clocks(2)

NAME

clock_settime(), clock_gettime(), clock_getres() — clock operations

SYNOPSIS

#include <time.h> 

int clock_settime( 
     clockid_t clock_id, 
     const struct timespec *tp); 

int clock_gettime( 
     clockid_t clock_id, 
     struct timespec *tp); 

int clock_getres( 
     clockid_t clock_id, 
     struct timespec *res); 

DESCRIPTION

clock_settime()

The clock_settime() function sets the specified clock, clock_id, to the value specified by tp. Time values that are between two consecutive non-negative integer multiples of the resolution of the specified clock are truncated down to the smaller multiple of the resolution.

clock_gettime()

The clock_gettime() function returns the current value tp for the specified clock, clock_id.

clock_getres()

The resolution of any clock can be obtained by calling clock_getres(). Clock resolutions are implementation defined and are not settable by a process. If the argument res is not NULL, the resolution of the specified clock is stored into the location pointed to by res. If res is NULL, the clock resolution is not returned.

A clock may be system wide, that is, visible to all processes; or per-process, measuring time that is meaningful only within a process.

The following clocks are supported:

CLOCK_REALTIME: This clock represents the realtime clock for the system. For this clock, the values returned by clock_gettime() and specified by clock_settime() represent the amount of time (in seconds and nanoseconds) since the Epoch. It is a system wide clock. The SYSATTR privilege is required to set this clock. Processes owned by the superuser have this privilege. Processes owned by other users may have this privilege, depending on system configuration. See privileges(5) for more information about privileged access on systems that support fine-grained privileges.
CLOCK_VIRTUAL: This clock represents the amount of time (in seconds and nanoseconds) that the calling process has spent executing code in the user's context. It is a per-process clock. It cannot be set by the user.
CLOCK_PROFILE: This clock represents the amount of time (in seconds and nanoseconds) that the calling process has spent executing code in both the user's context and in the operating system on behalf of the calling process. It is a per-process clock. It cannot be set by the user.
RTTIMER0 RTTIMER1: These clocks are high resolution hardware clocks present on HP-RT realtime systems. It is included here so that applications accessing this hardware can be compiled on HP-UX systems and then ported to an HP-RT target. HP-UX does not support RTTIMER0 or RTTIMER1.

RETURN VALUE

A return of zero indicates that the call succeeded. A return value of -1 indicates that an error occurred, and errno is set to indicate the error.

ERRORS

If any of the following conditions occur, the clock_settime(), clock_gettime(), and clock_getres() functions return -1 and set errno (see errno(2)) to the corresponding value:

ENOSYS: The functions clock_settime(), clock_gettime(), and clock_getres() are not supported by this implementation.
EINVAL: The clock_id argument does not specify a known clock.
EINVAL: The tp argument to clock_settime() is outside the range for the given clock_id.
EINVAL: The tp argument specified a nanosecond value less than zero or greater than or equal to 1000 million.
EPERM: The requesting process does not have the necessary privileges to set the specified clock.
EFAULT: The tp or res argument points to an invalid address.

EXAMPLES

Advance the system wide realtime clock approximately one hour:

#include <time.h> 
#include <errno.h> 

struct timespec cur_time, new_time; 

if (clock_gettime(CLOCK_REALTIME, &cur_time)) { 
     perror("clock_gettime(CLOCK_REALTIME) failed"); 
     exit(1); 
} 
new_time.tv_sec = cur_time.tv_sec + 3600; 
new_time.tv_nsec = cur_time.tv_nsec; 
if (clock_settime(CLOCK_REALTIME, &new_time)) { 
     perror("clock_settime(CLOCK_REALTIME) failed"); 
     exit(2); 
} 

Get the resolution of the user profiling clock:

#include <time.h> 
#include <errno.h> 

struct timespec resolution; 

if (clock_getres(CLOCK_PROFILE, &resolution)) { 
     perror("clock_getres(CLOCK_PROFILE) failed"); 
     exit(1); 
} 
(void)printf("Resolution of user profiling clock is:\n"); 
(void)printf("%d seconds and %d nanoseconds.\n", 
          resolution.tv_sec, resolution.tv_nsec); 

AUTHOR

clock_settime(), clock_gettime(), and clock_getres() were derived from the proposed IEEE POSIX P1003.4 Standard, Draft 14.

STANDARDS CONFORMANCE

clock_getres(): POSIX.4

clock_gettime(): POSIX.4

clock_settime(): POSIX.4