sleep(3ucb) [opensolaris man page]
sleep(3UCB) SunOS/BSD Compatibility Library Functions sleep(3UCB)
NAME
sleep - suspend execution for interval
SYNOPSIS
/usr/ucb/cc [ flag ... ] file ...
int sleep(seconds)
unsigned seconds;
DESCRIPTION
sleep() suspends the current process from execution for the number of seconds specified by the argument. The actual suspension time may be
up to 1 second less than that requested, because scheduled wakeups occur at fixed 1-second intervals, and may be an arbitrary amount longer
because of other activity in the system.
sleep() is implemented by setting an interval timer and pausing until it expires. The previous state of this timer is saved and restored.
If the sleep time exceeds the time to the expiration of the previous value of the timer, the process sleeps only until the timer would have
expired, and the signal which occurs with the expiration of the timer is sent one second later.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|MT-Level |Async-Signal-Safe |
+-----------------------------+-----------------------------+
SEE ALSO
cc(1B), alarm(2), getitimer(2), longjmp(3C), siglongjmp(3C), sleep(3C), usleep(3C), attributes(5)
NOTES
Use of these interfaces should be restricted to only applications written on BSD platforms. Use of these interfaces with any of the system
libraries or in multi-thread applications is unsupported.
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(). A signal-catching function should not interrupt a call to sleep() to call siglongjmp(3C) or longjmp(3C)
to restore an environment saved prior to the sleep() call.
WARNINGS
sleep() is slightly incompatible with alarm(2). Programs that do not execute for at least one second of clock time between successive calls
to sleep() indefinitely delay the alarm signal. Use sleep(3C). Each sleep(3C) call postpones the alarm signal that would have been sent
during the requested sleep period to occur one second later.
SunOS 5.11 30 Oct 2007 sleep(3UCB)
Check Out this Related Man Page
SLEEP(3P) POSIX Programmer's Manual SLEEP(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
sleep - suspend execution for an interval of time
SYNOPSIS
#include <unistd.h>
unsigned sleep(unsigned seconds);
DESCRIPTION
The sleep() function shall cause the calling thread to be suspended from execution until either the number of realtime seconds specified by
the argument seconds 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 due to the scheduling of other activity by the system.
If a SIGALRM signal is generated for the calling process during execution of sleep() and if the SIGALRM signal is being ignored or blocked
from delivery, it is unspecified whether sleep() returns when the SIGALRM signal is scheduled. If the signal is being blocked, it is also
unspecified whether it remains pending after sleep() returns or it is discarded.
If a SIGALRM signal is generated for the calling process during execution of sleep(), except as a result of a prior call to alarm(), and if
the SIGALRM signal is not being ignored or blocked from delivery, it is unspecified whether that signal has any effect other than causing
sleep() to return.
If a signal-catching function interrupts sleep() and examines or changes either the time a SIGALRM is scheduled to be generated, the action
associated with the SIGALRM signal, or whether the SIGALRM signal is blocked from delivery, the results are unspecified.
If a signal-catching function interrupts sleep() and calls siglongjmp() or longjmp() to restore an environment saved prior to the sleep()
call, the action associated with the SIGALRM signal and the time at which a SIGALRM signal is scheduled to be generated are unspecified. It
is also unspecified whether the SIGALRM signal is blocked, unless the process' signal mask is restored as part of the environment.
Interactions between sleep() and any of setitimer(), ualarm(), or usleep() are unspecified.
RETURN VALUE
If sleep() returns because the requested time has elapsed, the value returned shall be 0. If sleep() returns due to delivery of a signal,
the return value shall be the "unslept" amount (the requested time minus the time actually slept) in seconds.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
There are two general approaches to the implementation of the sleep() function. One is to use the alarm() function to schedule a SIGALRM
signal and then suspend the process waiting for that signal. The other is to implement an independent facility. This volume of
IEEE Std 1003.1-2001 permits either approach.
In order to comply with the requirement that no primitive shall change a process attribute unless explicitly described by this volume of
IEEE Std 1003.1-2001, an implementation using SIGALRM must carefully take into account any SIGALRM signal scheduled by previous alarm()
calls, the action previously established for SIGALRM, and whether SIGALRM was blocked. If a SIGALRM has been scheduled before the sleep()
would ordinarily complete, the sleep() must be shortened to that time and a SIGALRM generated (possibly simulated by direct invocation of
the signal-catching function) before sleep() returns. If a SIGALRM has been scheduled after the sleep() would ordinarily complete, it must
be rescheduled for the same time before sleep() returns. The action and blocking for SIGALRM must be saved and restored.
Historical implementations often implement the SIGALRM-based version using alarm() and pause(). One such implementation is prone to infi-
nite hangups, as described in pause(). Another such implementation uses the C-language setjmp() and longjmp() functions to avoid that win-
dow. That implementation introduces a different problem: when the SIGALRM signal interrupts a signal-catching function installed by the
user to catch a different signal, the longjmp() aborts that signal-catching function. An implementation based on sigprocmask(), alarm(),
and sigsuspend() can avoid these problems.
Despite all reasonable care, there are several very subtle, but detectable and unavoidable, differences between the two types of implemen-
tations. These are the cases mentioned in this volume of IEEE Std 1003.1-2001 where some other activity relating to SIGALRM takes place,
and the results are stated to be unspecified. All of these cases are sufficiently unusual as not to be of concern to most applications.
See also the discussion of the term realtime in alarm() .
Since sleep() can be implemented using alarm(), the discussion about alarms occurring early under alarm() applies to sleep() as well.
Application writers should note that the type of the argument seconds and the return value of sleep() is unsigned. That means that a
Strictly Conforming POSIX System Interfaces Application cannot pass a value greater than the minimum guaranteed value for {UINT_MAX}, which
the ISO C standard sets as 65535, and any application passing a larger value is restricting its portability. A different type was consid-
ered, but historical implementations, including those with a 16-bit int type, consistently use either unsigned or int.
Scheduling delays may cause the process to return from the sleep() function significantly after the requested time. In such cases, the
return value should be set to zero, since the formula (requested time minus the time actually spent) yields a negative number and sleep()
returns an unsigned.
FUTURE DIRECTIONS
None.
SEE ALSO
alarm(), getitimer(), nanosleep(), pause(), sigaction(), sigsetjmp(), ualarm(), usleep(), the Base Definitions volume of
IEEE Std 1003.1-2001, <unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
online at http://www.opengroup.org/unix/online.html .
IEEE
/The Open Group 2003 SLEEP(3P)