2e43efd0bb
Reviewed by: rgrimes MFC after: 1 month Differential Revision: https://reviews.freebsd.org/D19485
74 lines
3.0 KiB
Groff
74 lines
3.0 KiB
Groff
.\" Copyright (c) 2001,2002 John H. Baldwin <jhb@FreeBSD.org>
|
|
.\"
|
|
.\" 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.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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 October 5, 2005
|
|
.Dt CRITICAL_ENTER 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm critical_enter ,
|
|
.Nm critical_exit
|
|
.Nd enter and exit a critical region
|
|
.Sh SYNOPSIS
|
|
.In sys/param.h
|
|
.In sys/systm.h
|
|
.Ft void
|
|
.Fn critical_enter "void"
|
|
.Ft void
|
|
.Fn critical_exit "void"
|
|
.Sh DESCRIPTION
|
|
These functions are used to prevent preemption in a critical region of code.
|
|
All that is guaranteed is that the thread currently executing on a CPU will
|
|
not be preempted.
|
|
Specifically, a thread in a critical region will not migrate to another
|
|
CPU while it is in a critical region.
|
|
The current CPU may still trigger faults and exceptions during a critical
|
|
section; however, these faults are usually fatal.
|
|
.Pp
|
|
The
|
|
.Fn critical_enter
|
|
and
|
|
.Fn critical_exit
|
|
functions manage a per-thread counter to handle nested critical sections.
|
|
If a thread is made runnable that would normally preempt the current thread
|
|
while the current thread is in a critical section,
|
|
then the preemption will be deferred until the current thread exits the
|
|
outermost critical section.
|
|
.Pp
|
|
Note that these functions are not required to provide any inter-CPU
|
|
synchronization, data protection, or memory ordering guarantees and thus
|
|
should
|
|
.Em not
|
|
be used to protect shared data structures.
|
|
.Pp
|
|
These functions should be used with care as an infinite loop within a
|
|
critical region will deadlock the CPU.
|
|
Also, they should not be interlocked with operations on mutexes, sx locks,
|
|
semaphores, or other synchronization primitives.
|
|
One exception to this is that spin mutexes include a critical section,
|
|
so in certain cases critical sections may be interlocked with spin mutexes.
|
|
.Sh HISTORY
|
|
These functions were introduced in
|
|
.Fx 5.0 .
|