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Fast interapp communication

Posted on 2004-10-20
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Last Modified: 2010-08-05
For somewhat arcane reasons, I need to monitor (globally) keystrokes and mouse movements and later analyze that data.

OK, I can do system wide hooks (ordinary or low level) and accumulate the data in the hookprocs.

But I need to send that data, periodically, to a separate analysis app running in the system tray. This has to be done fast because of the performance implications for the system as a whole. I was thinking WM_COPYDATA but the SDK says to use SendMessage .. I would rather use PostMessage (can I do this??)

Now, maybe I am getting confused here, but is there any reason I cannot grab some memory in the hookproc with GlobalAlloc send its address to the analysis app and free it there?

The data to be transferred is maybe 5K bytes max, if that makes a difference
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Question by:Mutley2003
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Wim ten Brink earned 2000 total points
ID: 12355877
Use a memory mapped file, that is shared between the keylogger and the analyzer. The keylogger writes and the analyzer just reads. Two 64-bits integers (read/write pointer) at the beginning of the MMF should indicate the current position that they are reading and the rest of the MMF is to store the data in a round-robin style. (Thus, when you get past the end of the file, you start at the beginning again.)
A MMF doesn't have to be a physical file even. It can just be a reserved part of memory that is shared between applications. All you have to remember is that you should never read or write beyong the filesize. Also, never write beyond the read-pointer and never read beyond the write pointer. If the read-pointer is 0 then the write pointer knows there's no reader and thus it might not even need to write anything...

MMF's can be reasonable big in size, so a size of 5 to 10 MB is quite well possible.
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by:Mutley2003
ID: 12356062
ok, cool
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