suggestion on a complicated inter-process communication

[norseman]

Way wrote:
> Hello friends,
> 
> I have a little messy situation on IPC. Please if you can, give me
> some suggestion on how to implement. Thanks a lot!
> 
> -> denotes create
> 
> 
> MainProcess -> Process1 -> Process3 (from os.system)
>                    |
>                     -> Process2 (from os.system) -> Process4 (from
> os.system) ->Process5
> 
> I would like to make the communication between Process1 and Process5.
> Process1 needs Process5's output to provide argument to generate
> Process3, and in turn Process5 needs to wait Process3 finished.
> 
> Thank you very much if you can give a hint.
> 
> --
> http://mail.python.org/mailman/listinfo/python-list
> 
=====================================

My first reaction is to use named pipes.

Process1 -> P2 -> P4 -> Process5 >>NamedPipe (P5 outputs to NamedPipe)
    Process1 waits for NamedPipe to be made and starts creating Process3
    When Process3 is finished it can set an OS level environmental or
      create a dummy file as a signal to Process5 to finish.
    P1 becomes orchestrator, NamedPipe is courier, file is smoke signal.

This method works when IPC is not a good choice. (Like independent child 
processes run across the net. A specific file in a specific location 
effectively creates a specific signal. Whether or not contents are used 
or even existing is programmer choice.)

Hope this helps.

Steve