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NAME

     timer_getoverrun, timer_gettime, timer_settime - per-process timers
     (REALTIME)

LIBRARY

     library “librt”

SYNOPSIS

     #include <time.h>

     int
     timer_getoverrun(timer_t timerid);

     int
     timer_gettime(timer_t timerid, struct itimerspec *value);

     int
     timer_settime(timer_t timerid, int flags,
             const struct itimerspec *restrict value,
             struct itimerspec *restrict ovalue);

DESCRIPTION

     The timer_gettime() system call stores the amount of time until the
     specified timer, timerid, expires and the reload value of the timer into
     the space pointed to by the value argument.  The it_value member of this
     structure contains the amount of time before the timer expires, or zero
     if the timer is disarmed.  This value is returned as the interval until
     timer expiration, even if the timer was armed with absolute time.  The
     it_interval member of value contains the reload value last set by
     timer_settime().

     The timer_settime() system call sets the time until the next expiration
     of the timer specified by timerid from the it_value member of the value
     argument and arms the timer if the it_value member of value is non-zero.
     If the specified timer was already armed when timer_settime() is called,
     this call resets the time until next expiration to the value specified.
     If the it_value member of value is zero, the timer is disarmed.  If the
     timer is disarmed, then pending signal is removed.

     If the flag TIMER_ABSTIME is not set in the argument flags,
     timer_settime() behaves as if the time until next expiration is set to be
     equal to the interval specified by the it_value member of value.  That
     is, the timer expires in it_value nanoseconds from when the call is made.
     If the flag TIMER_ABSTIME is set in the argument flags, timer_settime()
     behaves as if the time until next expiration is set to be equal to the
     difference between the absolute time specified by the it_value member of
     value and the current value of the clock associated with timerid.  That
     is, the timer expires when the clock reaches the value specified by the
     it_value member of value.  If the specified time has already passed, the
     system call succeeds and the expiration notification is made.

     The reload value of the timer is set to the value specified by the
     it_interval member of value.  When a timer is armed with a non-zero
     it_interval, a periodic (or repetitive) timer is specified.

     Time values that are between two consecutive non-negative integer
     multiples of the resolution of the specified timer are rounded up to the
     larger multiple of the resolution.  Quantization error will not cause the
     timer to expire earlier than the rounded time value.

     If the argument ovalue is not NULL, the timer_settime() system call
     stores, in the location referenced by ovalue, a value representing the
     previous amount of time before the timer would have expired, or zero if
     the timer was disarmed, together with the previous timer reload value.
     Timers do not expire before their scheduled time.

     Only a single signal is queued to the process for a given timer at any
     point in time.  When a timer for which a signal is still pending expires,
     no signal is queued, and a timer overrun will occur.  When a timer
     expiration signal is accepted by a process, the timer_getoverrun() system
     call returns the timer expiration overrun count for the specified timer.
     The overrun count returned contains the number of extra timer expirations
     that occurred between the time the signal was generated (queued) and when
     it was accepted, up to but not including an maximum of {DELAYTIMER_MAX}.
     If the number of such extra expirations is greater than or equal to
     {DELAYTIMER_MAX}, then the overrun count is set to {DELAYTIMER_MAX}.  The
     value returned by timer_getoverrun() applies to the most recent
     expiration signal acceptance for the timer.  If no expiration signal has
     been delivered for the timer, the return value of timer_getoverrun() is
     unspecified.

RETURN VALUES

     If the timer_getoverrun() system call succeeds, it returns the timer
     expiration overrun count as explained above.  Otherwise the value -1 is
     returned, and the global variable errno is set to indicate the error.

     The timer_gettime() and timer_settime() functions return the value 0 if
     successful; otherwise the value -1 is returned and the global variable
     errno is set to indicate the error.

ERRORS

     The timer_settime() system call will fail if:

     [EINVAL]           A value structure specified a nanosecond value less
                        than zero or greater than or equal to 1000 million,
                        and the it_value member of that structure did not
                        specify zero seconds and nanoseconds.

     These system calls may fail if:

     [EINVAL]           The timerid argument does not correspond to an ID
                        returned by timer_create() but not yet deleted by
                        timer_delete().

     The timer_settime() system call may fail if:

     [EINVAL]           The it_interval member of value is not zero and the
                        timer was created with notification by creation of a
                        new thread (sigev_sigev_notify was SIGEV_THREAD) and a
                        fixed stack address has been set in the thread
                        attribute pointed to by sigev_notify_attributes.

     The timer_gettime() and timer_settime() system calls may fail if:

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

SEE ALSO

     clock_getres(2), timer_create(2), siginfo(3)

STANDARDS

     The timer_getoverrun(), timer_gettime(), and timer_settime() system calls
     conform to

HISTORY

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