Re: Time measurement problem during task switching

"Alex Blekhman" <>
Fri, 4 Jul 2008 14:08:47 +0300
"Simone Navari" wrote:

I written a DLL to interface with a custom PCI device;
manufacturer provides me via another DLL some functions to write
and read bytes to device and some other to know if board is
ready to accept or send data.

How does it signal the change of state? Usually HW SDK's provide
you with a handle to a kernel object [device/file/event/etc.] that
you can wait on.

What I need is to implement a timeout mechanism when my DLL has
to wait for some data, I've used timeGetTime function to measure
elapsed time from waiting start but if some other heavy
processes are running seems that my waiting routine is
interrupted and when scheduler gives me the control again a time
greater than timeout is elapsed so I return with an error.

Windows is not real-time OS. It is close to impossible to get
exact timings on Windows due to preemptive multitasking.
Theoretically you could use Waitable Timer object in a thread with
high priority, so you will have less chances to be interrupted.
But no object will guarantee you exact periods in user mode code.


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