sleep -- suspend execution for interval


cc . . . -lc

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 for two reasons: (1) Because scheduled wakeups occur at fixed 1-second intervals, (on the second, according to an internal clock) and (2) because any caught signal terminates the sleep following execution of that signal's catching routine. Also, the suspension time may be longer than requested by an arbitrary amount due to the scheduling of other activity in the system. The value returned by sleep is 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 due to 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 till 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(S), pause(S), sigaction(S)

Standards conformance

sleep is conformant with:

X/Open Portability Guide, Issue 3, 1989 ;
IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C Language] (ISO/IEC 9945-1) ;
and NIST FIPS 151-1 .

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SCO OpenServer Release 5.0.7 -- 11 February 2003