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1   /*
2    * Copyright 2009 Red Hat, Inc.
3    *
4    * Red Hat licenses this file to you under the Apache License, version 2.0
5    * (the "License"); you may not use this file except in compliance with the
6    * License.  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, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package org.jboss.netty.channel.socket.nio;
17  
18  import static org.jboss.netty.channel.Channels.*;
19  
20  import java.io.IOException;
21  import java.net.SocketAddress;
22  import java.nio.ByteBuffer;
23  import java.nio.channels.AsynchronousCloseException;
24  import java.nio.channels.CancelledKeyException;
25  import java.nio.channels.ClosedChannelException;
26  import java.nio.channels.DatagramChannel;
27  import java.nio.channels.NotYetConnectedException;
28  import java.nio.channels.SelectionKey;
29  import java.nio.channels.Selector;
30  import java.util.Iterator;
31  import java.util.Queue;
32  import java.util.Set;
33  import java.util.concurrent.Executor;
34  import java.util.concurrent.ExecutorService;
35  import java.util.concurrent.atomic.AtomicBoolean;
36  import java.util.concurrent.locks.ReadWriteLock;
37  import java.util.concurrent.locks.ReentrantReadWriteLock;
38  
39  import org.jboss.netty.buffer.ChannelBufferFactory;
40  import org.jboss.netty.channel.Channel;
41  import org.jboss.netty.channel.ChannelException;
42  import org.jboss.netty.channel.ChannelFuture;
43  import org.jboss.netty.channel.MessageEvent;
44  import org.jboss.netty.channel.ReceiveBufferSizePredictor;
45  import org.jboss.netty.channel.socket.nio.SocketSendBufferPool.SendBuffer;
46  import org.jboss.netty.logging.InternalLogger;
47  import org.jboss.netty.logging.InternalLoggerFactory;
48  import org.jboss.netty.util.ThreadRenamingRunnable;
49  import org.jboss.netty.util.internal.LinkedTransferQueue;
50  
51  /**
52   * A class responsible for registering channels with {@link Selector}.
53   * It also implements the {@link Selector} loop.
54   *
55   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
56   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
57   * @author Daniel Bevenius (dbevenius@jboss.com)
58   *
59   * @version $Rev: 2376 $, $Date: 2010-10-25 03:24:20 +0900 (Mon, 25 Oct 2010) $
60   */
61  class NioDatagramWorker implements Runnable {
62      /**
63       * Internal Netty logger.
64       */
65      private static final InternalLogger logger = InternalLoggerFactory
66              .getInstance(NioDatagramWorker.class);
67  
68      /**
69       * This id of this worker.
70       */
71      private final int id;
72  
73      /**
74       * This id of the NioDatagramPipelineSink.
75       */
76      private final int bossId;
77  
78      /**
79       * Executor used to execute {@link Runnable}s such as
80       * {@link ChannelRegistionTask}.
81       */
82      private final Executor executor;
83  
84      /**
85       * Boolean to indicate if this worker has been started.
86       */
87      private boolean started;
88  
89      /**
90       * If this worker has been started thread will be a reference to the thread
91       * used when starting. i.e. the current thread when the run method is executed.
92       */
93      private volatile Thread thread;
94  
95      /**
96       * The NIO {@link Selector}.
97       */
98      volatile Selector selector;
99  
100     /**
101      * Boolean that controls determines if a blocked Selector.select should
102      * break out of its selection process. In our case we use a timeone for
103      * the select method and the select method will block for that time unless
104      * waken up.
105      */
106     private final AtomicBoolean wakenUp = new AtomicBoolean();
107 
108     /**
109      * Lock for this workers Selector.
110      */
111     private final ReadWriteLock selectorGuard = new ReentrantReadWriteLock();
112 
113     /**
114      * Monitor object used to synchronize selector open/close.
