Re: [Tnfox-discussion] IPC message sending problems

[Niall D. <s_s...@ne...>]

On 6 Oct 2008 at 17:37, Ck wrote:

My apologies for the very late reply - my entire email processing 
system died for most of last week and it took the past weekend to 
extract my email.

> One more question.
> 
> Can't understand how to get ask from thread via IPC..
> 
> For example:
> thread_1 requests from thread_2 some actions and wants to get the
> result of this actions.
> 
> void thread_1::req()
> {
>   Msg msg(bla-bla);
>   sendMsg(msg);
> 
>   // here i want to use result from thread_2.
> }
> 
> ..
> thread_2::msgReceived(FXIPCMsg *rawmsg)
> {
>   Msg *i = (Msg*)rawmsg;
> 
>   FXString result = someAction(i->data);
> }
> 
> How to return result to thread_1?

You need to define an Ack message for the message which will 
transport your result back to the sender. Your sender can either wait 
for the reply or move on with other processing, polling for the reply 
or indeed having a separate handler for the reply whenever it 
arrives.

If you have an Ack message defined, TnFOX will automatically collect 
any C++ exceptions thrown by the remote side and return them to the 
message sender. I vaguely remember a system in place for timeouts as 
well, so if a message does not return in time you get notified and 
the operation is cancelled.

If you check the TestIPC program for the "file access over IPC" 
mechanism then this gives a good demonstration of how to efficiently 
use Ack messages to maximise throughput and deal correctly with error 
situations.

HTH,
Niall