86 lines
2.8 KiB
Groff
86 lines
2.8 KiB
Groff
|
.\"
|
||
|
.\" Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. 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(s), this list of conditions and the following disclaimer as
|
||
|
.\" the first lines of this file unmodified other than the possible
|
||
|
.\" addition of one or more copyright notices.
|
||
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
||
|
.\" notice(s), this list of conditions and the following disclaimer in the
|
||
|
.\" documentation and/or other materials provided with the distribution.
|
||
|
.\"
|
||
|
.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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.
|
||
|
.\"
|
||
|
.\" $FreeBSD$
|
||
|
.\"
|
||
|
.Dd February 26, 2001
|
||
|
.Dt SX 9
|
||
|
.Os
|
||
|
.Sh NAME
|
||
|
.Nm sx ,
|
||
|
.Nm sx_init ,
|
||
|
.Nm sx_destroy ,
|
||
|
.Nm sx_slock ,
|
||
|
.Nm sx_xlock ,
|
||
|
.Nm sx_sunlock ,
|
||
|
.Nm sx_xunlock
|
||
|
.Nd kernel shared/exclusive lock.
|
||
|
.Sh SYNOPSIS
|
||
|
.Fd #include <sys/sx.h>
|
||
|
.Ft void
|
||
|
.Fn sx_init "struct sx *sx" "const char *description"
|
||
|
.Ft void
|
||
|
.Fn sx_destroy "struct sx *sx"
|
||
|
.Ft void
|
||
|
.Fn sx_slock "struct sx *sx"
|
||
|
.Ft void
|
||
|
.Fn sx_xlock "struct sx *sx"
|
||
|
.Ft void
|
||
|
.Fn sx_sunlock "struct sx *sx"
|
||
|
.Ft void
|
||
|
.Fn sx_xunlock "struct sx *sx"
|
||
|
.Sh DESCRIPTION
|
||
|
Shared/exclusive locks are used to protect data that are read far more often
|
||
|
than they are written.
|
||
|
Mutexes are inherently more efficient than shared/exclusive locks, so
|
||
|
shared/exclusive locks should be used prudently.
|
||
|
.Pp
|
||
|
Shared/exclusive locks are created with
|
||
|
.Fn sx_init ,
|
||
|
where
|
||
|
.Fa sx
|
||
|
is a pointer to space for a
|
||
|
.Vt struct sx ,
|
||
|
and
|
||
|
.Fa description
|
||
|
is a pointer to a null-terminated character string that describes the
|
||
|
shared/exclusive lock.
|
||
|
Shared/exclusive locks are destroyed with
|
||
|
.Fn sx_destroy .
|
||
|
Threads acquire and release a shared lock by calling
|
||
|
.Fn sx_slock
|
||
|
and
|
||
|
.Fn sx_sunlock .
|
||
|
Threads acquire and release an exclusive lock by calling
|
||
|
.Fn sx_xlock
|
||
|
and
|
||
|
.Fn sx_xunlock .
|
||
|
.Pp
|
||
|
A thread may not own a shared lock and an exclusive lock simultaneously;
|
||
|
attempting to do so will result in deadlock.
|
||
|
.Sh SEE ALSO
|
||
|
.Xr mutex 9
|