115      */
116     private final Object startStopLock = new Object();
117 
118     /**
119      * Queue of {@link ChannelRegistionTask}s
120      */
121     private final Queue<Runnable> registerTaskQueue = new LinkedTransferQueue<Runnable>();
122 
123     /**
124      * Queue of WriteTasks
125      */
126     private final Queue<Runnable> writeTaskQueue = new LinkedTransferQueue<Runnable>();
127 
128     private volatile int cancelledKeys; // should use AtomicInteger but we just need approximation
129 
130     private final SocketSendBufferPool sendBufferPool = new SocketSendBufferPool();
131 
132     /**
133      * Sole constructor.
134      *
135      * @param bossId This id of the NioDatagramPipelineSink
136      * @param id The id of this worker
137      * @param executor the {@link Executor} used to execute {@link Runnable}s
138      *                 such as {@link ChannelRegistionTask}
139      */
140     NioDatagramWorker(final int bossId, final int id, final Executor executor) {
141         this.bossId = bossId;
142         this.id = id;
143         this.executor = executor;
144     }
145 
146     /**
147      * Registers the passed-in channel with a selector.
148      *
149      * @param channel the channel to register
150      * @param future  the {@link ChannelFuture} that has to be notified on
151      *                completion
152      */
153     void register(final NioDatagramChannel channel, final ChannelFuture future) {
154         final Runnable channelRegTask = new ChannelRegistionTask(channel,
155                 future);
156         Selector selector;
157 
158         synchronized (startStopLock) {
159             if (!started) {
160                 // Open a selector if this worker didn't start yet.
161                 try {
162                     this.selector = selector = Selector.open();
163                 } catch (final Throwable t) {
164                     throw new ChannelException("Failed to create a selector.",
165                             t);
166                 }
167 
168                 boolean success = false;
169                 try {
170                     // Start the main selector loop. See run() for details.
171                     executor.execute(new ThreadRenamingRunnable(this,
172                             "New I/O datagram worker #" + bossId + "'-'" + id));
173                     success = true;
174                 } finally {
175                     if (!success) {
176                         try {
177                             // Release the Selector if the execution fails.
178                             selector.close();
179                         } catch (final Throwable t) {
180                             logger.warn("Failed to close a selector.", t);
181                         }
182                         this.selector = selector = null;
183                         // The method will return to the caller at this point.
184                     }
185                 }
186             } else {
187                 // Use the existing selector if this worker has been started.
188                 selector = this.selector;
189             }
190             assert selector != null && selector.isOpen();
191 
192             started = true;
193 
194             // "Add" the registration task to the register task queue.
195             boolean offered = registerTaskQueue.offer(channelRegTask);
196             assert offered;
197         }
198 
199         if (wakenUp.compareAndSet(false, true)) {
200             selector.wakeup();
201         }
202     }
203 
204     /**
205      * Selector loop.
206      */
207     public void run() {
208         // Store a ref to the current thread.
209         thread = Thread.currentThread();
210 
211         final Selector selector = this.selector;
212         boolean shutdown = false;
213 
214         for (;;) {
215             wakenUp.set(false);
216 
217             if (NioProviderMetadata.CONSTRAINT_LEVEL != 0) {
218                 selectorGuard.writeLock().lock();
219                 // This empty synchronization block prevents the selector from acquiring its lock.
220                 selectorGuard.writeLock().unlock();
221             }
222 
223             try {
224                 SelectorUtil.select(selector);
225 
226                 // 'wakenUp.compareAndSet(false, true)' is always evaluated
227                 // before calling 'selector.wakeup()' to reduce the wake-up
228                 // overhead. (Selector.wakeup() is an expensive operation.)
229                 //
230                 // However, there is a race condition in this approach.
231                 // The race condition is triggered when 'wakenUp' is set to
232                 // true too early.
233                 //
234                 // 'wakenUp' is set to true too early if:
235                 // 1) Selector is waken up between 'wakenUp.set(false)' and
236                 //    'selector.select(...)'. (BAD)
237                 // 2) Selector is waken up between 'selector.select(...)' and
238                 //    'if (wakenUp.get()) { ... }'. (OK)
239                 //
240                 // In the first case, 'wakenUp' is set to true and the
241                 // following 'selector.select(...)' will wake up immediately.
242                 // Until 'wakenUp' is set to false again in the next round,
243                 // 'wakenUp.compareAndSet(false, true)' will fail, and therefore
244                 // any attempt to wake up the Selector will fail, too, causing
245                 // the following 'selector.select(...)' call to block
246                 // unnecessarily.
