Re: Add pselect, ppoll system calls.

["Mattias Engdegård" <mattias@virtutech.se>]

>Monotonic clocks are guaranteed to not go backward. A sudden warp 35
>seconds into the future when you have timers set for 15 and 20
>seconds into the future is still ugly....

I don't have the POSIX specs handy, but I see no reason we could not let
it use a warpless monotonic clock.

The problem of timeouts going wild when time is being warped applies
to syscalls using relative timeouts as well. Even when a relative
timeout is wanted, it is usually transformed (via gettimeofday or
similar) to an absolute timeout:

   T = some_clock() + dT
   timeout = dT
   loop:
      poll(..., timeout)
      if (poll did not time out):
          now = some_clock()
          timeout = MAX(0, T - now)
          goto loop

This kind of code is very common, because the timeout is usually the
time to some event in the future. If some_clock() is subject to
warping (which is the case when gettimeofday() is used), then you have
the problem again.