
267 | if( buf == null ) |
268 | { |
269 | buf = new SessionBuffer( session ); |
270 | buffers.put( session, buf ); |
271 | } |
272 | } |
273 | } |
274 | return buf; |
275 | } |
276 | |
277 | private void removeSessionBuffer( SessionBuffer buf ) |
278 | { |
279 | final Map buffers = this.buffers; |
280 | final Session session = buf.session; |
281 | synchronized( buffers ) |
282 | { |
283 | buffers.remove( session ); |
284 | } |
285 | } |
286 | |
287 | protected static class SessionBuffer |
288 | { |
289 | private final Session session; |
290 | |
291 | private final Queue eventQueue = new Queue(); |
292 | |
293 | private SessionBuffer( Session session ) |
294 | { |
295 | this.session = session; |
296 | } |
297 | |
298 | public Session getSession() |
299 | { |
300 | return session; |
301 | } |
302 | |
303 | public Queue getEventQueue() |
304 | { |
305 | return eventQueue; |
306 | } |
307 | } |
308 | |
309 | private class Worker extends Thread |
310 | { |
311 | private final int id; |
312 | private final Object promotionLock = new Object(); |
313 | private boolean dead; |
314 | |
315 | private Worker() |
316 | { |
317 | int id = acquireThreadId(); |
318 | this.id = id; |
319 | this.setName( threadNamePrefix + '-' + id ); |
320 | increasePoolSize(); |
321 | } |
322 | |
323 | public boolean lead() |
324 | { |
325 | final Object promotionLock = this.promotionLock; |
326 | synchronized( promotionLock ) |
327 | { |
328 | if( dead ) |
329 | { |
330 | return false; |
331 | } |
332 | |
333 | leader = this; |
334 | promotionLock.notify(); |
335 | } |
336 | |
337 | return true; |
338 | } |
339 | |
340 | public void run() |
341 | { |
342 | for( ;; ) |
343 | { |
344 | if( !waitForPromotion() ) |
345 | break; |
346 | |
347 | SessionBuffer buf = fetchBuffer(); |
348 | giveUpLead(); |
349 | |
350 | if( buf == null ) |
351 | { |
352 | break; |
353 | } |
354 | |
355 | processEvents( buf ); |
356 | follow(); |
357 | releaseBuffer( buf ); |
358 | } |
359 | |
360 | decreasePoolSize(); |
361 | releaseThreadId( id ); |
362 | } |
363 | |
364 | private SessionBuffer fetchBuffer() |
365 | { |
366 | BlockingQueue unfetchedSessionBuffers = BaseThreadPool.this.unfetchedSessionBuffers; |
367 | synchronized( unfetchedSessionBuffers ) |
368 | { |
369 | for( ;; ) |
370 | { |
371 | if( shuttingDown ) |
372 | { |
373 | return null; |
374 | } |
375 | |
376 | try |
377 | { |
378 | unfetchedSessionBuffers.waitForNewItem(); |
379 | } |
380 | catch( InterruptedException e ) |
381 | { |
382 | if( shuttingDown ) |
383 | { |
384 | return null; |
385 | } |
386 | else |
387 | { |
388 | continue; |
389 | } |
390 | } |
391 | |
392 | return BaseThreadPool.this.fetchSessionBuffer( unfetchedSessionBuffers ); |
393 | } |
394 | } |
395 | } |
396 | |
397 | private void processEvents( SessionBuffer buf ) |
398 | { |
399 | final Session session = buf.session; |
400 | final Queue eventQueue = buf.eventQueue; |
401 | for( ;; ) |
402 | { |
403 | Event event; |
404 | synchronized( buf ) |
405 | { |
406 | event = ( Event ) eventQueue.pop(); |
407 | if( event == null ) |
408 | break; |
409 | } |
410 | processEvent( event.getNextFilter(), session, |
411 | event.getType(), event.getData() ); |
412 | } |
413 | } |
414 | |
415 | private void follow() |
416 | { |
