Re: Winsock select timeout
"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp> wrote in message
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<vanisathish@gmail.com> wrote in message
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but the thread switching period is probably 20 milliseconds.
Hi Scott,
I'm curious, where did you get that number from? That seems like a really
long time and it makes me wonder how my multimedia software works at all :)
Is it really that long?
Cheers,
Mark
--
Mark Salsbery
Microsoft MVP - Visual C++
"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp> wrote in message
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<vanisathish@gmail.com> wrote in message
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Hi,
i'm communicating with more than 40 serial devices connected thru' an
serial hub. the pc has to communicate thru' UDP to the serial hub.
since the response is quite sensitve, ( the application has to timeout
within 100msec) we are using "select" call with timeout.
There are around 100 threads that are parallely polling all the 40
devices on the serial hub.
I noticed that the select call is timingout i.e. returning 0
eventhough there is socket in the buffer..does this mean that the
timer got expired when that thread is in the sleep state (i.e. some
other thread is running) and later when the thread resumes, it is just
returning the previous state...
I'm running this application on a 2.66G Pentium PC..will the context
switching be an issue at all here. i dont see this problem if the
number of threads is reduced...,meaning less context switching.
thanks
It is hard to be sure without understanding more about your program, but
the thread switching period is probably 20 milliseconds. So if you have
100 threads it could be as long as 2000 msec before each one gets a turn.
So of course a 100 msec timeout seems likely to fail. The fact that the
problem seems to go away with fewer threads supports this theory. This
sounds like a serious design scalability problem.
Since all the UDP messages come from the same place they must be
sequential, and you could consider a design that uses only one thread to
process all UDP input.
--
Scott McPhillips [VC++ MVP]