20 ms would be a time slice (timer tick). But threads not have to switch at
only timer ticks. A higher priority thread gets CPU as soon as it becomes
Ah, thanks.
I'm not sure how the OS times switching threads, but it seems much faster
than 20ms. I regularly use multiple threads that wake on 20ms intervals
and it's pretty consistent, even on single CPU machines.
I suppose it's consistent because most threads in the system are waiting
most of the time.
Mark
--
Mark Salsbery
Microsoft MVP - Visual C++
"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp> wrote in message
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"Mark Salsbery [MVP]" <MarkSalsbery[MVP]@newsgroup.nospam> wrote in
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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
The system timer interrupt interval is available from
GetSystemTimeAdjustment(). If my memory is right it was 20 msec for
NT/2K/XP. On my Vista machine it returns 15 msec.
Timer-based thread switching can't go faster than the system timer. But
who knows, with multimedia I/O they may have souped it up to do a thread
switch upon a multimedia interrupt. Sound cards don't need much help
though, because they contain hardware buffering that greatly reduces the
interrupt rate.
--
Scott McPhillips [VC++ MVP]