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Man Pages
TIMER_CREATE(2) FreeBSD System Calls Manual TIMER_CREATE(2)

timer_create
create a per-process timer (REALTIME)

POSIX Real-time Library (librt, -lrt)

#include <time.h>
#include <signal.h>
int
timer_create(clockid_t clockid, struct sigevent *restrict evp, timer_t *restrict timerid);

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_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.

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.

The timer_create() system call will fail if:
[]
The calling process has already created all of the timers it is allowed by this implementation.
[]
The specified clock ID is not supported.
[]
The specified asynchronous notification method is not supported.
[]
Any arguments point outside the allocated address space or there is a memory protection fault.

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

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

Support for POSIX per-process timer first appeared in FreeBSD 7.0.
July 15, 2016 FreeBSD 12.0-RELEASE

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