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Fully catch up to the recent critical section API change. Update the

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content of the manpage and document cpu_critical_enter/exit.
This commit is contained in:
jhb 2002-01-04 23:56:17 +00:00
parent 3e1c28c2da
commit f565bf39a4
2 changed files with 43 additions and 11 deletions
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2
share/man/man9/Makefile
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@ -120,6 +120,8 @@ MLINKS+=condvar.9 cv_waitq_empty.9
MLINKS+=condvar.9 cv_wmesg.9
MLINKS+=copy.9 copyin.9 copy.9 copyinstr.9 copy.9 copyout.9 copy.9 copystr.9
MLINKS+=critical_enter.9 critical_exit.9
MLINKS+=critical_enter.9 cpu_critical_enter.9
MLINKS+=critical_enter.9 cpu_critical_exit.9
MLINKS+=device_ids.9 major.9 device_ids.9 minor.9
MLINKS+=device_ids.9 umajor.9 device_ids.9 uminor.9
MLINKS+=devstat.9 devicestat.9 devstat.9 devstat_add_entry.9

52
share/man/man9/critical_enter.9
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@ -1,4 +1,4 @@
.\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org>
.\" Copyright (c) 2001,2002 John H. Baldwin <jhb@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
@ -28,30 +28,57 @@
.Dt CRITICAL_ENTER 9
.Os
.Sh NAME
.Nm cpu_critical_enter ,
.Nm cpu_critical_exit ,
.Nm critical_enter ,
.Nm critical_exit
.Nd enter and exit a critical region
.Sh SYNOPSIS
.In sys/types.h
.In sys/systm.h
.Ft critical_t
.Fn cpu_critical_enter "void"
.Ft void
.Fn cpu_critical_exit "critical_t savecrit"
.Ft void
.Fn critical_enter "void"
.Ft void
.Fn critical_exit "void"
.Sh DESCRIPTION
These functions are used to prevent preemption in a critcal region of code.
All that is guaranteed is that the current CPU will not be preempted by an
external interrupt.
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.
section; however, these faults are usually fatal.
.Pp
The
.Fn critical_enter
.Fn cpu_critical_enter
and
.Fn cpu_critical_exit
functions provide the machine dependent disabling of preemption, normally
by disabling interrupts on the local CPU.
The
.Fn cpu_critical_enter
function returns an opaque value of type
.Vt critical_t .
This value must be passed to the
.Fn critical_exit
.Fn cpu_critical_exit
function when leaving the critical region.
.Pp
The
.Fn critical_enter
and
.Fn critical_exit
functions provide a machine independent wrapper around the machine dependent
API.
This wrapper currently saves state regarding nested critical sections as
well as the
.Vt critical_t
value inside of a critical region in per-thread variables.
Nearly all code should use these versions of the API.
.Pp
Note that these functions are not required to provide any inter-CPU
synchronization, data protection, or memory ordering guarantees and thus
should
@ -60,11 +87,15 @@ 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, the machine dependent and machine independent functions should not
be interlocked, and neither pair of functions should be interlocked with
operations on mutexes, sx locks, semaphores, or other synchronization
primitives.
.Sh RETURN VALUES
The
.Fn critical_enter
.Fn cpu_critical_enter
function returns an opaque value that must be passed to a corresponding call to
.Fn critical_exit .
.Fn cpu_critical_exit .
.Sh EXAMPLES
This example demonstrates the use of
.Fn critical_enter
@ -78,17 +109,16 @@ isa_dmastatus(int chan)
u_long cnt = 0;
int ffport, waport;
u_long low1, high1, low2, high2;
critical_t savecrit;
...
savecrit = critical_enter();
critical_enter();
outb(ffport, 0);
low1 = inb(waport);
high1 = inb(waport);
outb(ffport, 0);
low2 = inb(waport);
high2 = inb(waport);
critical_exit(savecrit);
critical_exit();
...
}
.Ed