TIMER_CREATE(2FREEBSD) - Linux man page online | System calls

Create a per-process timer (REALTIME).

July 15, 2016


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 ref‐ erenced 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 particu‐ lar clock, clock_id, is defined in <time.h>. The timer whose ID is returned is in a dis‐ armed 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 unspeci‐ fied 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 indi‐ cate the error. The value of timerid is undefined if an error occurs.


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.


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.
BSD July 15, 2016 BSD
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timer_create(2freebsd) referred by
refer to clock_getres(2) | timer_create(2) | timer_delete(2) | timer_getoverrun(2)
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