[#681] Allow a user to access the Selector of an EventLoop

- Make NioEventLoop public so that a user can downcast it
- Add NioEventLoop.register()
- Add NioTask to let user specify what to do on select()

transport/src/main/java/io/netty/channel/socket/nio/NioEventLoop.java

@@ -18,6 +18,7 @@ package io.netty.channel.socket.nio;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelException;
 import io.netty.channel.ChannelTaskScheduler;
+import io.netty.channel.EventLoopException;
 import io.netty.channel.SingleThreadEventLoop;
 import io.netty.channel.socket.nio.AbstractNioChannel.NioUnsafe;
 import io.netty.logging.InternalLogger;
@@ -25,7 +26,6 @@ import io.netty.logging.InternalLoggerFactory;
 
 import java.io.IOException;
 import java.nio.channels.CancelledKeyException;
-import java.nio.channels.ClosedChannelException;
 import java.nio.channels.SelectableChannel;
 import java.nio.channels.SelectionKey;
 import java.nio.channels.Selector;
@@ -44,7 +44,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
  * {@link Selector} and so does the multi-plexing of these in the event loop.
  *
  */
-final class NioEventLoop extends SingleThreadEventLoop {
+public final class NioEventLoop extends SingleThreadEventLoop {
 
     /**
      * Internal Netty logger.
@@ -97,39 +97,76 @@ final class NioEventLoop extends SingleThreadEventLoop {
         return new ConcurrentLinkedQueue<Runnable>();
     }
 
+    /**
+     * Registers an arbitrary {@link SelectableChannel}, not necessarily created by Netty, to the {@link Selector}
+     * of this event loop.  Once the specified {@link SelectableChannel} is registered, the specified {@code task} will
+     * be executed by this event loop when the {@link SelectableChannel} is ready.
+     */
+    public void register(final SelectableChannel ch, final int interestOps, final NioTask<?> task) {
+        if (ch == null) {
+            throw new NullPointerException("ch");
+        }
+        if (interestOps == 0) {
+            throw new IllegalArgumentException("interestOps must be non-zero.");
+        }
+        if ((interestOps & ~ch.validOps()) != 0) {
+            throw new IllegalArgumentException(
+                    "invalid interestOps: " + interestOps + "(validOps: " + ch.validOps() + ")");
+        }
+        if (task == null) {
+            throw new NullPointerException("task");
+        }
+
+        if (isShutdown()) {
+            throw new IllegalStateException("event loop shut down");
+        }
+
+        try {
+            ch.register(selector, interestOps, task);
+        } catch (Exception e) {
+            throw new EventLoopException("failed to register a channel", e);
+        }
+    }
+
     // Create a new selector and "transfer" all channels from the old
     // selector to the new one
     private Selector recreateSelector() {
-        Selector newSelector = openSelector();
+        final Selector newSelector = openSelector();
-        Selector selector = this.selector;
+        final Selector oldSelector = this.selector;
-        this.selector = newSelector;
 
-        // loop over all the keys that are registered with the old Selector
+        // Register all channels to the new Selector.
-        // and register them with the new one
+        boolean success = false;
-        for (SelectionKey key: selector.keys()) {
+        try {
-            SelectableChannel ch = key.channel();
+            for (SelectionKey key: oldSelector.keys()) {
-            int ops = key.interestOps();
+                key.channel().register(newSelector, key.interestOps(), key.attachment());
-            Object att = key.attachment();
+            }
-            // cancel the old key
+            success = true;
-            cancel(key);
+        } catch (Exception e) {
-
+            logger.warn("Failed to re-register a Channel to the new Selector.", e);
-            try {
+        } finally {
-                // register the channel with the new selector now
+            if (!success) {
-                ch.register(newSelector, ops, att);
+                try {
-            } catch (ClosedChannelException e) {
+                    newSelector.close();
-                // close channel
+                } catch (Exception e) {
-                AbstractNioChannel channel = (AbstractNioChannel) att;
+                    logger.warn("Failed to close the new Selector.", e);
-                channel.unsafe().close(channel.unsafe().voidFuture());
+                }
             }
         }
-        try {
+
-            // time to close the old selector as everything else is registered to the new one
+        if (!success) {
-            selector.close();
+            // Keep using the old Selector on failure.
-        } catch (Throwable t) {
+            return oldSelector;
-            logger.warn("Failed to close a selector.", t);
         }
-        logger.warn("Recreated Selector because of possible jdk epoll(..) bug");
+
-        return newSelector;
+        // Registration to the new Selector is done. Close the old Selector to cancel all old keys.
+        try {
+            selector.close();
+        } catch (Exception e) {
+            logger.warn("Failed to close the old selector.", e);
+        }
+
+        logger.info("Selector migration complete.");
+        return this.selector = newSelector;
     }
 
