Reading/ Writing Socket in order

Question

Hi, I have a client / sever model which I'm finding very hard to implement, it is this way:
I've got a server which clients connect to, every client can fire events in other clients, example: a client sends a file to be re-sent to other clients, other events can be: to create/delete/modify a new user, a new group, and so on.
I need all the traffic to pass through the server in order to raise other clients, there can't be direct conexions between clients. I create 2 threads on the client side (1 for reading n 1 for writing from/to the server).
On the server side I've got a thread to listen to conexions, and 1 thread to read/write from/to every client. I also keep a list with references to every thread, that's the way I use to notify other threads that an event has happened.
That model genarates a lot of problems since there's just one socket per client, problems are like this: supposing the case the server needs to send a file (which is divided in packets) to client A, so the thread that keeps the conexion (thread A) with client A, first send a notification so the client (who gets ready to receive the file) and then starts to send the file, but it cant finish 'cause its processor time ends.
In that moment (while the client it's still waiting for the last packets of the file), another thread (thread B) starts, it needs to send info of another event (a new client created for example) to a bunch of clients, including client A who is still waiting for packets of the file, when client A receive the info of the other event, it can't know the difference so save that info as a part of the file, creating a corrupted file.
Try to synchronize that, it's difficult, cause bloking all the threads 'till 1 finish to sent, affect a lot the efficience of the system
I do appreciate any kind of help or idea

Answer 1

there are plenty of alternatives, but one very simple is to not allow other threads send data through a socket, but instead put what you want to send on a queue (you can use Vector for simplicity or the new Queue implementations)... the actual transfering happens on the thread that "owns" a socket.... this thread checks for objects in that queue, removing from that and sending as needed...
having another queue for incoming data (before processing) is a good idea too (i think)...
if its for learning pourposes, it will work fine... if you want a large scale system, try learning JAVA NIO packages that needs lesser threads...