.\" $OpenBSD: atomic_dec_int.9,v 1.6 2014/02/13 12:05:05 dlg Exp $
.\"
.\" Copyright (c) 2014 David Gwynne <dlg@openbsd.org>
.\" All rights reserved.
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: February 13 2014 $
.Dt ATOMIC_DEC_INT 9
.Os
.Sh NAME
.Nm atomic_dec_int ,
.Nm atomic_dec_int_nv ,
.Nm atomic_dec_long ,
.Nm atomic_dec_long_nv
.Nd atomic decrement operations
.Sh SYNOPSIS
.In sys/atomic.h
.Ft void
.Fn atomic_dec_int "volatile unsigned int *p"
.Ft unsigned int
.Fn atomic_dec_int_nv "volatile unsigned int *p"
.Ft void
.Fn atomic_dec_long "volatile unsigned long *p "
.Ft unsigned long
.Fn atomic_dec_long_nv "volatile unsigned long *p"
.Sh DESCRIPTION
The atomic_dec set of functions provide an interface for atomically
performing decrement and decrement-and-fetch operations with respect
to interrupts and multiple processors in the system.
.Pp
The value referenced by the pointer
.Fa p
is decremented by 1.
.Sh CONTEXT
.Fn atomic_dec_int ,
.Fn atomic_dec_int_nv ,
.Fn atomic_dec_long ,
and
.Fn atomic_dec_long_nv
can all be called during autoconf, from process context, or from interrupt context.
.Sh RETURN VALUES
.Nm atomic_dec_int
and
.Nm atomic_dec_long
perform the decrement without returning any knowledge of the value at
.Fa p .
.Pp
.Nm atomic_dec_int_nv
and
.Nm atomic_dec_long_nv
return the value at
.Fa p
after the decrement was performed.
.Sh SEE ALSO
.Xr atomic_add_int 9 ,
.Xr atomic_inc_int 9
.Sh HISTORY
The atomic_add functions first appeared in
.Nx 5.0
and
.Ox 5.5 .