cdebd14937
libopenbsd is an internal library which to bring in compatibility stuff from OpenBSD. This will allow us to bring in more OpenBSD utilities into the FreeBSD base system. We similarly use libnetbsd for bringing in stuff from NetBSD. Reviewed by: bapt Differential Revision: https://reviews.freebsd.org/D4078
274 lines
6.7 KiB
Groff
274 lines
6.7 KiB
Groff
.\" $OpenBSD: ohash_init.3,v 1.2 2014/05/13 14:01:41 jmc Exp $
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.\" Copyright (c) 1999 Marc Espie <espie@openbsd.org>
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 12, 2014
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.Dt OHASH_INIT 3
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.Os
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.Sh NAME
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.Nm ohash_init ,
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.Nm ohash_delete ,
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.Nm ohash_lookup_interval ,
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.Nm ohash_lookup_memory ,
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.Nm ohash_find ,
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.Nm ohash_remove ,
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.Nm ohash_insert ,
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.Nm ohash_first ,
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.Nm ohash_next ,
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.Nm ohash_entries
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.Nd light-weight open hashing
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.Sh SYNOPSIS
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.In stdint.h
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.In stddef.h
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.In ohash.h
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.Ft void
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.Fn ohash_init "struct ohash *h" "unsigned int size" "struct ohash_info *info"
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.Ft void
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.Fn ohash_delete "struct ohash *h"
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.Ft "unsigned int"
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.Fn ohash_lookup_interval "struct ohash *h" "const char *start" "const char *end" "uint32_t hv"
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.Ft "unsigned int"
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.Fn ohash_lookup_memory "struct ohash *h" "const char *k" "size_t s" "uint32_t hv"
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.Ft void *
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.Fn ohash_find "struct ohash *h" "unsigned int i"
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.Ft void *
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.Fn ohash_remove "struct ohash *h" "unsigned int i"
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.Ft void *
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.Fn ohash_insert "struct ohash *h" "unsigned int i" "void *p"
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.Ft void *
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.Fn ohash_first "struct ohash *h" "unsigned int *i"
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.Ft void *
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.Fn ohash_next "struct ohash *h" "unsigned int *i"
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.Ft "unsigned int"
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.Fn ohash_entries "struct ohash *h"
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.Sh DESCRIPTION
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These functions have been designed as a fast, extensible alternative to
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the usual hash table functions.
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They provide storage and retrieval of records indexed by keys,
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where a key is a contiguous sequence of bytes at a fixed position in
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each record.
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Keys can either be NUL-terminated strings or fixed-size memory areas.
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All functions take a pointer to an ohash structure as the
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.Fa h
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function argument.
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Storage for this structure should be provided by user code.
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.Pp
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.Fn ohash_init
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initializes the table to store roughly 2 to the power
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.Fa size
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elements.
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.Fa info
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is a pointer to a
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.Fa struct ohash_info .
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.Bd -literal -offset indent
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struct ohash_info {
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ptrdiff_t key_offset;
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void *data; /* user data */
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void *(*calloc)(size_t, size_t, void *);
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void (*free)(void *, void *);
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void *(*alloc)(size_t, void *);
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};
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.Ed
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.Pp
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The
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.Va offset
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field holds the position of the key in each record;
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the
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.Va calloc
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and
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.Va free
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fields are pointers to
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.Xr calloc 3
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and
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.Xr free 3 Ns -like
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functions, used for managing the table internal storage;
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the
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.Va alloc
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field is only used by the utility function
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.Xr ohash_create_entry 3 .
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.Pp
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Each of these functions are called similarly to their standard counterpart,
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but with an extra
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.Ft void *
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parameter corresponding to the content of the field
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.Fa data ,
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which can be used to communicate specific information to the functions.
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.Pp
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.Fn ohash_init
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stores a copy of those fields internally, so
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.Fa info
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can be reclaimed after initialization.
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.Pp
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.Fn ohash_delete
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frees storage internal to
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.Fa h .
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Elements themselves should be freed by the user first, using for instance
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.Fn ohash_first
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and
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.Fn ohash_next .
