blocking when sending lots of data

["이희승 (Trustin Lee)"]

On 07/07/2009 03:05 AM, mra wrote:
> thanks trustin.
> 
> i see that you use java.util.Queue.offer() in ChunkedWriteHandler to
> account for the downstream message, which doesn't block if queue's
> capacity is full. so it seems as though excess netty messages are
> simply dropped (line 98 in 3.1.0.CR1).

Yes, nothing blocks there.  It's not dropped actually, but just queue
for later write.

> so could you suggest an implementation that would actually block the
> writer, if more data is being generated via netty than can be handled
> by the underlying o/s's tcp/ip implementation?

You could use a lock to implement blocking operation.  For example:

// Blocking write
synchronized (lock) {
  while (!ch.isWritable()) {
    lock.wait();
  }
  ch.write(something);
}

// Unblock the wait() call in channelInterestChanged()
synchronized (lock) {
  if (evt.getChannel().isWritable()) {
    lock.notify();
  }
}

I would still recommend you to try event-driven approach I demonstrated
in ChunkedWriteHandler if possible.

HTH,
Trustin