247                 //
248                 // To fix this problem, we wake up the selector again if wakenUp
249                 // is true immediately after selector.select(...).
250                 // It is inefficient in that it wakes up the selector for both
251                 // the first case (BAD - wake-up required) and the second case
252                 // (OK - no wake-up required).
253 
254                 if (wakenUp.get()) {
255                     selector.wakeup();
256                 }
257 
258                 cancelledKeys = 0;
259                 processRegisterTaskQueue();
260                 processWriteTaskQueue();
261                 processSelectedKeys(selector.selectedKeys());
262 
263                 // Exit the loop when there's nothing to handle (the registered
264                 // key set is empty.
265                 // The shutdown flag is used to delay the shutdown of this
266                 // loop to avoid excessive Selector creation when
267                 // connections are registered in a one-by-one manner instead of
268                 // concurrent manner.
269                 if (selector.keys().isEmpty()) {
270                     if (shutdown || executor instanceof ExecutorService &&
271                             ((ExecutorService) executor).isShutdown()) {
272                         synchronized (startStopLock) {
273                             if (registerTaskQueue.isEmpty() &&
274                                     selector.keys().isEmpty()) {
275                                 started = false;
276                                 try {
277                                     selector.close();
278                                 } catch (IOException e) {
279                                     logger.warn("Failed to close a selector.",
280                                             e);
281                                 } finally {
282                                     this.selector = null;
283                                 }
284                                 break;
285                             } else {
286                                 shutdown = false;
287                             }
288                         }
289                     } else {
290                         // Give one more second.
291                         shutdown = true;
292                     }
293                 } else {
294                     shutdown = false;
295                 }
296             } catch (Throwable t) {
297                 logger.warn("Unexpected exception in the selector loop.", t);
298 
299                 // Prevent possible consecutive immediate failures that lead to
300                 // excessive CPU consumption.
301                 try {
302                     Thread.sleep(1000);
303                 } catch (InterruptedException e) {
304                     // Ignore.
305                 }
306             }
307         }
308     }
309 
310     /**
311      * Will go through all the {@link ChannelRegistionTask}s in the
312      * task queue and run them (registering them).
313      */
314     private void processRegisterTaskQueue() throws IOException {
315         for (;;) {
316             final Runnable task = registerTaskQueue.poll();
317             if (task == null) {
318                 break;
319             }
320 
321             task.run();
322             cleanUpCancelledKeys();
323         }
324     }
325 
326     /**
327      * Will go through all the WriteTasks and run them.
328      */
329     private void processWriteTaskQueue() throws IOException {
330         for (;;) {
331             final Runnable task = writeTaskQueue.poll();
332             if (task == null) {
333                 break;
334             }
335 
336             task.run();
337             cleanUpCancelledKeys();
338         }
339     }
340 
341     private void processSelectedKeys(final Set<SelectionKey> selectedKeys) throws IOException {
342         for (Iterator<SelectionKey> i = selectedKeys.iterator(); i.hasNext();) {
343             SelectionKey k = i.next();
344             i.remove();
345             try {
346                 int readyOps = k.readyOps();
347                 if ((readyOps & SelectionKey.OP_READ) != 0 || readyOps == 0) {
348                     if (!read(k)) {
349                         // Connection already closed - no need to handle write.
350                         continue;
351                     }
352                 }
353                 if ((readyOps & SelectionKey.OP_WRITE) != 0) {
354                     writeFromSelectorLoop(k);
355                 }
356             } catch (CancelledKeyException e) {
357                 close(k);
358             }
359 
360             if (cleanUpCancelledKeys()) {
361                 break; // Break the loop to avoid ConcurrentModificationException
362             }
363         }
364     }
365 
366     private boolean cleanUpCancelledKeys() throws IOException {
367         if (cancelledKeys >= NioWorker.CLEANUP_INTERVAL) {
368             cancelledKeys = 0;
369             selector.selectNow();
370             return true;
371         }
372         return false;
373     }
374 
375     /**
376      * Read is called when a Selector has been notified that the underlying channel
377      * was something to be read. The channel would previously have registered its interest
378      * in read operations.
