.\"	$OpenBSD: refcnt_init.9,v 1.1 2015/09/11 19:13:22 dlg Exp $
.\"
.\" Copyright (c) 2015 David Gwynne <dlg@openbsd.org>
.\"
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.Dd $Mdocdate: September 11 2015 $
.Dt REFCNT_INIT 9
.Os
.Sh NAME
.Nm refcnt_init ,
.Nm refcnt_take ,
.Nm refcnt_rele ,
.Nm refcnt_rele_wake ,
.Nm refcnt_finalize ,
.Nm REFCNT_INITIALIZER
.Nd reference count API
.Sh SYNOPSIS
.In sys/refcnt.h
.Ft void
.Fn "refcnt_init" "struct refcnt *r"
.Ft void
.Fn "refcnt_take" "struct refcnt *r"
.Ft int
.Fn "refcnt_rele" "struct refcnt *r"
.Ft void
.Fn "refcnt_rele_wake" "struct refcnt *r"
.Ft void
.Fn "refcnt_finalize" "struct refcnt *r" "const char *wmesg"
.Fn "REFCNT_INITIALIZER"
.Sh DESCRIPTION
The refcnt API provides simple reference counters that can be used
to manage the lifetime of a shared object.
.Pp
.Fn refcnt_init
sets the initial value of the counter to 1 to account for the caller's
reference to the object.
.Pp
.Fn refcnt_take
is used to acquire a new reference.
It is the responsibility of the caller to guarantee that it holds
a valid reference before taking a new reference.
.Pp
.Fn refcnt_rele
is used to release an existing reference.
.Pp
.Fn refcnt_rele_wake
is used to release an existing reference and wakes up a process
that is currently waiting in
.Fn refcnt_finalize
for all the references to released.
.Pp
.Fn refcnt_finalize
releases the caller's reference and sleeps until all the other
references to the relevant object have been released.
There may only be one caller to
.Fn refcnt_finalize
per refcnt
.Fa r .
.Pp
.Fn REFCNT_INITIALIZER
initialises a declaration of a refcnt to 1.
.Sh CONTEXT
.Fn refcnt_init ,
.Fn refcnt_take ,
.Fn refcnt_rele ,
and
.Fn refcnt_rele_wake
can be called during autoconf, from process context, or from interrupt
context.
.Pp
.Fn refcnt_finalize
can be called from process context.
.Sh RETURN VALUES
.Fn refcnt_rele
returns a non-zero value if the last reference has been released,
otherwise 0.