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Add a simple manage for the refcount(9) API.

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Requested by:	rwatson
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jhb 2009-03-30 18:01:12 +00:00
parent 5bf93e3bc7
commit f821c33568
2 changed files with 100 additions and 0 deletions
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4
share/man/man9/Makefile
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@ -201,6 +201,7 @@ MAN= accept_filter.9 \
random.9 \
random_harvest.9 \
redzone.9 \
refcount.9 \
resettodr.9 \
resource_int_value.9 \
rijndael.9 \
@ -920,6 +921,9 @@ MLINKS+=random.9 arc4rand.9 \
random.9 arc4random.9 \
random.9 read_random.9 \
random.9 srandom.9
MLINKS+=refcount.9 refcount_acquire.9 \
refcount.9 refcount_init.9 \
refcount.9 refcount_release.9
MLINKS+=resource_int_value.9 resource_long_value.9 \
resource_int_value.9 resource_string_value.9
MLINKS+=rman.9 rman_activate_resource.9 \

96
share/man/man9/refcount.9 Normal file
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@ -0,0 +1,96 @@
.\"
.\" Copyright (c) 2009 Advanced Computing Technologies LLC
.\" Written by: 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 January 20, 2009
.Dt REFCOUNT 9
.Os
.Sh NAME
.Nm refcount ,
.Nm refcount_init ,
.Nm refcount_acquire ,
.Nm refcount_release
.Nd manage a simple reference counter
.Sh SYNOPSIS
.In sys/param.h
.In sys/refcount.h
.Ft void
.Fn refcount_init "volatile u_int *count, u_int value"
.Ft void
.Fn refcount_acquire "volatile u_int *count"
.Ft int
.Fn refcount_release "volatile u_int *count"
.Sh DESCRIPTION
The
.Nm
functions provide an API to manage a simple reference counter.
The caller provides the storage for the counter in an unsigned integer.
A pointer to this integer is passed via
.Fa count .
Usually the counter is used to manage the lifetime of an object and is
stored as a member of the object.
.Pp
The
.Fn refcount_init
function is used to set the initial value of the counter to
.Fa value .
It is normally used when creating a reference-counted object.
.Pp
The
.Fn refcount_acquire
function is used to acquire a new reference.
The caller is responsible for ensuring that it holds a valid reference
while obtaining a new reference.
For example,
if an object is stored on a list and the list holds a reference on the
object, then holding a lock that protects the list provides sufficient
protection for acquiring a new reference.
.Pp
The
.Fn refcount_release
function is used to release an existing reference.
The function returns a non-zero value if the reference being released was
the last reference;
otherwise, it returns zero.
.Pp
Note that these routines do not provide any inter-CPU synchronization,
data protection,
or memory ordering guarantees except for managing the counter.
The caller is responsible for any additional synchronization needed by
consumers of any containing objects.
In addition,
the caller is also responsible for managing the life cycle of any containing
objects including explicitly releasing any resources when the last reference
is released.
.Sh RETURN VALUES
The
.Nm refcount_release
function returns non-zero when releasing the last reference and zero when
releasing any other reference.
.Sh HISTORY
These functions were introduced in
.Fx 6.0 .