379      *
380      * @param key The selection key which contains the Selector registration information.
381      */
382     private boolean read(final SelectionKey key) {
383         final NioDatagramChannel channel = (NioDatagramChannel) key.attachment();
384         ReceiveBufferSizePredictor predictor =
385             channel.getConfig().getReceiveBufferSizePredictor();
386         final ChannelBufferFactory bufferFactory = channel.getConfig().getBufferFactory();
387         final DatagramChannel nioChannel = (DatagramChannel) key.channel();
388 
389         // Allocating a non-direct buffer with a max udp packge size.
390         // Would using a direct buffer be more efficient or would this negatively
391         // effect performance, as direct buffer allocation has a higher upfront cost
392         // where as a ByteBuffer is heap allocated.
393         final ByteBuffer byteBuffer = ByteBuffer.allocate(
394                 predictor.nextReceiveBufferSize()).order(bufferFactory.getDefaultOrder());
395 
396         boolean failure = true;
397         SocketAddress remoteAddress = null;
398         try {
399             // Receive from the channel in a non blocking mode. We have already been notified that
400             // the channel is ready to receive.
401             remoteAddress = nioChannel.receive(byteBuffer);
402             failure = false;
403         } catch (ClosedChannelException e) {
404             // Can happen, and does not need a user attention.
405         } catch (Throwable t) {
406             fireExceptionCaught(channel, t);
407         }
408 
409         if (remoteAddress != null) {
410             // Flip the buffer so that we can wrap it.
411             byteBuffer.flip();
412 
413             int readBytes = byteBuffer.remaining();
414             if (readBytes > 0) {
415                 // Update the predictor.
416                 predictor.previousReceiveBufferSize(readBytes);
417 
418                 // Notify the interested parties about the newly arrived message.
419                 fireMessageReceived(
420                         channel, bufferFactory.getBuffer(byteBuffer), remoteAddress);
421             }
422         }
423 
424         if (failure) {
425             close(channel, succeededFuture(channel));
426             return false;
427         }
428 
429         return true;
430     }
431 
432     private void close(SelectionKey k) {
433         final NioDatagramChannel ch = (NioDatagramChannel) k.attachment();
434         close(ch, succeededFuture(ch));
435     }
436 
437     void writeFromUserCode(final NioDatagramChannel channel) {
438         /*
439          * Note that we are not checking if the channel is connected. Connected
440          * has a different meaning in UDP and means that the channels socket is
441          * configured to only send and receive from a given remote peer.
442          */
443         if (!channel.isOpen()) {
444             cleanUpWriteBuffer(channel);
445             return;
446         }
447 
448         if (scheduleWriteIfNecessary(channel)) {
449             return;
450         }
451 
452         // From here, we are sure Thread.currentThread() == workerThread.
453 
454         if (channel.writeSuspended) {
455             return;
456         }
457 
458         if (channel.inWriteNowLoop) {
459             return;
460         }
461 
462         write0(channel);
463     }
464 
465     void writeFromTaskLoop(final NioDatagramChannel ch) {
466         if (!ch.writeSuspended) {
467             write0(ch);
468         }
469     }
470 
471     void writeFromSelectorLoop(final SelectionKey k) {
472         NioDatagramChannel ch = (NioDatagramChannel) k.attachment();
473         ch.writeSuspended = false;
474         write0(ch);
475     }
476 
477     private boolean scheduleWriteIfNecessary(final NioDatagramChannel channel) {
478         final Thread workerThread = thread;
479         if (workerThread == null || Thread.currentThread() != workerThread) {
480             if (channel.writeTaskInTaskQueue.compareAndSet(false, true)) {
481                 // "add" the channels writeTask to the writeTaskQueue.