417 | final Object promotionLock = this.promotionLock; |
418 | final Stack followers = BaseThreadPool.this.followers; |
419 | synchronized( promotionLock ) |
420 | { |
421 | if( this != leader ) |
422 | { |
423 | synchronized( followers ) |
424 | { |
425 | followers.push( this ); |
426 | } |
427 | } |
428 | } |
429 | } |
430 | |
431 | private void releaseBuffer( SessionBuffer buf ) |
432 | { |
433 | final BlockingQueue unfetchedSessionBuffers = BaseThreadPool.this.unfetchedSessionBuffers; |
434 | final Set allSessionBuffers = BaseThreadPool.this.allSessionBuffers; |
435 | final Queue eventQueue = buf.eventQueue; |
436 | |
437 | synchronized( unfetchedSessionBuffers ) |
438 | { |
439 | if( eventQueue.isEmpty() ) |
440 | { |
441 | allSessionBuffers.remove( buf ); |
442 | removeSessionBuffer( buf ); |
443 | } |
444 | else |
445 | { |
446 | unfetchedSessionBuffers.push( buf ); |
447 | } |
448 | } |
449 | } |
450 | |
451 | private boolean waitForPromotion() |
452 | { |
453 | final Object promotionLock = this.promotionLock; |
454 | |
455 | final long startTime = System.currentTimeMillis(); |
456 | long currentTime = startTime; |
457 | |
458 | synchronized( promotionLock ) |
459 | { |
460 | while( this != leader ) |
461 | { |
462 | // Calculate remaining keep-alive time |
463 | int keepAliveTime = getKeepAliveTime(); |
464 | if( keepAliveTime > 0 ) |
465 | { |
466 | keepAliveTime -= ( currentTime - startTime ); |
467 | } |
468 | else |
469 | { |
470 | keepAliveTime = Integer.MAX_VALUE; |
471 | } |
472 | |
473 | // Break the loop if there's no remaining keep-alive time. |
474 | if( keepAliveTime <= 0 ) |
475 | { |
476 | break; |
477 | } |
478 | |
479 | // Wait for promotion |
480 | try |
481 | { |
482 | promotionLock.wait( keepAliveTime ); |
483 | } |
484 | catch( InterruptedException e ) |
485 | { |
486 | if( shuttingDown ) |
487 | { |
488 | break; |
489 | } |
490 | } |
491 | |
492 | // Update currentTime for the next iteration |
493 | currentTime = System.currentTimeMillis(); |
494 | } |
495 | |
496 | boolean timeToLead = this == leader && !shuttingDown; |
497 | |
498 | if( !timeToLead ) |
499 | { |
500 | // time to die |
501 | synchronized( followers ) |
502 | { |
503 | followers.remove( this ); |
504 | } |
505 | |
506 | // Mark as dead explicitly when we've got promotionLock. |
507 | dead = true; |
508 | } |
509 | |
510 | return timeToLead; |
511 | } |
512 | } |
513 | |
514 | private void giveUpLead() |
515 | { |
516 | final Stack followers = BaseThreadPool.this.followers; |
517 | Worker worker; |
518 | do |
519 | { |
520 | synchronized( followers ) |
521 | { |
522 | worker = ( Worker ) followers.pop(); |
523 | } |
524 | |
525 | if( worker == null ) |
526 | { |
527 | // Increase the number of threads if we |
528 | // are not shutting down and we can increase the number. |
529 | if( !shuttingDown |
530 | && getPoolSize() < getMaximumPoolSize() ) |
531 | { |
532 | worker = new Worker(); |
533 | worker.lead(); |
534 | worker.start(); |
535 | } |
536 | |
537 | // This loop should end because: |
538 | // 1) lead() is called already, |
539 | // 2) or it is shutting down and there's no more threads left. |
540 | break; |
541 | } |
542 | } |
543 | while( !worker.lead() ); |
544 | } |
545 | } |
546 | } |