CODEWITHSUNDEEP
javanettynio
Mavo
Mavo

Reputation: 625

Netty client uses only one thread

I'm implementing a binary protocol above TCP/IP and using Netty to achieve this. My problem is that the performance is rather poor (600 msg/s). I'm connecting as a client to a server with one connection only. When I investigated running instance with JTop I saw that Netty was using 1 worker thread very heavily and the other 5 worker threads are doing nothing (0% ussage). I was digging on the web and all I found is mention of ExecutionHandler. But why should I use this if those 6 worker threads should be enough. Or am I misunderstanding how Netty uses these threads?

My Netty init code:

this.channelFactory = new NioClientSocketChannelFactory(this.executors, DaemonExecutors.newCachedDaemonThreadPool(), 1, 6);
this.clientBootstrap = new ClientBootstrap(channelFactory);
this.channelGroupHandler = new ClientChannelGroupHandler(this.channels);
this.clientBootstrap.getPipeline().addLast("ChannelGroupHandler", this.channelGroupHandler);

Thanks for any hints Matous

Upvotes: 0

Views: 5951

Answers (2)

Enno Shioji
Enno Shioji

Reputation: 26882

The reason you only see one worker thread being used is because you are making only a single connection to the server. Had you made multiple connections, more worker threads would have been used.

If each connection's work is suited for parallelization, then you can implement a handler that uses threads internally, but Netty won't to do that for you.

As for the NIO/OIO distinction, it's true that the idea of NIO is to have one thread handling the events for multiple connections. However, this doesn't mean one thread will handle the all the work. The "single thread" only dispatches work to other (i.e. worker) threads.

Here is an excerpt from the Netty doc:

How threads work There are two types of threads in a NioServerSocketChannelFactory; one is boss thread and the other is worker thread.

Boss threads Each bound ServerSocketChannel has its own boss thread. For example, if you opened two server ports such as 80 and 443, you will have two boss threads. A boss thread accepts incoming connections until the port is unbound. Once a connection is accepted successfully, the boss thread passes the accepted Channel to one of the worker threads that the NioServerSocketChannelFactory manages.

Worker threads One NioServerSocketChannelFactory can have one or more worker threads. A worker thread performs non-blocking read and write for one or more Channels in a non-blocking mode.

Upvotes: 0

Kayaman
Kayaman

Reputation: 73578

NIO, or rather the non-blocking version of NIO ("New" I/O) allows you to use a single thread for multiple connections, since the thread doesn't block (hence the name) on the read/write operations. Blocking I/O requires a thread for each connection, as the blocking would prevent you from handling traffic between different connections.

This allows you to perform more efficient communication, since you no longer have thread overhead for one.

A decent tutorial is available here (the original Oracle tutorial seems to have vanished from the face of the Google).

Upvotes: 2

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