1OPENSSL_LH_COMPFUNC(3ossl) OpenSSL OPENSSL_LH_COMPFUNC(3ossl)
2
6 LHASH, DECLARE_LHASH_OF, OPENSSL_LH_COMPFUNC, OPENSSL_LH_HASHFUNC,
7 OPENSSL_LH_DOALL_FUNC, LHASH_DOALL_ARG_FN_TYPE,
8 IMPLEMENT_LHASH_HASH_FN, IMPLEMENT_LHASH_COMP_FN, lh_TYPE_new,
9 lh_TYPE_free, lh_TYPE_flush, lh_TYPE_insert, lh_TYPE_delete,
10 lh_TYPE_retrieve, lh_TYPE_doall, lh_TYPE_doall_arg, lh_TYPE_error,
11 OPENSSL_LH_new, OPENSSL_LH_free, OPENSSL_LH_flush, OPENSSL_LH_insert,
12 OPENSSL_LH_delete, OPENSSL_LH_retrieve, OPENSSL_LH_doall,
13 OPENSSL_LH_doall_arg, OPENSSL_LH_error - dynamic hash table
14
16 #include <openssl/lhash.h>
17 DECLARE_LHASH_OF(TYPE);
19 LHASH_OF(TYPE) *lh_TYPE_new(OPENSSL_LH_HASHFUNC hash, OPENSSL_LH_COMPFUNC compare);
21 void lh_TYPE_free(LHASH_OF(TYPE) *table);
22 void lh_TYPE_flush(LHASH_OF(TYPE) *table);
23 TYPE *lh_TYPE_insert(LHASH_OF(TYPE) *table, TYPE *data);
25 TYPE *lh_TYPE_delete(LHASH_OF(TYPE) *table, TYPE *data);
26 TYPE *lh_retrieve(LHASH_OF(TYPE) *table, TYPE *data);
27 void lh_TYPE_doall(LHASH_OF(TYPE) *table, OPENSSL_LH_DOALL_FUNC func);
29 void lh_TYPE_doall_arg(LHASH_OF(TYPE) *table, OPENSSL_LH_DOALL_FUNCARG func,
30 TYPE *arg);
31 int lh_TYPE_error(LHASH_OF(TYPE) *table);
33 typedef int (*OPENSSL_LH_COMPFUNC)(const void *, const void *);
35 typedef unsigned long (*OPENSSL_LH_HASHFUNC)(const void *);
36 typedef void (*OPENSSL_LH_DOALL_FUNC)(const void *);
37 typedef void (*LHASH_DOALL_ARG_FN_TYPE)(const void *, const void *);
38 OPENSSL_LHASH *OPENSSL_LH_new(OPENSSL_LH_HASHFUNC h, OPENSSL_LH_COMPFUNC c);
40 void OPENSSL_LH_free(OPENSSL_LHASH *lh);
41 void OPENSSL_LH_flush(OPENSSL_LHASH *lh);
42 void *OPENSSL_LH_insert(OPENSSL_LHASH *lh, void *data);
44 void *OPENSSL_LH_delete(OPENSSL_LHASH *lh, const void *data);
45 void *OPENSSL_LH_retrieve(OPENSSL_LHASH *lh, const void *data);
46 void OPENSSL_LH_doall(OPENSSL_LHASH *lh, OPENSSL_LH_DOALL_FUNC func);
48 void OPENSSL_LH_doall_arg(OPENSSL_LHASH *lh, OPENSSL_LH_DOALL_FUNCARG func, void *arg);
49 int OPENSSL_LH_error(OPENSSL_LHASH *lh);
51
53 This library implements type-checked dynamic hash tables. The hash
54 table entries can be arbitrary structures. Usually they consist of key
55 and value fields. In the description here, TYPE is used a placeholder
56 for any of the OpenSSL datatypes, such as SSL_SESSION.
57 lh_TYPE_new() creates a new LHASH_OF(TYPE) structure to store arbitrary
59 data entries, and specifies the 'hash' and 'compare' callbacks to be
60 used in organising the table's entries. The hash callback takes a
61 pointer to a table entry as its argument and returns an unsigned long
62 hash value for its key field. The hash value is normally truncated to
63 a power of 2, so make sure that your hash function returns well mixed
64 low order bits. The compare callback takes two arguments (pointers to
65 two hash table entries), and returns 0 if their keys are equal, nonzero
66 otherwise.
