Re: Put thread in sleep mode

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>
Sat, 11 Aug 2007 08:33:28 -0400
MiG wrote:

I guess that's as good as it gets. Going for a real-time OS, as someone
suggested above, isn't an alternative for me, as this project must be
developed for Windows exclusively. I guess I thought there were API
calls for the sort of precision I need.

Having read the descriptions for the set of WaitFor<xxxx> functions on
MSDN, it seems to me that these functions imply the existence of (at
least) another thread that issues the calls, meaning a thread can't wait
for itself. Or _can it_?

SetWaitableTimer seems to be the best option for what I need to do, as
it seems to allow a thread to schedule its own inactivity time.

Lastly, how accurate are these timers? Assuming that the system a given
program is running on has enough available RAM, there are no resource
intensive applications running and the processor is fast enough, how
much is the Windows thread scheduler likely to drift away from the
requested thread inactivity waiting period?

Many thanks to all the posters for their comments and suggestions. It is
much appreciated.

The WaitFor... functions are usually used to wait for signal from either
the operating system or other threads. But their timeout parameter also
lets them be used like Sleep.

The internal clock resolution used for all kinds of timing is only 20
msec or so. The multimedia functions already mentioned can change this
to 1 msed at best.

But the biggest problem is that a Windows program will be suspended for
indeterminate periods when the os needs to do something else. It is
very hard to minimize "something else" - Windows has its own priorities
and agenda.

You best defense in a time-critical thread is SetThreadPriority. Higher
thread priority will reduce the number of arbitrary suspensions (but no
eliminate them). The best performance you can get is indicated by
graphic game programs: maybe 30-40 frames per second, but with some

Scott McPhillips [MVP VC++]

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