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This function allows the caller to specify the reference clock and choose between absolute and relative mode. In relative mode, the remaining time can be returned. The API is similar to clock_nanosleep(3). Thanks to Ed Schouten for that suggestion. While I'm here, reduce the sleep time in the semaphore "child" test to greatly reduce its runtime. Also add a reasonable timeout. Reviewed by: ed (userland) MFC after: 2 weeks Relnotes: yes Sponsored by: Dell EMC Differential Revision: https://reviews.freebsd.org/D9656
162 lines
5 KiB
Groff
162 lines
5 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 February 23, 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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.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 12.0 .
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