165 lines
5.1 KiB
Groff
165 lines
5.1 KiB
Groff
.\" $NetBSD: semop.2,v 1.9 2001/09/16 01:39:02 wiz Exp $
|
|
.\"
|
|
.\" Copyright (c) 1995 Frank van der Linden
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed for the NetBSD Project
|
|
.\" by Frank van der Linden
|
|
.\" 4. The name of the author may not be used to endorse or promote products
|
|
.\" derived from this software without specific prior written permission
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
|
|
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
|
|
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
|
|
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
|
|
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
|
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
|
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
|
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
|
|
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.Dd August 25, 1999
|
|
.Dt SEMOP 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm semop
|
|
.Nd semaphore operations
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.Fd #include <sys/sem.h>
|
|
.Ft int
|
|
.Fn semop "int semid" "struct sembuf *sops" "size_t nsops"
|
|
.Sh DESCRIPTION
|
|
.Fn semop
|
|
provides a number of atomic operations on a set of semaphores. The semaphore
|
|
set is specified by
|
|
.Fa semid ,
|
|
.Fa sops
|
|
is an array of semaphore operations, and
|
|
.Fa nsops
|
|
is the number of operations in this array. The
|
|
.Va sembuf
|
|
structures in the array contain the following members:
|
|
.Bd -literal
|
|
unsigned short sem_num; /* semaphore # */
|
|
short sem_op; /* semaphore operation */
|
|
short sem_flg; /* operation flags */
|
|
.Ed
|
|
.Pp
|
|
Each operation (specified in
|
|
.Va sem_op )
|
|
is applied to semaphore number
|
|
.Va sem_num
|
|
in the set of semaphores specified by
|
|
.Fa semid .
|
|
The value of
|
|
.Va sem_op
|
|
determines the action taken in the following way:
|
|
.Bl -bullet
|
|
.It
|
|
.Va sem_op
|
|
is less than 0. The current process is blocked until the value of the
|
|
semaphore is greater than or equal to the absolute value of
|
|
.Va sem_op .
|
|
The absolute value of
|
|
.Va sem_op
|
|
is then subtracted from the value of the semaphore, and the calling
|
|
process continues. Negative values of
|
|
.Va sem_op
|
|
are thus used to enter critical regions.
|
|
.It
|
|
.Va sem_op
|
|
is greater than 0. Its value is added to the value of the specified
|
|
semaphore. This is used to leave critical regions.
|
|
.It
|
|
.Va sem_op
|
|
is equal to 0. The calling process is blocked until the value of the
|
|
specified semaphore reaches 0.
|
|
.El
|
|
.Pp
|
|
The behaviour of each operation is influenced by the flags set in
|
|
.Va sem_flg
|
|
in the following way:
|
|
.Bl -tag -width IPC_NOWAITX
|
|
.It Dv IPC_NOWAIT
|
|
In the case where the calling process would normally block, waiting
|
|
for a semaphore to reach a certain value,
|
|
.Dv IPC_NOWAIT
|
|
makes the
|
|
call return immediately, returning a value of -1 and setting
|
|
.Va errno
|
|
to
|
|
.Er EAGAIN .
|
|
.It SEM_UNDO
|
|
Keep track of the changes that this call makes to the value of a semaphore,
|
|
so that they can be undone when the calling process terminates. This is
|
|
useful to prevent other processes waiting on a semaphore to block forever,
|
|
should the process that has the semaphore locked terminate in a critical
|
|
section.
|
|
.El
|
|
.Sh RETURN VALUES
|
|
Upon successful completion, a value of 0 is returned. Otherwise, -1 is
|
|
returned and the global variable
|
|
.Va errno
|
|
is set to indicate the error.
|
|
.Sh ERRORS
|
|
.Fn semop
|
|
will fail if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
There is no semaphore associated with
|
|
.Fa semid .
|
|
.Pp
|
|
The semaphore set was removed while the process was waiting for one of
|
|
its semaphores to reach a certain value.
|
|
.It Bq Er EACCES
|
|
The calling process has no permission to access the specified semaphore set.
|
|
.It Bq Er E2BIG
|
|
The value of
|
|
.Fa nsops
|
|
is too big. The maximum is defined as
|
|
.Dv MAX_SOPS
|
|
in
|
|
.Aq Pa sys/sem.h .
|
|
.It Bq Er EFBIG
|
|
.Va sem_num
|
|
in one of the sem_buf structures is less than 0, or greater than the actual
|
|
number of semaphores in the set specified by
|
|
.Fa semid .
|
|
.It Bq Er ENOSPC
|
|
.Dv SEM_UNDO
|
|
was requested, and there is not enough space left in the kernel to
|
|
store the unfo information.
|
|
.It Bq Er EAGAIN
|
|
The requested operation can not immediately be performed, and
|
|
.Dv IPC_NOWAIT
|
|
was set in
|
|
.Va sem_flg .
|
|
.It Bq Er EFAULT
|
|
.Fa sops
|
|
points to an illegal address.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr semctl 2 ,
|
|
.Xr semget 2
|
|
.Sh STANDARDS
|
|
The
|
|
.Nm
|
|
system call conforms to
|
|
.St -xsh5 .
|
|
.Sh HISTORY
|
|
Semaphores appeared in the first release of
|
|
.At V .
|