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Name

sleep - suspend execution for interval

Synopsis

#include <unistd.h>

unsigned sleep(unsigned seconds);

MT-Level

Safe

Description

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.

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().

See Also

alarm(2) , pause(2) , signal(3C)

Notes

SIGALRM should not be blocked or ignored during a call to sleep(). Only a prior call to alarm(2) should generate SIGALRM for the calling process during a call to sleep().

In a multithreaded program, only the invoking thread is suspended from execution.

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