Do not close ServerChannel on IOException while accepting an incoming…

… connection

.. so that we can recover from 'too many open files'

- Fixes netty#1578

transport/src/main/java/io/netty/channel/nio/AbstractNioMessageChannel.java

@@ -18,6 +18,7 @@
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelConfig;
 import io.netty.channel.ChannelPipeline;
+import io.netty.channel.ServerChannel;
 
 import java.io.IOException;
 import java.nio.channels.SelectableChannel;
@@ -91,7 +92,9 @@ public void read() {
 
             if (exception != null) {
                 if (exception instanceof IOException) {
-                    closed = true;
+                    // ServerChannel should not be closed even on IOException because it can often continue
+                    // accepting incoming connections. (e.g. too many open files)
+                    closed = !(AbstractNioMessageChannel.this instanceof ServerChannel);
                 }
 
                 pipeline.fireExceptionCaught(exception);