482                 boolean offered = writeTaskQueue.offer(channel.writeTask);
483                 assert offered;
484             }
485 
486             final Selector selector = this.selector;
487             if (selector != null) {
488                 if (wakenUp.compareAndSet(false, true)) {
489                     selector.wakeup();
490                 }
491             }
492             return true;
493         }
494 
495         return false;
496     }
497 
498     private void write0(final NioDatagramChannel channel) {
499 
500         boolean addOpWrite = false;
501         boolean removeOpWrite = false;
502 
503         long writtenBytes = 0;
504 
505         final SocketSendBufferPool sendBufferPool = this.sendBufferPool;
506         final DatagramChannel ch = channel.getDatagramChannel();
507         final Queue<MessageEvent> writeBuffer = channel.writeBufferQueue;
508         final int writeSpinCount = channel.getConfig().getWriteSpinCount();
509         synchronized (channel.writeLock) {
510             // inform the channel that write is in-progress
511             channel.inWriteNowLoop = true;
512 
513             // loop forever...
514             for (;;) {
515                 MessageEvent evt = channel.currentWriteEvent;
516                 SendBuffer buf;
517                 if (evt == null) {
518                     if ((channel.currentWriteEvent = evt = writeBuffer.poll()) == null) {
519                         removeOpWrite = true;
520                         channel.writeSuspended = false;
521                         break;
522                     }
523 
524                     channel.currentWriteBuffer = buf = sendBufferPool.acquire(evt.getMessage());
525                 } else {
526                     buf = channel.currentWriteBuffer;
527                 }
528 
529                 try {
530                     long localWrittenBytes = 0;
531                     SocketAddress raddr = evt.getRemoteAddress();
532                     if (raddr == null) {
533                         for (int i = writeSpinCount; i > 0; i --) {
534                             localWrittenBytes = buf.transferTo(ch);
535                             if (localWrittenBytes != 0) {
536                                 writtenBytes += localWrittenBytes;
537                                 break;
538                             }
539                             if (buf.finished()) {
540                                 break;
541                             }
542                         }
543                     } else {
544                         for (int i = writeSpinCount; i > 0; i --) {
545                             localWrittenBytes = buf.transferTo(ch, raddr);
546                             if (localWrittenBytes != 0) {
547                                 writtenBytes += localWrittenBytes;
548                                 break;
549                             }
550                             if (buf.finished()) {
551                                 break;
552                             }
553                         }
554                     }
555 
556                     if (localWrittenBytes > 0 || buf.finished()) {
557                         // Successful write - proceed to the next message.
558                         buf.release();
559                         ChannelFuture future = evt.getFuture();
560                         channel.currentWriteEvent = null;
561                         channel.currentWriteBuffer = null;
562                         evt = null;
563                         buf = null;
564                         future.setSuccess();
565                     } else {
566                         // Not written at all - perhaps the kernel buffer is full.
567                         addOpWrite = true;
568                         channel.writeSuspended = true;
569                         break;
570                     }
571                 } catch (final AsynchronousCloseException e) {
572                     // Doesn't need a user attention - ignore.
573                 } catch (final Throwable t) {
574                     buf.release();
575                     ChannelFuture future = evt.getFuture();
576                     channel.currentWriteEvent = null;
577                     channel.currentWriteBuffer = null;
578                     buf = null;
579                     evt = null;
580                     future.setFailure(t);
581                     fireExceptionCaught(channel, t);
582                 }
583             }
584             channel.inWriteNowLoop = false;
585         }
586 
587         fireWriteComplete(channel, writtenBytes);
588 
589         if (addOpWrite) {
590             setOpWrite(channel);
591         } else if (removeOpWrite) {
592             clearOpWrite(channel);
593         }
594     }
595 
596     private void setOpWrite(final NioDatagramChannel channel) {
597         Selector selector = this.selector;
598         SelectionKey key = channel.getDatagramChannel().keyFor(selector);
599         if (key == null) {
600             return;
601         }
602         if (!key.isValid()) {
603             close(key);
604             return;
605         }
606 
607         // interestOps can change at any time and at any thread.
608         // Acquire a lock to avoid possible race condition.
