[#1310] Fix deadlock which can happen if limit of MemoryAwareThreadPoolExecutor was exceed and an exceptionCaught(..) is triggered by a write

src/main/java/org/jboss/netty/channel/socket/nio/AbstractNioWorker.java

@@ -31,7 +31,9 @@ import java.nio.channels.NotYetConnectedException;
 import java.nio.channels.SelectionKey;
 import java.nio.channels.Selector;
 import java.nio.channels.WritableByteChannel;
+import java.util.ArrayList;
 import java.util.Iterator;
+import java.util.List;
 import java.util.Queue;
 import java.util.Set;
 import java.util.concurrent.Executor;
@@ -171,6 +173,8 @@ abstract class AbstractNioWorker extends AbstractNioSelector implements Worker {
         final WritableByteChannel ch = channel.channel;
         final Queue<MessageEvent> writeBuffer = channel.writeBufferQueue;
         final int writeSpinCount = channel.getConfig().getWriteSpinCount();
+        List<Throwable> causes = null;
+
         synchronized (channel.writeLock) {
             channel.inWriteNowLoop = true;
             for (;;) {
@@ -245,7 +249,14 @@ abstract class AbstractNioWorker extends AbstractNioSelector implements Worker {
                         future.setFailure(t);
                     }
                     if (iothread) {
-                        fireExceptionCaught(channel, t);
+                        // An exception was thrown from within a write in the iothread. We store a reference to it
+                        // in a list for now and notify the handlers in the chain after the writeLock was released
+                        // to prevent possible deadlock.
+                        // See #1310
+                        if (causes == null) {
+                            causes = new ArrayList<Throwable>(1);
+                        }
+                        causes.add(t);
                     } else {
                         fireExceptionCaughtLater(channel, t);
                     }
@@ -273,11 +284,18 @@ abstract class AbstractNioWorker extends AbstractNioSelector implements Worker {
                 } else if (removeOpWrite) {
                     clearOpWrite(channel);
                 }
-            } else {
-                // close the channel now
-                close(channel, succeededFuture(channel));
             }
         }
+        if (causes != null) {
+            for (Throwable cause: causes) {
+                // notify about cause now as it was triggered in the write loop
+                fireExceptionCaught(channel, cause);
+            }
+        }
+        if (!open) {
+            // close the channel now
+            close(channel, succeededFuture(channel));
+        }
         if (iothread) {
             fireWriteComplete(channel, writtenBytes);
         } else {