#include <unistd.h>unsigned int sleep(unsigned int seconds);
The current process is suspended from execution for the number of seconds specified by the argument. The actual suspension time may be less than that requested because any caught signal will terminate the sleep() following execution of that signal's catching routine. Also, the suspension time may be longer than requested by an arbitrary amount because of the scheduling of other activity in the system. The value returned by sleep() will be the ``unslept'' amount (the requested time minus the time actually slept) in case the caller had an alarm set to go off earlier than the end of the requested sleep() time, or premature arousal because of another caught signal.
In a single-threaded program (one not linked with -lthread or -lpthread), the routine is implemented by setting an alarm signal and pausing until it (or some other signal) occurs. The previous state of the alarm signal is saved and restored. The calling program may have set up an alarm signal before calling sleep(). If the sleep() time exceeds the time until such alarm signal, the process sleeps only until the alarm signal would have occurred. The caller's alarm catch routine is executed just before the sleep() routine returns. But if the sleep() time is less than the time till such alarm, the prior alarm time is reset to go off at the same time it would have without the intervening sleep().
In a multithreaded program (one linked with -lthread or -lpthread), the routine is implemented with a call to the nanosleep(3RT) function and does not modify the state of the alarm signal.
See attributes(5) for descriptions of the following attributes:
|ATTRIBUTE TYPE||ATTRIBUTE VALUE|
In a single-threaded program, the
SIGALRM signal should not be blocked or ignored during a call to sleep(). This restriction does not apply to a multithreaded program.
In a multithreaded program, only the invoking thread is suspended from execution.