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


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


     #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


     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  itimer-
     spec 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
     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  speci-
     fying  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 speci-
     fied 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  inter-
     val,  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.


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


     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.


     These system calls are available since Linux 2.6.


     POSIX.1-2001, POSIX.1-2008.


     See timer_create(2).


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


     This page is part of release 4.16 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

Linux 2017-09-15 TIMER_SETTIME(2)

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