     @Override
@@ -266,25 +303,11 @@ final class NioEventLoop extends SingleThreadEventLoop {
         try {
             for (i = selectedKeys.iterator(); i.hasNext();) {
                 final SelectionKey k = i.next();
-                final AbstractNioChannel ch = (AbstractNioChannel) k.attachment();
+                final Object a = k.attachment();
-                final NioUnsafe unsafe = ch.unsafe();
+                if (a instanceof AbstractNioChannel) {
-                try {
+                    processSelectedKey(k, (AbstractNioChannel) a);
-                    int readyOps = k.readyOps();
+                } else {
-                    if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
+                    processSelectedKey(k, (NioTask<SelectableChannel>) a);
-                        unsafe.read();
-                        if (!ch.isOpen()) {
-                            // Connection already closed - no need to handle write.
-                            continue;
-                        }
-                    }
-                    if ((readyOps & SelectionKey.OP_WRITE) != 0) {
-                        unsafe.flushNow();
-                    }
-                    if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
-                        unsafe.finishConnect();
-                    }
-                } catch (CancelledKeyException ignored) {
-                    unsafe.close(unsafe.voidFuture());
                 }
 
                 if (cleanedCancelledKeys) {
@@ -304,12 +327,58 @@ final class NioEventLoop extends SingleThreadEventLoop {
         }
     }
 
+    private static void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
+        final NioUnsafe unsafe = ch.unsafe();
+        try {
+            int readyOps = k.readyOps();
+            if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
+                unsafe.read();
+                if (!ch.isOpen()) {
+                    // Connection already closed - no need to handle write.
+                    return;
+                }
+            }
+            if ((readyOps & SelectionKey.OP_WRITE) != 0) {
+                unsafe.flushNow();
+            }
+            if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
+                unsafe.finishConnect();
+            }
+        } catch (CancelledKeyException ignored) {
+            unsafe.close(unsafe.voidFuture());
+        }
+    }
+
+    private static void processSelectedKey(SelectionKey k, NioTask<SelectableChannel> task) {
+        boolean success = false;
+        try {
+            task.channelReady(k.channel(), k);
+            success = true;
+        } catch (Exception e) {
+            logger.warn("Unexpected exception while running NioTask.channelReady() - cancelling the key", e);
+        } finally {
+            if (!success) {
+                k.cancel();
+            }
+
+            if (!k.isValid()) { // Either cancelled by channelReady() or by this method.
+                invokeChannelUnregistered(task, k);
+            }
+        }
+    }
+
     private void closeAll() {
         SelectorUtil.cleanupKeys(selector);
         Set<SelectionKey> keys = selector.keys();
         Collection<Channel> channels = new ArrayList<Channel>(keys.size());
         for (SelectionKey k: keys) {
-            channels.add((Channel) k.attachment());
+            Object a = k.attachment();
+            if (a instanceof Channel) {
+                channels.add((Channel) a);
+            } else {
+                k.cancel();
+                invokeChannelUnregistered((NioTask<SelectableChannel>) a, k);
+            }
         }
 
         for (Channel ch: channels) {
@@ -317,6 +386,14 @@ final class NioEventLoop extends SingleThreadEventLoop {
         }
     }
 
+    private static void invokeChannelUnregistered(NioTask<SelectableChannel> task, SelectionKey k) {
+        try {
+            task.channelUnregistered(k.channel());
+        } catch (Exception e) {
+            logger.warn("Unexpected exception while running NioTask.channelUnregistered()", e);
+        }
+    }
+
     @Override
     protected void wakeup(boolean inEventLoop) {
         if (wakenUp.compareAndSet(false, true)) {

transport/src/main/java/io/netty/channel/socket/nio/NioTask.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2012 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.channel.socket.nio;
+
+import java.nio.channels.SelectableChannel;
+import java.nio.channels.SelectionKey;
+
+/**
+ * An arbitrary task that can be executed by {@link NioEventLoop} when a {@link SelectableChannel} becomes ready.
+ *
+ * @see NioEventLoop#register(SelectableChannel, int, NioTask)
+ */
+public interface NioTask<C extends SelectableChannel> {
+    /**
+     * Invoked when the {@link SelectableChannel} has been selected by the {@link java.nio.channels.Selector}.
+     */
+    void channelReady(C ch, SelectionKey key) throws Exception;
+
+    /**
+     * Invoked when the {@link SelectionKey} of the specified {@link SelectableChannel} has been cancelled and thus
+     * this {@link NioTask} will not be notified anymore.
+     */
+    void channelUnregistered(C ch) throws Exception;
+}