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#include <time.h>
int timer_settime(timer_t timerid, int flags, const struct itimerspec *value, struct itimerspec *ovalue);
int timer_gettime(timer_t timerid, struct itimerspec *value);
int timer_getoverrun(timer_t timerid);
struct
itimerspec {
struct timespec it_interval; /* timer period */
struct timespec it_value; /* timer expiration */
};
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* and nanoseconds */
};
value->it_value may be expressed as either an absolute or relative time. If flags is set to TIMER_RELTIME, then the timer will initially expire relative to when the call is made. If flags is set to TIMER_ABSTIME, then the initial expiration will be relative to 00:00 Universal Coordinated Time, January 1, 1970. If the specified (absolute) time has already passed, timer_settime() succeeds and the expiration notification is made.
If value->it_interval is non-zero, then timerid, will be a ‘"periodic’ timer, to be reloaded to expire every value->it_interval seconds (nanoseconds). Otherwise, if value->it_interval is zero and value->it_value is non-zero, then timerid is a ‘one-shot’ timer, which will expire only at the time specified by value->it_value.
If ovalue is not NULL, and timer timerid had previously been used, then timer_settime() will store the remaining time until the previous timer expires in ovalue->it_value, and the previous reload interval in ovalue->it_interval. (If the previous timer was disarmed, ovalue->it_value will be set to zero). The values stored in ovalue by timer_settime() are the same values that would have been returned by a call to timer_gettime( timerid,...).
timer_gettime() stores the amount of time until the specified timer, timerid, expires into value->it_value, and the timer’s reload value into value->it_interval.
Only a single signal can be queued to the LWP for a given timer at any point in time. When a timer, for which a signal is still pending expires, (from a previous interval), no signal will be queued, and a ‘timer overrun count’ will be incremented. When a timer expiration signal is delivered to an LWP, timer_overrun() may be used to determine the timer expiration overrun count for the specified timer. The overrun count returned contains the number of extra timer expirations which occurred between the time the signal was generated (queued) and when it was delivered, up to but not including a 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 delivery for the timer.