67 If your hash table will contain items of some particular type and the
69 hash and compare callbacks hash/compare these types, then the
70 IMPLEMENT_LHASH_HASH_FN and IMPLEMENT_LHASH_COMP_FN macros can be used
71 to create callback wrappers of the prototypes required by lh_TYPE_new()
72 as shown in this example:
73 /*
75 * Implement the hash and compare functions; "stuff" can be any word.
76 */
77 static unsigned long stuff_hash(const TYPE *a)
78 {
79 ...
80 }
81 static int stuff_cmp(const TYPE *a, const TYPE *b)
82 {
83 ...
84 }
85 /*
87 * Implement the wrapper functions.
88 */
89 static IMPLEMENT_LHASH_HASH_FN(stuff, TYPE)
90 static IMPLEMENT_LHASH_COMP_FN(stuff, TYPE)
91 If the type is going to be used in several places, the following macros
93 can be used in a common header file to declare the function wrappers:
94 DECLARE_LHASH_HASH_FN(stuff, TYPE)
96 DECLARE_LHASH_COMP_FN(stuff, TYPE)
97 Then a hash table of TYPE objects can be created using this:
99 LHASH_OF(TYPE) *htable;
101 htable = B<lh_I<TYPE>_new>(LHASH_HASH_FN(stuff), LHASH_COMP_FN(stuff));
103 lh_TYPE_free() frees the LHASH_OF(TYPE) structure table. Allocated hash
105 table entries will not be freed; consider using lh_TYPE_doall() to
106 deallocate any remaining entries in the hash table (see below).
107 lh_TYPE_flush() empties the LHASH_OF(TYPE) structure table. New entries
109 can be added to the flushed table. Allocated hash table entries will
110 not be freed; consider using lh_TYPE_doall() to deallocate any
111 remaining entries in the hash table (see below).
112 lh_TYPE_insert() inserts the structure pointed to by data into table.
114 If there already is an entry with the same key, the old value is
115 replaced. Note that lh_TYPE_insert() stores pointers, the data are not
116 copied.
117 lh_TYPE_delete() deletes an entry from table.
119 lh_TYPE_retrieve() looks up an entry in table. Normally, data is a
121 structure with the key field(s) set; the function will return a pointer
122 to a fully populated structure.
123 lh_TYPE_doall() will, for every entry in the hash table, call func with
125 the data item as its parameter. For example:
126 /* Cleans up resources belonging to 'a' (this is implemented elsewhere) */
128 void TYPE_cleanup_doall(TYPE *a);
129 /* Implement a prototype-compatible wrapper for "TYPE_cleanup" */
131 IMPLEMENT_LHASH_DOALL_FN(TYPE_cleanup, TYPE)
132 /* Call "TYPE_cleanup" against all items in a hash table. */
134 lh_TYPE_doall(hashtable, LHASH_DOALL_FN(TYPE_cleanup));
135 /* Then the hash table itself can be deallocated */
137 lh_TYPE_free(hashtable);
138 When doing this, be careful if you delete entries from the hash table
140 in your callbacks: the table may decrease in size, moving the item that
141 you are currently on down lower in the hash table - this could cause
142 some entries to be skipped during the iteration. The second best
143 solution to this problem is to set hash->down_load=0 before you start
144 (which will stop the hash table ever decreasing in size). The best
145 solution is probably to avoid deleting items from the hash table inside
146 a "doall" callback!
147 lh_TYPE_doall_arg() is the same as lh_TYPE_doall() except that func
149 will be called with arg as the second argument and func should be of
150 type LHASH_DOALL_ARG_FN(TYPE) (a callback prototype that is passed both
151 the table entry and an extra argument). As with lh_doall(), you can
152 instead choose to declare your callback with a prototype matching the
153 types you are dealing with and use the declare/implement macros to
154 create compatible wrappers that cast variables before calling your
155 type-specific callbacks. An example of this is demonstrated here
156 (printing all hash table entries to a BIO that is provided by the
157 caller):
158 /* Prints item 'a' to 'output_bio' (this is implemented elsewhere) */
160 void TYPE_print_doall_arg(const TYPE *a, BIO *output_bio);
161 /* Implement a prototype-compatible wrapper for "TYPE_print" */
163 static IMPLEMENT_LHASH_DOALL_ARG_FN(TYPE, const TYPE, BIO)
164 /* Print out the entire hashtable to a particular BIO */
166 lh_TYPE_doall_arg(hashtable, LHASH_DOALL_ARG_FN(TYPE_print), BIO,
167 logging_bio);
168 lh_TYPE_error() can be used to determine if an error occurred in the
170 last operation.
