[DUG] Sending notification between programs

[Dennis Chuah]

John,

Hi.  What you want to use is WinAPI: FindFirstChangeNotification, 
FindNextChangeNotification and FindCloseChangeNotification in program B. 
Essentially, A writes to a file, and renames it.  This causes the handle 
returned by FindFirstChangeNotification to be signaled.  You can test for 
this using a loop and WaitForSingleObject / WaitForMulitipleObjects.  You 
can even specify a timeout in the WaitXXX calls so that B wakes 
periodically, even if there are nothing signaled.  When the WaitXXX function 
returns, you can check for the existence of the file.

Regards,
Dennis.

--------------------------------------------------
From: "John Bird" <johnkbird at paradise.net.nz>
Sent: Wednesday, August 18, 2010 4:43 PM
To: "NZ Borland Developers Group - Delphi List" <delphi at delphi.org.nz>
Subject: [DUG]  Sending notification between programs

> Which way would you favour to do the following ?
>
> I have two Delphi programs (A and B) that I will pass data from A to B - I 
> will probably use  a file to put the data in because its quite structured. 
> B will sleep on a timer loop until this something is triggered.
>
> What I want to do is send a simple notification from program A to B that 
> there is something to do - i.e. trigger an event in B to wake and do 
> something to process this.
>
> There are various ways I could communicate this notification
>
> 1 - Has to add minimal overhead of size and processing to programs A and B
> 2 - A can tolerate B not responding immediately without freezing but 
> preferably will know
>
> The ways I have considered to be candidates are
>
> a - Windows messaging
> b - TCP/IP Indy   (which could send the data too.  (adds complexity of 
> needs to be done in a thread to not affect the main program A)
> c - make program B a DLL
> d - Roll my own - make a timer in B which polls for for some condition and 
> otherwise continues to sleep
> e - something else.
>
> Kindly share your favoured options how you might do this.
>
> John



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