Trustin Lee <[EMAIL PROTECTED]> writes: > But you can check the number of buffered messages by calling > IoSession.getScheduledWrites() or the number of buffered bytes by > calling IoSession.getScheduledWriteBytes(), so you can stop writing > additional messages by checking the value whenever you write a > message. once a message is flushed out, messageWritten() event is > invoked, so you can get notified, too.
I see. That's not quite the same thing that ACE (and java.nio.channels.spi.AbstractSelector) provides. > It would be best if there's an automated way to control the flow, > but didn't find what the best way is yet. You could give us an > idea. Well, I do see the java.nio.SelectionKey.OP_WRITE interest operation.¹ That sounds like it's there to detect precisely the same events that ACE_Event_Handle::handle_output() advises. I wouldn't expect this OP_WRITE notification to necessarily be visible at the MINA user level, as MINA is already handling outbound message queuing and hence insulating the user from the actual pushing of buffers into the socket. Take a look at Section 5.5 (pages 16 and 17) of /The Design and Use of the ACE Reactor/.² There, the authors show how to request OP_WRITE wakeup/notification if the outbound message queue is not empty, and how to cancel such notification when the queue is drained. It's possible that the message queue has messages in it, but the socket's buffer is sufficiently congested that no more data can be pushed in. Registering for OP_WRITE notification allows the queue worker to wait until the socket is ready to accept more data. I've just started poking through MINA's socket output code. It looks like some points where OP_WRITE registration/notification could be relevant are in org.apache.mina.transport.socket.nio.SocketFilterChain.doWrite() and org.apache.mina.transport.socket.nio.SocketIoProcessor.process() But I kept looking and just found SocketIoProcessor.doFlush(), which registers for the OP_WRITE interest when its attempt to write an entire buffer falls short. Similar behavior is in SocketIoProcessor.doUpdateTrafficMask(). Well, I'll stop there. It looks like a lot of what I'm describing is already built into MINA. It's just hidden nicely from the user, perhaps as it should be. Footnotes: ¹ http://java.sun.com/javase/6/docs/api/java/nio/channels/SelectionKey.html#OP_WRITE ² http://www.cse.wustl.edu/~doc/pspdfs/reactor-rules.pdf -- Steven E. Harris
