[PATCH v2] Semaphores: add sem_clockwait GNU extension [BZ #14717]

[Ben Hutchings]

On Fri, 2018-12-14 at 22:20 +0100, Jan Klötzke wrote:
> As defined by POSIX.1-2001 the 'abstime' timeout of  sem_timedwait()
> shall be based on CLOCK_REALTIME. This has the unpleasant effect that
> application timeouts are affected by system clock adjustments.
> 
> The added sem_clockwait() function behaves just like sem_timedwait() but
> lets the user specify the clock against which the timeout is measured.
> The implementation is based on [1] which covers all functions that take an
> absolute struct timespec timeout.
[...]
> --- /dev/null
> +++ b/nptl/sem_clockwait.c
> @@ -0,0 +1,52 @@
[...]
> +int
> +sem_clockwait (sem_t *sem, clockid_t clock_id, const struct timespec *abstime)
> +{
> +  if (__glibc_unlikely (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000))
> +    {
> +      __set_errno (EINVAL);
> +      return -1;
> +    }
> +
> +  if (__glibc_unlikely (clock_id != CLOCK_MONOTONIC
> +                       && clock_id != CLOCK_REALTIME))
> +    {
> +      __set_errno (EINVAL);
> +      return -1;
> +    }
> +
> +  /* If we do not support waiting using CLOCK_MONOTONIC, return an error.  */
> +  if (clock_id == CLOCK_MONOTONIC
> +      && !futex_supports_exact_relative_timeouts())
> +    return ENOTSUP;
[...]

Returning an error code here is inconsistent with sem_timedwait() (and
even with the other error cases).

Ben.

-- 
Ben Hutchings, Software Developer                Â         Codethink Ltd
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