171 OPENSSL_LH_new() is the same as the lh_TYPE_new() except that it is not
173 type specific. So instead of returning an LHASH_OF(TYPE) value it
174 returns a void *. In the same way the functions OPENSSL_LH_free(),
175 OPENSSL_LH_flush(), OPENSSL_LH_insert(), OPENSSL_LH_delete(),
176 OPENSSL_LH_retrieve(), OPENSSL_LH_doall(), OPENSSL_LH_doall_arg(), and
177 OPENSSL_LH_error() are equivalent to the similarly named lh_TYPE
178 functions except that they return or use a void * where the equivalent
179 lh_TYPE function returns or uses a TYPE * or LHASH_OF(TYPE) *. lh_TYPE
180 functions are implemented as type checked wrappers around the
181 OPENSSL_LH functions. Most applications should not call the OPENSSL_LH
182 functions directly.
183
185 lh_TYPE_new() and OPENSSL_LH_new() return NULL on error, otherwise a
186 pointer to the new LHASH structure.
187 When a hash table entry is replaced, lh_TYPE_insert() or
189 OPENSSL_LH_insert() return the value being replaced. NULL is returned
190 on normal operation and on error.
191 lh_TYPE_delete() and OPENSSL_LH_delete() return the entry being
193 deleted. NULL is returned if there is no such value in the hash table.
194 lh_TYPE_retrieve() and OPENSSL_LH_retrieve() return the hash table
196 entry if it has been found, NULL otherwise.
197 lh_TYPE_error() and OPENSSL_LH_error() return 1 if an error occurred in
199 the last operation, 0 otherwise. It's meaningful only after non-
200 retrieve operations.
201 lh_TYPE_free(), OPENSSL_LH_free(), lh_TYPE_flush(), OPENSSL_LH_flush(),
203 lh_TYPE_doall() OPENSSL_LH_doall(), lh_TYPE_doall_arg() and
204 OPENSSL_LH_doall_arg() return no values.
205
207 The LHASH code is not thread safe. All updating operations, as well as
208 lh_TYPE_error() or OPENSSL_LH_error() calls must be performed under a
209 write lock. All retrieve operations should be performed under a read
210 lock, unless accurate usage statistics are desired. In which case, a
211 write lock should be used for retrieve operations as well. For output
212 of the usage statistics, using the functions from OPENSSL_LH_stats(3),
213 a read lock suffices.
214 The LHASH code regards table entries as constant data. As such, it
216 internally represents lh_insert()'d items with a "const void *" pointer
217 type. This is why callbacks such as those used by lh_doall() and
218 lh_doall_arg() declare their prototypes with "const", even for the
219 parameters that pass back the table items' data pointers - for
220 consistency, user-provided data is "const" at all times as far as the
221 LHASH code is concerned. However, as callers are themselves providing
222 these pointers, they can choose whether they too should be treating all
223 such parameters as constant.
224 As an example, a hash table may be maintained by code that, for reasons
226 of encapsulation, has only "const" access to the data being indexed in
227 the hash table (i.e. it is returned as "const" from elsewhere in their
228 code) - in this case the LHASH prototypes are appropriate as-is.
229 Conversely, if the caller is responsible for the life-time of the data
230 in question, then they may well wish to make modifications to table
231 item passed back in the lh_doall() or lh_doall_arg() callbacks (see the
232 "TYPE_cleanup" example above). If so, the caller can either cast the
233 "const" away (if they're providing the raw callbacks themselves) or use
234 the macros to declare/implement the wrapper functions without "const"
235 types.
236 Callers that only have "const" access to data they're indexing in a
238 table, yet declare callbacks without constant types (or cast the
239 "const" away themselves), are therefore creating their own risks/bugs
240 without being encouraged to do so by the API. On a related note, those
241 auditing code should pay special attention to any instances of
242 DECLARE/IMPLEMENT_LHASH_DOALL_[ARG_]_FN macros that provide types
243 without any "const" qualifiers.
244
246 lh_TYPE_insert() and OPENSSL_LH_insert() return NULL both for success
247 and error.
248
250 OPENSSL_LH_stats(3)
251
253 In OpenSSL 1.0.0, the lhash interface was revamped for better type
254 checking.
255
257 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
258 Licensed under the Apache License 2.0 (the "License"). You may not use
260 this file except in compliance with the License. You can obtain a copy
261 in the file LICENSE in the source distribution or at
262 <https://www.openssl.org/source/license.html>.
2633.0.5 2022-07-05 OPENSSL_LH_COMPFUNC(3ossl)