#include <unistd.h> int usleep(useconds_t useconds);
The usleep() function suspends the caller from execution for the number of microseconds specified by the useconds argument. The actual suspension time might be less than requested because any caught signal will terminate usleep() following execution of that signal's catching routine. The suspension time might be longer than requested by an arbitrary amount because of the scheduling of other activity in the system.
If the value of useconds is 0, then the call has no effect.
The use of the usleep() function has no effect on the action or blockage of any signal. In a multithreaded process, only the invoking thread is suspended from execution.
On completion, usleep() returns 0. There are no error returns.
No errors are returned.
The usleep() function is included for its historical usage. The nanosleep(3C) function is preferred over this function.
See attributes(5) for descriptions of the following attributes: