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diff --git a/share/man/man9/refcount.9 b/share/man/man9/refcount.9 new file mode 100644 index 000000000000..e7702a22661e --- /dev/null +++ b/share/man/man9/refcount.9 @@ -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 . |