The timer_settime() function sets the time until the next expiration of the timer specified by timerid from the it_value member of the value argument and arm 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 0, the timer is disarmed. The effect of disarming or resetting a timer on pending expiration notifications is unspecified.
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 function 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 will be 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 function timer_settime() stores, in the location referenced by ovalue, a value representing the previous amount of time before the timer would have expired
or 0 if the timer was disarmed, together with the previous timer reload value. The members of ovalue are subject to the resolution of the timer, and they are the same values that would be returned by a timer_gettime() call at that point in time.
The timer_gettime() function 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 0 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().
Only a single signal will be 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 will be queued, and a timer overrun occurs. When a timer expiration signal is delivered to or accepted by a process, the timer_getoverrun() function 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 delivered or accepted, up to but not including an implementation-dependent
maximum of DELAYTIMER_MAX. If the number of such extra expirations is greater than or equal to DELAYTIMER_MAX, then the overrun count will be set to DELAYTIMER_MAX. The value returned by timer_getoverrun() applies to the most
recent expiration signal delivery or acceptance for the timer. If no expiration signal has been delivered for the timer, the meaning of the overrun count returned is undefined.