[python-win32] PyWin32 - PostMessage return value

[Gabriel Genellina]

At Saturday 20/1/2007 21:35, jbd wrote:

>I create a process via the CreateProcess function, and i wait using
>WaitForInputIdle to be sure that the process is in ready state, it works
>well (ie: the process is launched).

Check also whether WaitForInputIdle returns 0, and not WAIT_TIMEOUT 
(meaning that the process is not ready yet)

>I send a message via PostMessage and
>i'd like to know if the command had been correctly processed, and i don't
>know how to do it.
>
>But, although the application is in ready state, some hardware
>initialization has to be done and seems not to be accomplished when
>WaitForInputIdle returns. The message i posted using PostMessage is
>correctly processed, but nothing appends since the ressource i need were
>not yet initialized. If i introduce a time.sleep(2) between the
>WaitForInputIdle and the PostMessage function, everything is working fine.

And the sleep isn't an acceptable solution, I presume.
You can use some form of interprocess communication; coming from a 
Unix environment you may know some of them, like pipes,  queues. Or a 
synchornization mechanism like a semaphore.
But since you're already using messages, maybe the easiest way is 
making the target application broadcast a message telling "I'm ready 
now", and when the caller sees it, it knows it can post the message.
Use RegisterWindowMessage on both applications, with the same name, 
to obtain a unique message identifier.
Use HWND_BROADCAST as the first argument to PostMessage to broadcast 
it to all top level windows.

>On the msdn site, the PostMessage function returns a BOOL, but since this
>is an asynchrone function, the return value just means that the message
>has been posted without problem. Am i correct ? By the way, how do i check
>for this return value with pywin32 ? All message related function seems to
>return None.

Yes, it appears that you cannot retrieve the return value of 
PostMessage. Anyway it won't tell you much.
The caller can communicate its own window handle to the target 
application, using the wParam or lParam arguments when it sends some 
message. This way, the target application can reply to the caller 
when he has completed processing the operation (either ok or with an error).


-- 
Gabriel Genellina
Softlab SRL 


	

	
		
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