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