208 lines
4.9 KiB
Groff
208 lines
4.9 KiB
Groff
.\" $NetBSD: hashinit.9,v 1.3 2006/12/23 06:36:19 wiz Exp $
|
|
.\"
|
|
.\" Copyright (c) 2006 The NetBSD Foundation, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to The NetBSD Foundation
|
|
.\" by Chapman Flack.
|
|
.\"
|
|
.\" 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.
|
|
.\" 3. Neither the name of The NetBSD Foundation nor the names of its
|
|
.\" contributors may be used to endorse or promote products derived
|
|
.\" from this software without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
|
|
.\"
|
|
.Dd June 3, 2006
|
|
.Dt HASHINIT 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm hashinit ,
|
|
.Nm hashdone
|
|
.Nd kernel hash table construction and destruction
|
|
.Sh SYNOPSIS
|
|
.In sys/malloc.h
|
|
.In sys/systm.h
|
|
.Ft "void *"
|
|
.Fo hashinit
|
|
.Fa "u_int chains"
|
|
.Fa "enum hashtype htype"
|
|
.Fa "struct malloc_type *mtype"
|
|
.Fa "int mflags"
|
|
.Fa "u_long *hashmask"
|
|
.Fc
|
|
.Ft void
|
|
.Fn hashdone "void *hashtbl" "struct malloc_type *mtype"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn hashinit
|
|
function allocates and initializes space for a simple chaining hash table.
|
|
The number of slots will be the least power of two not smaller than
|
|
.Fa chains .
|
|
The customary choice for
|
|
.Fa chains
|
|
is the maximum number of elements you intend to store divided by
|
|
your intended load factor.
|
|
The
|
|
.Dv LIST...
|
|
or
|
|
.Dv TAILQ...
|
|
macros of
|
|
.Xr queue 3
|
|
can be used to manipulate the chains; pass
|
|
.Dv HASH_LIST
|
|
or
|
|
.Dv HASH_TAILQ
|
|
as
|
|
.Fa htype
|
|
to indicate which. Each slot will be initialized as the head of an empty
|
|
chain of the proper type. Because different data structures from
|
|
.Xr queue 3
|
|
can define head structures of different sizes, the total size of the
|
|
allocated table can vary with the choice of
|
|
.Fa htype .
|
|
.Pp
|
|
The
|
|
.Fa mtype
|
|
and
|
|
.Fa mflags
|
|
arguments have the meanings of the corresponding arguments to
|
|
.Xr malloc 9 .
|
|
.Pp
|
|
A value will be stored into
|
|
.Fa *hashmask
|
|
suitable for masking any computed hash, to obtain the index of a chain
|
|
head in the allocated table.
|
|
.Pp
|
|
The
|
|
.Fn hashdone
|
|
function deallocates the storage allocated by
|
|
.Fn hashinit
|
|
and pointed to by
|
|
.Fa hashtbl ,
|
|
given the same
|
|
.Fa mtype
|
|
that was passed to
|
|
.Fn hashinit .
|
|
If the table contains any nonempty chain when
|
|
.Fn hashdone
|
|
is called, the result is undefined.
|
|
.Sh RETURN VALUES
|
|
The value returned by
|
|
.Fn hashinit
|
|
should be cast as pointer to an array of
|
|
.Dv LIST_HEAD
|
|
or
|
|
.Dv TAILQ_HEAD
|
|
as appropriate.
|
|
It can be
|
|
.Dv NULL
|
|
only if the specified
|
|
.Fa mflags
|
|
allow it.
|
|
.Sh SEE ALSO
|
|
.Xr queue 3 ,
|
|
.Xr hash 9 ,
|
|
.Xr malloc 9
|
|
.Sh CODE REFERENCES
|
|
These functions are implemented in
|
|
.Pa sys/kern/kern_subr.c .
|
|
.Sh HISTORY
|
|
A
|
|
.Fn hashinit
|
|
function was present, without the
|
|
.Fa htype
|
|
or
|
|
.Fa mflags
|
|
arguments, in
|
|
.Bx 4.4 alpha .
|
|
It was independent of
|
|
.Xr queue 3
|
|
and simply allocated and nulled a table of pointer-sized slots.
|
|
It sized the table to the
|
|
.Em largest
|
|
power of two
|
|
.Em not greater than
|
|
.Fa chains ;
|
|
that is, it built in a load factor between 1 and 2.
|
|
.Pp
|
|
.Nx 1.0
|
|
was the first
|
|
.Nx
|
|
release to have a
|
|
.Fn hashinit
|
|
function.
|
|
It resembled that from
|
|
.Bx 4.4
|
|
but made each slot a
|
|
.Dv LIST_HEAD
|
|
from
|
|
.Xr queue 3 .
|
|
For
|
|
.Nx 1.3.3
|
|
it had been changed to size the table to the least power of two
|
|
not less than
|
|
.Em or equal to
|
|
.Fa chains .
|
|
By
|
|
.Nx 1.4
|
|
it had the
|
|
.Fa mflags
|
|
argument and the current sizing rule.
|
|
.Pp
|
|
.Nx 1.5
|
|
had the
|
|
.Fn hashdone
|
|
function.
|
|
By
|
|
.Nx 1.6
|
|
.Fn hashinit
|
|
supported
|
|
.Dv LIST
|
|
or
|
|
.Dv TAILQ
|
|
chains selected with
|
|
.Fa htype .
|
|
.Pp
|
|
.Fx
|
|
has a
|
|
.Fn hashinit
|
|
with behavior equivalent (as of
|
|
.Fx 6.1 )
|
|
to that in
|
|
.Nx 1.0 ,
|
|
and a
|
|
.Fn hashdestroy
|
|
that behaves as
|
|
.Fn hashdone
|
|
but checks that all chains are empty first.
|
|
.Ox
|
|
has a
|
|
.Fn hashinit
|
|
comparable (as of
|
|
.Ox 3.9 )
|
|
to that of
|
|
.Nx 1.4 .
|
|
This manual page was added for
|
|
.Nx 4.0 .
|
|
.Sh BUGS
|
|
The only part of the work of implementing a hash table that these functions
|
|
relieve is the part that isn't much work.
|