609         synchronized (channel.interestOpsLock) {
610             int interestOps = channel.getRawInterestOps();
611             if ((interestOps & SelectionKey.OP_WRITE) == 0) {
612                 interestOps |= SelectionKey.OP_WRITE;
613                 key.interestOps(interestOps);
614                 channel.setRawInterestOpsNow(interestOps);
615             }
616         }
617     }
618 
619     private void clearOpWrite(NioDatagramChannel channel) {
620         Selector selector = this.selector;
621         SelectionKey key = channel.getDatagramChannel().keyFor(selector);
622         if (key == null) {
623             return;
624         }
625         if (!key.isValid()) {
626             close(key);
627             return;
628         }
629 
630         // interestOps can change at any time and at any thread.
631         // Acquire a lock to avoid possible race condition.
632         synchronized (channel.interestOpsLock) {
633             int interestOps = channel.getRawInterestOps();
634             if ((interestOps & SelectionKey.OP_WRITE) != 0) {
635                 interestOps &= ~SelectionKey.OP_WRITE;
636                 key.interestOps(interestOps);
637                 channel.setRawInterestOpsNow(interestOps);
638             }
639         }
640     }
641 
642     static void disconnect(NioDatagramChannel channel, ChannelFuture future) {
643         boolean connected = channel.isConnected();
644         try {
645             channel.getDatagramChannel().disconnect();
646             future.setSuccess();
647             if (connected) {
648                 fireChannelDisconnected(channel);
649             }
650         } catch (Throwable t) {
651             future.setFailure(t);
652             fireExceptionCaught(channel, t);
653         }
654     }
655 
656     void close(final NioDatagramChannel channel,
657             final ChannelFuture future) {
658         boolean connected = channel.isConnected();
659         boolean bound = channel.isBound();
660         try {
661             channel.getDatagramChannel().close();
662             cancelledKeys ++;
663 
664             if (channel.setClosed()) {
665                 future.setSuccess();
666                 if (connected) {
667                     fireChannelDisconnected(channel);
668                 }
669                 if (bound) {
670                     fireChannelUnbound(channel);
671                 }
672 
673                 cleanUpWriteBuffer(channel);
674                 fireChannelClosed(channel);
675             } else {
676                 future.setSuccess();
677             }
678         } catch (Throwable t) {
679             future.setFailure(t);
680             fireExceptionCaught(channel, t);
681         }
682     }
683 
684     private void cleanUpWriteBuffer(final NioDatagramChannel channel) {
685         Exception cause = null;
686         boolean fireExceptionCaught = false;
687 
688         // Clean up the stale messages in the write buffer.
689         synchronized (channel.writeLock) {
690             MessageEvent evt = channel.currentWriteEvent;
691             if (evt != null) {
692                 // Create the exception only once to avoid the excessive overhead
693                 // caused by fillStackTrace.
694                 if (channel.isOpen()) {
695                     cause = new NotYetConnectedException();
696                 } else {
697                     cause = new ClosedChannelException();
698                 }
699 
700                 ChannelFuture future = evt.getFuture();
701                 channel.currentWriteBuffer.release();
702                 channel.currentWriteBuffer = null;
703                 channel.currentWriteEvent = null;
704                 evt = null;
705                 future.setFailure(cause);
706                 fireExceptionCaught = true;
707             }
708 
709             Queue<MessageEvent> writeBuffer = channel.writeBufferQueue;
710             if (!writeBuffer.isEmpty()) {
711                 // Create the exception only once to avoid the excessive overhead
712                 // caused by fillStackTrace.
713                 if (cause == null) {
714                     if (channel.isOpen()) {
715                         cause = new NotYetConnectedException();
716                     } else {
717                         cause = new ClosedChannelException();
718                     }
719                 }
720 
721                 for (;;) {
722                     evt = writeBuffer.poll();
723                     if (evt == null) {
724                         break;
725                     }
726                     evt.getFuture().setFailure(cause);
727                     fireExceptionCaught = true;
728                 }
729             }
730         }
731 
732         if (fireExceptionCaught) {
733             fireExceptionCaught(channel, cause);
734         }
735     }
736 
737     void setInterestOps(final NioDatagramChannel channel,
738             ChannelFuture future, int interestOps) {
739 
740         boolean changed = false;
741         try {
742             // interestOps can change at any time and by any thread.
743             // Acquire a lock to avoid possible race condition.
