[v4,12/12] nptl: Remove futex_supports_exact_relative_timeouts

  The only implementation of futex_supports_exact_relative_timeouts always
returns true. Let's remove it and all its callers.

* nptl/pthread_cond_wait.c: (__pthread_cond_clockwait): Remove code that is
  only useful if futex_supports_exact_relative_timeouts () returns false.

* nptl/pthread_condattr_setclock.c: (pthread_condattr_setclock): Likewise.

* sysdeps/nptl/futex-internal.h: Remove comment about relative timeouts
  potentially being imprecise since it's no longer true. Remove declaration
  of futex_supports_exact_relative_timeouts.

* sysdeps/unix/sysv/linux/futex-internal.h: Remove implementation of
  futex_supports_exact_relative_timeouts.
---
 ChangeLog                                | 13 +++++++++++++
 nptl/pthread_cond_wait.c                 |  5 -----
 nptl/pthread_condattr_setclock.c         |  5 -----
 sysdeps/nptl/futex-internal.h            |  9 +--------
 sysdeps/unix/sysv/linux/futex-internal.h |  8 --------
 5 files changed, 14 insertions(+), 26 deletions(-)
  

On 18/06/2019 13:33, Mike Crowe wrote:
> The only implementation of futex_supports_exact_relative_timeouts always
> returns true. Let's remove it and all its callers.

LGTM.

> 
> * nptl/pthread_cond_wait.c: (__pthread_cond_clockwait): Remove code that is
>   only useful if futex_supports_exact_relative_timeouts () returns false.
> 
> * nptl/pthread_condattr_setclock.c: (pthread_condattr_setclock): Likewise.
> 
> * sysdeps/nptl/futex-internal.h: Remove comment about relative timeouts
>   potentially being imprecise since it's no longer true. Remove declaration
>   of futex_supports_exact_relative_timeouts.
> 
> * sysdeps/unix/sysv/linux/futex-internal.h: Remove implementation of
>   futex_supports_exact_relative_timeouts.

Ok.

> ---
>  ChangeLog                                | 13 +++++++++++++
>  nptl/pthread_cond_wait.c                 |  5 -----
>  nptl/pthread_condattr_setclock.c         |  5 -----
>  sysdeps/nptl/futex-internal.h            |  9 +--------
>  sysdeps/unix/sysv/linux/futex-internal.h |  8 --------
>  5 files changed, 14 insertions(+), 26 deletions(-)
> 
> diff --git a/ChangeLog b/ChangeLog
> index 984275c..cf07e4d 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -1,3 +1,16 @@
> +2019-06-18  Mike Crowe  <mac@mcrowe.com>
> +
> +	* nptl/pthread_cond_wait.c: (__pthread_cond_clockwait): Remove code
> +	that is only useful if futex_supports_exact_relative_timeouts ()
> +	returns false.
> +	* nptl/pthread_condattr_setclock.c: (pthread_condattr_setclock):
> +	Likewise.
> +	* sysdeps/nptl/futex-internal.h: Remove comment about relative
> +	timeouts potentially being imprecise since it's no longer true.
> +	Remove declaration of futex_supports_exact_relative_timeouts.
> +	* sysdeps/unix/sysv/linux/futex-internal.h: Remove implementation
> +	of futex_supports_exact_relative_timeouts.
> +
>  2019-05-27  Mike Crowe  <mac@mcrowe.com>
>  
>  	* NEWS: Mention recently-added pthread_cond_clockwait,
> diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
> index 558f930..cd98f50 100644
> --- a/nptl/pthread_cond_wait.c
> +++ b/nptl/pthread_cond_wait.c
> @@ -670,11 +670,6 @@ __pthread_cond_clockwait (pthread_cond_t *cond, pthread_mutex_t *mutex,
>    if (!futex_abstimed_supported_clockid (clockid))
>      return EINVAL;
>  
> -  /* If we do not support waiting using CLOCK_MONOTONIC, return an error.  */
> -  if (clockid == CLOCK_MONOTONIC
> -      && !futex_supports_exact_relative_timeouts ())
> -    return EINVAL;
> -
>    return __pthread_cond_wait_common (cond, mutex, clockid, abstime);
>  }
>  

Ok.

> diff --git a/nptl/pthread_condattr_setclock.c b/nptl/pthread_condattr_setclock.c
> index 641a041..ac91923 100644
> --- a/nptl/pthread_condattr_setclock.c
> +++ b/nptl/pthread_condattr_setclock.c
> @@ -33,11 +33,6 @@ pthread_condattr_setclock (pthread_condattr_t *attr, clockid_t clock_id)
>         in the pthread_cond_t structure needs to be adjusted.  */
>      return EINVAL;
>  
> -  /* If we do not support waiting using CLOCK_MONOTONIC, return an error.  */
> -  if (clock_id == CLOCK_MONOTONIC
> -      && !futex_supports_exact_relative_timeouts())
> -    return ENOTSUP;
> -
>    /* Make sure the value fits in the bits we reserved.  */
>    assert (clock_id < (1 << COND_CLOCK_BITS));
>  


Ok.

> diff --git a/sysdeps/nptl/futex-internal.h b/sysdeps/nptl/futex-internal.h
> index bc29bdb..9baae38 100644
> --- a/sysdeps/nptl/futex-internal.h
> +++ b/sysdeps/nptl/futex-internal.h
> @@ -51,8 +51,7 @@
>     Both absolute and relative timeouts can be used.  An absolute timeout
>     expires when the given specific point in time on the specified clock
>     passes, or when it already has passed.  A relative timeout expires when
> -   the given duration of time on the CLOCK_MONOTONIC clock passes.  Relative
> -   timeouts may be imprecise (see futex_supports_exact_relative_timeouts).
> +   the given duration of time on the CLOCK_MONOTONIC clock passes.
>  
>     Due to POSIX requirements on when synchronization data structures such
>     as mutexes or semaphores can be destroyed and due to the futex design
> @@ -81,12 +80,6 @@
>  static __always_inline int
>  futex_supports_pshared (int pshared);
>  
> -/* Returns true if relative timeouts are robust to concurrent changes to the
> -   system clock.  If this returns false, relative timeouts can still be used
> -   but might be effectively longer or shorter than requested.  */
> -static __always_inline bool
> -futex_supports_exact_relative_timeouts (void);
> -
>  /* Atomically wrt other futex operations on the same futex, this blocks iff
>     the value *FUTEX_WORD matches the expected value.  This is
>     semantically equivalent to:

Ok.

> diff --git a/sysdeps/unix/sysv/linux/futex-internal.h b/sysdeps/unix/sysv/linux/futex-internal.h
> index 03312d6..30707e7 100644
> --- a/sysdeps/unix/sysv/linux/futex-internal.h
> +++ b/sysdeps/unix/sysv/linux/futex-internal.h
> @@ -46,14 +46,6 @@ futex_supports_pshared (int pshared)
>      return EINVAL;
>  }
>  
> -/* The Linux kernel supports relative timeouts measured against the
> -   CLOCK_MONOTONIC clock.  */
> -static __always_inline bool
> -futex_supports_exact_relative_timeouts (void)
> -{
> -  return true;
> -}
> -
>  /* See sysdeps/nptl/futex-internal.h for details.  */
>  static __always_inline int
>  futex_wait (unsigned int *futex_word, unsigned int expected, int private)
> 

Ok.