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TIMER_CREATE(2) System Calls Manual TIMER_CREATE(2)


timer_createcreate a per-process timer (REALTIME)


POSIX Real-time Library (librt, -lrt)


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

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


The () 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:

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 () or (), 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 Debian