164 lines
5.0 KiB
Groff
164 lines
5.0 KiB
Groff
.\" Copyright (c) 2008, David Xu <davidxu@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" Portions of this text are reprinted and reproduced in electronic form
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.\" from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --
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.\" Portable Operating System Interface (POSIX), The Open Group Base
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.\" Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of
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.\" Electrical and Electronics Engineers, Inc and The Open Group. In the
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.\" event of any discrepancy between this version and the original IEEE and
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.\" The Open Group Standard, the original IEEE and The Open Group Standard is
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.\" the referee document. The original Standard can be obtained online at
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.\" http://www.opengroup.org/unix/online.html.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 24, 2017
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.Dt SEM_TIMEDWAIT 3
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.Os
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.Sh NAME
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.Nm sem_timedwait ,
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.Nm sem_clockwait_np
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.Nd "lock a semaphore"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In semaphore.h
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.In time.h
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.Ft int
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.Fn sem_timedwait "sem_t * restrict sem" "const struct timespec * restrict abs_timeout"
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.Ft int
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.Fn sem_clockwait_np "sem_t * restrict sem" "clockid_t clock_id" "int flags" "const struct timespec * rqtp" "struct timespec * rmtp"
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.Sh DESCRIPTION
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The
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.Fn sem_timedwait
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function locks the semaphore referenced by
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.Fa sem ,
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as in the
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.Xr sem_wait 3
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function.
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However, if the semaphore cannot be locked without waiting for
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another process or thread to unlock the semaphore by performing
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a
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.Xr sem_post 3
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function, this wait will be terminated when the specified timeout expires.
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.Pp
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The timeout will expire when the absolute time specified by
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.Fa abs_timeout
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passes, as measured by the clock on which timeouts are based (that is,
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when the value of that clock equals or exceeds
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.Fa abs_timeout ) ,
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or if the
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absolute time specified by
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.Fa abs_timeout
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has already been passed at the time of the call.
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.Pp
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Note that the timeout is based on the
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.Dv CLOCK_REALTIME
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clock.
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.Pp
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The validity of the
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.Fa abs_timeout
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is not checked if the semaphore can be locked immediately.
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.Pp
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The
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.Fn sem_clockwait_np
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function is a more flexible variant of
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.Fn sem_timedwait .
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The
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.Fa clock_id
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parameter specifies the reference clock.
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If the
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.Fa flags
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parameter contains
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.Dv TIMER_ABSTIME ,
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then the requested timeout
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.Pq Fa rqtp
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is an absolute timeout; otherwise,
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the timeout is relative.
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If this function fails with
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.Er EINTR
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and the timeout is relative,
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a non-NULL
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.Fa rmtp
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will be updated to contain the amount of time remaining in the interval
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.Po
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the requested time minus the time actually slept
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.Pc .
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An absolute timeout has no effect on
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.Fa rmtp .
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A single structure can be used for both
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.Fa rqtp
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and
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.Fa rmtp .
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.Sh RETURN VALUES
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These
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functions return zero if the calling process successfully performed the
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semaphore lock operation on the semaphore designated by
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.Fa sem .
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If the call was unsuccessful, the state of the semaphore is unchanged,
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and the function returns a value of \-1 and sets the global variable
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.Va errno
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to indicate the error.
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.Sh ERRORS
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These functions will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa sem
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argument does not refer to a valid semaphore, or the process or thread would
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have blocked, and the
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.Fa abs_timeout
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parameter specified a nanoseconds field value less than zero or greater than
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or equal to 1000 million.
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.It Bq Er ETIMEDOUT
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The semaphore could not be locked before the specified timeout expired.
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.It Bq Er EINTR
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A signal interrupted this function.
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.El
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.Sh SEE ALSO
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.Xr sem_post 3 ,
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.Xr sem_trywait 3 ,
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.Xr sem_wait 3
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.Sh STANDARDS
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The
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.Fn sem_timedwait
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function conforms to
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.St -p1003.1-2004 .
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The
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.Fn sem_clockwait_np
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function is not specified by any standard;
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it exists only on
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.Fx
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at the time of this writing.
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.Sh HISTORY
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The
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.Fn sem_timedwait
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function first appeared in
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.Fx 5.0 .
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The
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.Fn sem_clockwait_np
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function first appeared in
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.Fx 11.1 .
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