timer_gettime

TIMER_SETTIME(2)           Linux Programmer's Manual          TIMER_SETTIME(2)



NAME
       timer_settime, timer_gettime - arm/disarm and fetch state of POSIX per-
       process timer

SYNOPSIS
       #include <time.h>

       int timer_settime(timer_t timerid, int flags,
                         const struct itimerspec *new_value,
                         struct itimerspec *old_value);
       int timer_gettime(timer_t timerid, struct itimerspec *curr_value);

       Link with -lrt.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       timer_settime(), timer_gettime(): _POSIX_C_SOURCE >= 199309L

DESCRIPTION
       timer_settime() arms or disarms the timer identified by timerid.  The
       new_value argument is pointer to an itimerspec structure that specifies
       the new initial value and the new interval for the timer.  The
       itimerspec structure is defined as follows:

           struct timespec {
               time_t tv_sec;                /* Seconds */
               long   tv_nsec;               /* Nanoseconds */
           };

           struct itimerspec {
               struct timespec it_interval;  /* Timer interval */
               struct timespec it_value;     /* Initial expiration */
           };

       Each of the substructures of the itimerspec structure is a timespec
       structure that allows a time value to be specified in seconds and
       nanoseconds.  These time values are measured according to the clock
       that was specified when the timer was created by timer_create(2).

       If new_value->it_value specifies a nonzero value (i.e., either subfield
       is nonzero), then timer_settime() arms (starts) the timer, setting it
       to initially expire at the given time.  (If the timer was already
       armed, then the previous settings are overwritten.)  If
       new_value->it_value specifies a zero value (i.e., both subfields are
       zero), then the timer is disarmed.

       The new_value->it_interval field specifies the period of the timer, in
       seconds and nanoseconds.  If this field is nonzero, then each time that
       an armed timer expires, the timer is reloaded from the value specified
       in new_value->it_interval.  If new_value->it_interval specifies a zero
       value, then the timer expires just once, at the time specified by
       it_value.

       By default, the initial expiration time specified in
       new_value->it_value is interpreted relative to the current time on the
       timer's clock at the time of the call.  This can be modified by
       specifying TIMER_ABSTIME in flags, in which case new_value->it_value is
       interpreted as an absolute value as measured on the timer's clock; that
       is, the timer will expire when the clock value reaches the value
       specified by new_value->it_value.  If the specified absolute time has
       already passed, then the timer expires immediately, and the overrun
       count (see timer_getoverrun(2)) will be set correctly.

       If the value of the CLOCK_REALTIME clock is adjusted while an absolute
       timer based on that clock is armed, then the expiration of the timer
       will be appropriately adjusted.  Adjustments to the CLOCK_REALTIME
       clock have no effect on relative timers based on that clock.

       If old_value is not NULL, then it points to a buffer that is used to
       return the previous interval of the timer (in old_value->it_interval)
       and the amount of time until the timer would previously have next
       expired (in old_value->it_value).

       timer_gettime() returns the time until next expiration, and the
       interval, for the timer specified by timerid, in the buffer pointed to
       by curr_value.  The time remaining until the next timer expiration is
       returned in curr_value->it_value; this is always a relative value,
       regardless of whether the TIMER_ABSTIME flag was used when arming the
       timer.  If the value returned in curr_value->it_value is zero, then the
       timer is currently disarmed.  The timer interval is returned in
       curr_value->it_interval.  If the value returned in
       curr_value->it_interval is zero, then this is a "one-shot" timer.

RETURN VALUE
       On success, timer_settime() and timer_gettime() return 0.  On error, -1
       is returned, and errno is set to indicate the error.

ERRORS
       These functions may fail with the following errors:

       EFAULT new_value, old_value, or curr_value is not a valid pointer.

       EINVAL timerid is invalid.

       timer_settime() may fail with the following errors:

       EINVAL new_value.it_value is negative; or new_value.it_value.tv_nsec is
              negative or greater than 999,999,999.

VERSIONS
       These system calls are available since Linux 2.6.

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

EXAMPLE
       See timer_create(2).

SEE ALSO
       timer_create(2), timer_getoverrun(2), time(7)

COLOPHON
       This page is part of release 5.03 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.




Linux                             2017-09-15                  TIMER_SETTIME(2)