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Document all CLOCK_* values 

The manual documents CLOCK_REALTIME and CLOCK_MONOTONIC but not other
CLOCK_* values.  Add documentation of the POSIX clocks
CLOCK_PROCESS_CPUTIME_ID and CLOCK_THREAD_CPUTIME_ID, along with a
reference to the Linux man pages for the semantics of the
Linux-specific clocks supported (as with some other functionality
coming direct from the Linux kernel where the man pages can be
considered the main documentation).

Note: CLOCK_MONOTONIC_RAW, CLOCK_REALTIME_COARSE and
CLOCK_MONOTONIC_COARSE are also defined in the toplevel bits/time.h,
as used for Hurd.  Nevertheless, I see no sign that the Hurd code in
glibc actually has any support for those clocks, so I think it is
correct to document them as Linux-specific (and to refer only to the
Linux man pages for their semantics).

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Joseph Myers 2025-05-12 14:56:07 +00:00
parent eff1f680cf
commit f451a02a8c
1 changed files with 30 additions and 1 deletions
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31
manual/time.texi
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@ -529,7 +529,36 @@ Therefore, @code{CLOCK_MONOTONIC} cannot be used to measure
absolute time, only elapsed time.
@end deftypevr
Systems may support more than just these two POSIX clocks.
The following clocks are defined by POSIX, but may not be supported by
all POSIX systems:
@deftypevr Macro clockid_t CLOCK_PROCESS_CPUTIME_ID
@standards{POSIX.1, time.h}
This POSIX clock measures the amount of CPU time used by the calling
process.
@end deftypevr
@deftypevr Macro clockid_t CLOCK_THREAD_CPUTIME_ID
@standards{POSIX.1, time.h}
This POSIX clock measures the amount of CPU time used by the calling
thread.
@end deftypevr
The following clocks are Linux extensions:
@deftypevr Macro clockid_t CLOCK_MONOTONIC_RAW
@deftypevrx Macro clockid_t CLOCK_REALTIME_COARSE
@deftypevrx Macro clockid_t CLOCK_MONOTONIC_COARSE
@deftypevrx Macro clockid_t CLOCK_BOOTTIME
@deftypevrx Macro clockid_t CLOCK_REALTIME_ALARM
@deftypevrx Macro clockid_t CLOCK_BOOTTIME_ALARM
@deftypevrx Macro clockid_t CLOCK_TAI
@standards{Linux, time.h}
For details of these clocks, see the manual page
@manpageurl{clock_gettime,2}.
@end deftypevr
Systems may support additional clocks beyond those listed here.
@deftypefun int clock_gettime (clockid_t @var{clock}, struct timespec *@var{ts})
@standards{POSIX.1, time.h}