question about synchronous message passing

QNX DEVELOPERS General Programming
1

Hi,

I want to implement synchronous communication between two computers(A, B) with the Qnet and gns. My problem is sometimes I need A to be server, and sometimes the B to be server. Could this situation be done? Any suggestions?

Thanks in advance!

Juvin

2

There are a few different approaches. The symmetric solution would be to have a server and client on each side. If the server and client needs to be in the same process, you could use threads.

Another approach is to realize that a message passing server can look like a client. A visual might help:

Normal Mode

Client --------------------- sends message -------> Server
server does something
Client <-------------------- reply message ------- Server
Repeat

Reverse Mode

Client Checks in ------------- send message -------> Server receives but does not reply
Server wants to act like a client now
Client <---------------------- reply message -------- Server replies with message
Client does something
Client responds --------------send message --------> Server receives but does not reply
Repeat

3

Thanks for you reply!

I noticed that always client sends message first and server reply message. Could this be reversed?
Such as server name_attach some global name, send messages then client name_open that global name and receive message, can this situation be done?

Thanks again!

4

You can build something with QNX message passing that works this way, but the answer to your question is no, there is no way to send a message before a process has set up a channel to receive the message.

5

Thanks a lot.
Could you give me a hint to do QNX message passing in a distributed way execept tcp/udp?

6

If you mean that you want to broadcast, there is no way that will have the efficiency of udp. You would have to have multiple messages sent and/or received.

7

Thanks for your help, I think UDP maybe a good choice.