Re: after ids

On 7/6/08, Daniel A. Steffen <das@...> wrote:
>
> All the implementations of relative timers in the OS (nanosleep(),
> pthread_cond_timedwait_relative_np() etc) are based on this reference.

So, the shell loop 'while :;do sleep 1;echo foo;done' should have
visible quirks when someone sets the date, right ?

Is the timeout in select() also based on this absolute clock ?

> Finding a function that returns an monotonic time reference on a
> system does not solve the problem of implementing relative timers in
> Tcl however, you also need a way for the notifier to wait for a
> relative time interval, e.g. the current threaded unix notifier
> waiting is based on pthread_cond_timedwait(), which uses absolute time
> (c.f. Tcl_ConditionWait()).

That may be another reason to reform the threaded notifier, if you
allow me that digression 

> Darwin has pthread_cond_timedwait_relative_np() for exactly this
> purpose, I don't know if other systems have something equivalent.

Don't know either but please notice that going to select() everywhere
would solve the problem uniformly. The non-threaded unix notifer has
no problem with relative timers, it's just that currently the value is
recomputed based on absolute time when it needs be.

> (converting next absolute timer fire to a relative
> time interval may result in waiting for too long if there are changes
> to the gettod base).

That's exactly what happens today in Windows and unthreaded unix,
since WaitForMultiple* (resp. select()) both take a relative timeout.
See TIP302.

-Alex

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