[DUG] Sending notification between programs

[John Bird]

The property
FILE_NOTIFY_CHANGE_LAST_WRITE

looks like a possibility, as if structured data has just been written to a 
file this event should be triggered.   The only gotcha seems to be that the 
better the caching is the less likely the event will fire - according to the 
help.  Tricky.

John

>
> 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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