NAME

     timer_create — create a per-process timer (REALTIME)

LIBRARY

     POSIX Real-time Library (librt, -lrt)

SYNOPSIS

     #include <time.h>
     #include <signal.h>

     int
     timer_create(clockid_t clockid, struct sigevent *restrict evp, timer_t *restrict timerid);

DESCRIPTION

     The timer_create() system call creates a per-process timer using the specified clock,
     clock_id, as the timing base.  The timer_create() system call returns, in the location
     referenced by timerid, a timer ID of type timer_t used to identify the timer in timer
     requests.  This timer ID is unique within the calling process until the timer is deleted.
     The particular clock, clock_id, is defined in <time.h>.  The timer whose ID is returned is
     in a disarmed state upon return from timer_create().

     The evp argument, if non-NULL, points to a sigevent structure.  This structure, allocated by
     the application, defines the asynchronous notification to occur when the timer expires.

     If evp->sigev_notify is SIGEV_SIGNO or SIGEV_THREAD_ID, the signal specified in
     evp->sigev_signo will be sent to the calling process (SIGEV_SIGNO) or to the thread whose
     LWP ID is evp->sigev_notify_thread_id (SIGEV_THREAD_ID).  The information for the queued
     signal will include:

     Member      Value
     si_code     SI_TIMER
     si_value    the value stored in evp->sigev_value
     si_timerid  timer ID
     si_overrun  timer overrun count
     si_errno    If timer overrun is {DELAYTIMER_MAX}, an error code defined in <errno.h>

     If the evp argument is NULL, the effect is as if the evp argument pointed to a sigevent
     structure with the sigev_notify member having the value SIGEV_SIGNAL, the sigev_signo having
     a default signal number (SIGALRM), and the sigev_value member having the value of the timer
     ID.

     This implementation supports a clock_id of CLOCK_REALTIME or CLOCK_MONOTONIC.

     If evp->sigev_notify is SIGEV_THREAD and sev->sigev_notify_attributes is not NULL, if the
     attribute pointed to by sev->sigev_notify_attributes has a thread stack address specified by
     a call to pthread_attr_setstack() or pthread_attr_setstackaddr(), the results are
     unspecified if the signal is generated more than once.

RETURN VALUES

     If the call succeeds, timer_create() returns zero and updates the location referenced by
     timerid to a timer_t, which can be passed to the per-process timer calls.  If an error
     occurs, the system call returns a value of -1 and the global variable errno is set to
     indicate the error.  The value of timerid is undefined if an error occurs.

ERRORS

     The timer_create() system call will fail if:

     [EAGAIN]           The calling process has already created all of the timers it is allowed
                        by this implementation.

     [EINVAL]           The specified clock ID is not supported.

     [EINVAL]           The specified asynchronous notification method is not supported.

     [EFAULT]           Any arguments point outside the allocated address space or there is a
                        memory protection fault.

SEE ALSO

     clock_getres(2), timer_delete(2), timer_getoverrun(2), sigevent(3), siginfo(3)

STANDARDS

     The timer_create() system call conforms to IEEE Std 1003.1-2004 (“POSIX.1”).

HISTORY

     Support for POSIX per-process timer first appeared in FreeBSD 7.0.