#include <time.h> int nanosleep(const struct timespec *rqtp, struct timespec *rmtp);
The nanosleep() function causes the current thread to be suspended from execution until either the time interval specified by the rqtp argument has elapsed or a signal is delivered to the calling thread and its action is to invoke a signal-catching function or to terminate the process. The suspension time may be longer than requested because the argument value is rounded up to an integer multiple of the sleep resolution or because of the scheduling of other activity by the system. But, except for the case of being interrupted by a signal, the suspension time will not be less than the time specified by rqtp, as measured by the system clock, CLOCK_REALTIME.
The use of the nanosleep() function has no effect on the action or blockage of any signal.
If the nanosleep() function returns because the requested time has elapsed, its return value is 0.
If the nanosleep() function returns because it has been interrupted by a signal, the function returns a value of −1 and sets errno to indicate the interruption. If the rmtp argument is non-NULL, the timespec structure referenced by it is updated to contain the amount of time remaining in the interval (the requested time minus the time actually slept). If the rmtp argument is NULL, the remaining time is not returned.
If nanosleep() fails, it returns −1 and sets errno to indicate the error.
The nanosleep() function will fail if:
The nanosleep() function was interrupted by a signal.
The rqtp argument specified a nanosecond value less than zero or greater than or equal to 1000 million.
The nanosleep() function is not supported by this implementation.
See attributes(5) for descriptions of the following attributes: