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Diffstat (limited to 'share/man/man9/critical_enter.9')
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diff --git a/share/man/man9/critical_enter.9 b/share/man/man9/critical_enter.9 new file mode 100644 index 000000000000..a1d63fccd1bb --- /dev/null +++ b/share/man/man9/critical_enter.9 @@ -0,0 +1,74 @@ +.\" Copyright (c) 2001,2002 John H. Baldwin <jhb@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, 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 . |