744             synchronized (channel.interestOpsLock) {
745                 final Selector selector = this.selector;
746                 final SelectionKey key = channel.getDatagramChannel().keyFor(selector);
747 
748                 if (key == null || selector == null) {
749                     // Not registered to the worker yet.
750                     // Set the rawInterestOps immediately; RegisterTask will pick it up.
751                     channel.setRawInterestOpsNow(interestOps);
752                     return;
753                 }
754 
755                 // Override OP_WRITE flag - a user cannot change this flag.
756                 interestOps &= ~Channel.OP_WRITE;
757                 interestOps |= channel.getRawInterestOps() & Channel.OP_WRITE;
758 
759                 switch (NioProviderMetadata.CONSTRAINT_LEVEL) {
760                 case 0:
761                     if (channel.getRawInterestOps() != interestOps) {
762                         // Set the interesteOps on the SelectionKey
763                         key.interestOps(interestOps);
764                         // If the worker thread (the one that that might possibly be blocked
765                         // in a select() call) is not the thread executing this method wakeup
766                         // the select() operation.
767                         if (Thread.currentThread() != thread &&
768                                 wakenUp.compareAndSet(false, true)) {
769                             selector.wakeup();
770                         }
771                         changed = true;
772                     }
773                     break;
774                 case 1:
775                 case 2:
776                     if (channel.getRawInterestOps() != interestOps) {
777                         if (Thread.currentThread() == thread) {
778                             // Going to set the interestOps from the same thread.
779                             // Set the interesteOps on the SelectionKey
780                             key.interestOps(interestOps);
781                             changed = true;
782                         } else {
783                             // Going to set the interestOps from a different thread
784                             // and some old provides will need synchronization.
785                             selectorGuard.readLock().lock();
786                             try {
787                                 if (wakenUp.compareAndSet(false, true)) {
788                                     selector.wakeup();
789                                 }
790                                 key.interestOps(interestOps);
791                                 changed = true;
792                             } finally {
793                                 selectorGuard.readLock().unlock();
794                             }
795                         }
796                     }
797                     break;
798                 default:
799                     throw new Error();
800                 }
801                 if (changed) {
802                     channel.setRawInterestOpsNow(interestOps);
803                 }
804             }
805 
806             future.setSuccess();
807             if (changed) {
808                 fireChannelInterestChanged(channel);
809             }
810         } catch (final CancelledKeyException e) {
811             // setInterestOps() was called on a closed channel.
812             ClosedChannelException cce = new ClosedChannelException();
813             future.setFailure(cce);
814             fireExceptionCaught(channel, cce);
815         } catch (final Throwable t) {
816             future.setFailure(t);
817             fireExceptionCaught(channel, t);
818         }
819     }
820 
821     /**
822      * RegisterTask is a task responsible for registering a channel with a
823      * selector.
824      */
825     private final class ChannelRegistionTask implements Runnable {
826         private final NioDatagramChannel channel;
827 
828         private final ChannelFuture future;
829 
830         ChannelRegistionTask(final NioDatagramChannel channel,
831                 final ChannelFuture future) {
832             this.channel = channel;
833             this.future = future;
834         }
835 
836         /**
837          * This runnable's task. Does the actual registering by calling the
838          * underlying DatagramChannels peer DatagramSocket register method.
839          *
840          */
841         public void run() {
842             final SocketAddress localAddress = channel.getLocalAddress();
843             if (localAddress == null) {
844                 if (future != null) {
845                     future.setFailure(new ClosedChannelException());
846                 }
847                 close(channel, succeededFuture(channel));
848                 return;
849             }
850 
851             try {
852                 synchronized (channel.interestOpsLock) {
853                     channel.getDatagramChannel().register(
854                             selector, channel.getRawInterestOps(), channel);
855                 }
856                 if (future != null) {
857                     future.setSuccess();
858                 }
859             } catch (final ClosedChannelException e) {
860                 if (future != null) {
861                     future.setFailure(e);
862                 }
863                 close(channel, succeededFuture(channel));
864                 throw new ChannelException(
865                         "Failed to register a socket to the selector.", e);
866             }
867         }
868     }
869 }