Yawn

[oex]

What does the 'Sleep' function actually do?


Edit: I know what the result is but what does it do on an OS level to stop execution....

[dedndave]

here is my understanding of it
besides "waiting" the specified time-period, it relinquishes the remainder of the current time-slice
this allows some other process/thread(s) to execute
when execution returns to the calling thread, it will be at the beginning of a new time-slice
it can be used to prevent lock-up

[oex]

So it efectively runs SetPriorityClass IDLE_PRIORITY_CLASS or somesuch? Only it considers System Idle Process as a running process....

And btw if you dont have power saving I take it System Idle Process is just a loop?

[Farabi]

So it efectively runs SetPriorityClass IDLE_PRIORITY_CLASS or somesuch? Only it considers System Idle Process as a running process....

And btw if you dont have power saving I take it System Idle Process is just a loop?

It will be usefull if you create a new thread, it will save the CPU usage on the loop.

[qWord]

I think that the thread is removed from task schedulers thread/task chain until the requested time has past - so it is simply not execute.

[MichaelW]

I think for anything greater than a Sleep(0) the system effectively suspends the calling thread.

[oex]

Interesting ty all.... This answers my underlying question that the Sleep function is probably the lowest level I should go without interfering with windows management although I'll have to dig into the last 2 posts a little further to be sure....

[Slugsnack]

You can try looking into ZwDelayExecution() in ntdll.dll

[qWord]

You can try looking into ZwDelayExecution() in ntdll.dll

using an kernel debugger he can  :bg

[donkey]

This is how I see the function...

The system first creates an activation context for a waitable timer (all global objects require an actctx) then that timer object sets up a spinlock that is outside of the calling process in kernel mode. The spinlock simply monitors the clock and is set to the signalled state when the timer expires. In the mean time the thread is suspended by removing its entry from the context switch list (it is Zombified), it is reinserted after the spinlock exits and the temporary ActCtx is released, this allows its time slice to be used by other processes. The advantage to making the timer a global object and running it independent of the calling process is obvious, it allows for the complete suspension of the calling thread, something that is not possible if you replace it with your own code, this is true of all waitable objects. You can mimic the behavior of Sleep by setting up a waitable timer and calling WaitForSingleObject, though the execution path is slightly different the effect is the same.