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.Pp
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.Fn ohash_lookup_interval
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and
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.Fn ohash_lookup_memory
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are the basic look-up element functions.
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The hashing function result is provided by the user as
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.Fa hv .
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These return a
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.Qq slot
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in the ohash table
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.Fa h ,
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to be used with
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.Fn ohash_find ,
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.Fn ohash_insert ,
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or
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.Fn ohash_remove .
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This slot is only valid up to the next call to
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.Fn ohash_insert
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or
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.Fn ohash_remove .
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.Pp
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.Fn ohash_lookup_interval
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handles string-like keys.
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.Fn ohash_lookup_interval
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assumes the key is the interval between
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.Fa start
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and
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.Fa end ,
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exclusive,
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though the actual elements stored in the table should only contain
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NUL-terminated keys.
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.Pp
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.Fn ohash_lookup_memory
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assumes the key is the memory area starting at
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.Fa k
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of size
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.Fa s .
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All bytes are significant in key comparison.
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.Pp
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.Fn ohash_find
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retrieves an element from a slot
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.Fa i
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returned by the
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.Fn ohash_lookup*
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functions.
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It returns
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.Dv NULL
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if the slot is empty.
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.Pp
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.Fn ohash_insert
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inserts a new element
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.Fa p
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at slot
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.Fa i .
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Slot
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.Fa i
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must be empty and element
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.Fa p
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must have a key corresponding to the
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.Fn ohash_lookup*
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call.
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.Pp
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.Fn ohash_remove
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removes the element at slot
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.Fa i .
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It returns the removed element, for user code to dispose of, or
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.Dv NULL
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if the slot was empty.
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.Pp
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.Fn ohash_first
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and
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.Fn ohash_next
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can be used to access all elements in an ohash table, like this:
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.Bd -literal -offset indent
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for (n = ohash_first(h, &i); n != NULL; n = ohash_next(h, &i))
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do_something_with(n);
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.Ed
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.Pp
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.Fa i
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points to an auxiliary unsigned integer used to record the current position
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in the ohash table.
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Those functions are safe to use even while entries are added to/removed
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from the table, but in such a case they don't guarantee that new entries
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will be returned.
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As a special case, they can safely be used to free elements in the table.
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.Pp
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.Fn ohash_entries
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returns the number of elements in the hash table.
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.Sh STORAGE HANDLING
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Only
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.Fn ohash_init ,
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.Fn ohash_insert ,
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.Fn ohash_remove
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and
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.Fn ohash_delete
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may call the user-supplied memory functions:
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.Bd -literal -offset indent
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p = (*info->calloc)(n, sizeof_record, info->data);
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/* copy data from old to p */
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(*info->free)(old, info->data);
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.Ed
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.Pp
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It is the responsibility of the user memory allocation code to verify
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that those calls did not fail.
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.Pp
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If memory allocation fails,
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.Fn ohash_init
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returns a useless hash table.
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.Fn ohash_insert
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and
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.Fn ohash_remove
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still perform the requested operation, but the returned table should be
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considered read-only.
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It can still be accessed by
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.Fn ohash_lookup* ,
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.Fn ohash_find ,
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.Fn ohash_first
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and
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.Fn ohash_next
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to dump relevant information to disk before aborting.
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.Sh THREAD SAFETY
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The open hashing functions are not thread-safe by design.
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In particular, in a threaded environment, there is no guarantee that a
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.Qq slot
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will not move between a
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.Fn ohash_lookup*
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and a
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.Fn ohash_find ,
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.Fn ohash_insert
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or
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.Fn ohash_remove
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call.
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.Pp
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Multi-threaded applications should explicitly protect ohash table access.
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.Sh SEE ALSO
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.Xr hcreate 3 ,
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.Xr ohash_interval 3
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.Rs
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.%A Donald E. Knuth
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.%B The Art of Computer Programming
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.%V Vol. 3
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.%P pp 506-550
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.%D 1973
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.Re
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.Sh STANDARDS
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Those functions are completely non-standard and should be avoided in
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portable programs.
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.Sh HISTORY
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Those functions were designed and written for
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.Ox
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.Xr make 1
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by Marc Espie in 1999.
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