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1 office 1 /* GLIB - Library of useful routines for C programming
2 * Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
3 * Copyright (C) 1998 Tim Janik
4 *
5 * gquark.c: Functions for dealing with quarks and interned strings
6 *
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2 of the License, or (at your option) any later version.
11 *
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
19 */
20  
21 /*
22 * Modified by the GLib Team and others 1997-2000. See the AUTHORS
23 * file for a list of people on the GLib Team. See the ChangeLog
24 * files for a list of changes. These files are distributed with
25 * GLib at ftp://ftp.gtk.org/pub/gtk/.
26 */
27  
28 /*
29 * MT safe
30 */
31  
32 #include "config.h"
33  
34 #include <string.h>
35  
36 #include "gslice.h"
37 #include "ghash.h"
38 #include "gquark.h"
39 #include "gstrfuncs.h"
40 #include "gthread.h"
41 #include "gtestutils.h"
42 #include "glib_trace.h"
43 #include "glib-init.h"
44  
45 #define QUARK_BLOCK_SIZE 2048
46 #define QUARK_STRING_BLOCK_SIZE (4096 - sizeof (gsize))
47  
48 static inline GQuark quark_new (gchar *string);
49  
50 G_LOCK_DEFINE_STATIC (quark_global);
51 static GHashTable *quark_ht = NULL;
52 static gchar **quarks = NULL;
53 static gint quark_seq_id = 0;
54 static gchar *quark_block = NULL;
55 static gint quark_block_offset = 0;
56  
57 void
58 g_quark_init (void)
59 {
60 g_assert (quark_seq_id == 0);
61 quark_ht = g_hash_table_new (g_str_hash, g_str_equal);
62 quarks = g_new (gchar*, QUARK_BLOCK_SIZE);
63 quarks[0] = NULL;
64 quark_seq_id = 1;
65 }
66  
67 /**
68 * SECTION:quarks
69 * @title: Quarks
70 * @short_description: a 2-way association between a string and a
71 * unique integer identifier
72 *
73 * Quarks are associations between strings and integer identifiers.
74 * Given either the string or the #GQuark identifier it is possible to
75 * retrieve the other.
76 *
77 * Quarks are used for both [datasets][glib-Datasets] and
78 * [keyed data lists][glib-Keyed-Data-Lists].
79 *
80 * To create a new quark from a string, use g_quark_from_string() or
81 * g_quark_from_static_string().
82 *
83 * To find the string corresponding to a given #GQuark, use
84 * g_quark_to_string().
85 *
86 * To find the #GQuark corresponding to a given string, use
87 * g_quark_try_string().
88 *
89 * Another use for the string pool maintained for the quark functions
90 * is string interning, using g_intern_string() or
91 * g_intern_static_string(). An interned string is a canonical
92 * representation for a string. One important advantage of interned
93 * strings is that they can be compared for equality by a simple
94 * pointer comparison, rather than using strcmp().
95 */
96  
97 /**
98 * GQuark:
99 *
100 * A GQuark is a non-zero integer which uniquely identifies a
101 * particular string. A GQuark value of zero is associated to %NULL.
102 */
103  
104 /**
105 * G_DEFINE_QUARK:
106 * @QN: the name to return a #GQuark for
107 * @q_n: prefix for the function name
108 *
109 * A convenience macro which defines a function returning the
110 * #GQuark for the name @QN. The function will be named
111 * @q_n_quark().
112 *
113 * Note that the quark name will be stringified automatically
114 * in the macro, so you shouldn't use double quotes.
115 *
116 * Since: 2.34
117 */
118  
119 /**
120 * g_quark_try_string:
121 * @string: (allow-none): a string
122 *
123 * Gets the #GQuark associated with the given string, or 0 if string is
124 * %NULL or it has no associated #GQuark.
125 *
126 * If you want the GQuark to be created if it doesn't already exist,
127 * use g_quark_from_string() or g_quark_from_static_string().
128 *
129 * Returns: the #GQuark associated with the string, or 0 if @string is
130 * %NULL or there is no #GQuark associated with it
131 */
132 GQuark
133 g_quark_try_string (const gchar *string)
134 {
135 GQuark quark = 0;
136  
137 if (string == NULL)
138 return 0;
139  
140 G_LOCK (quark_global);
141 quark = GPOINTER_TO_UINT (g_hash_table_lookup (quark_ht, string));
142 G_UNLOCK (quark_global);
143  
144 return quark;
145 }
146  
147 /* HOLDS: quark_global_lock */
148 static char *
149 quark_strdup (const gchar *string)
150 {
151 gchar *copy;
152 gsize len;
153  
154 len = strlen (string) + 1;
155  
156 /* For strings longer than half the block size, fall back
157 to strdup so that we fill our blocks at least 50%. */
158 if (len > QUARK_STRING_BLOCK_SIZE / 2)
159 return g_strdup (string);
160  
161 if (quark_block == NULL ||
162 QUARK_STRING_BLOCK_SIZE - quark_block_offset < len)
163 {
164 quark_block = g_malloc (QUARK_STRING_BLOCK_SIZE);
165 quark_block_offset = 0;
166 }
167  
168 copy = quark_block + quark_block_offset;
169 memcpy (copy, string, len);
170 quark_block_offset += len;
171  
172 return copy;
173 }
174  
175 /* HOLDS: quark_global_lock */
176 static inline GQuark
177 quark_from_string (const gchar *string,
178 gboolean duplicate)
179 {
180 GQuark quark = 0;
181  
182 quark = GPOINTER_TO_UINT (g_hash_table_lookup (quark_ht, string));
183  
184 if (!quark)
185 {
186 quark = quark_new (duplicate ? quark_strdup (string) : (gchar *)string);
187 TRACE(GLIB_QUARK_NEW(string, quark));
188 }
189  
190 return quark;
191 }
192  
193 /**
194 * g_quark_from_string:
195 * @string: (allow-none): a string
196 *
197 * Gets the #GQuark identifying the given string. If the string does
198 * not currently have an associated #GQuark, a new #GQuark is created,
199 * using a copy of the string.
200 *
201 * Returns: the #GQuark identifying the string, or 0 if @string is %NULL
202 */
203 GQuark
204 g_quark_from_string (const gchar *string)
205 {
206 GQuark quark;
207  
208 if (!string)
209 return 0;
210  
211 G_LOCK (quark_global);
212 quark = quark_from_string (string, TRUE);
213 G_UNLOCK (quark_global);
214  
215 return quark;
216 }
217  
218 /**
219 * g_quark_from_static_string:
220 * @string: (allow-none): a string
221 *
222 * Gets the #GQuark identifying the given (static) string. If the
223 * string does not currently have an associated #GQuark, a new #GQuark
224 * is created, linked to the given string.
225 *
226 * Note that this function is identical to g_quark_from_string() except
227 * that if a new #GQuark is created the string itself is used rather
228 * than a copy. This saves memory, but can only be used if the string
229 * will continue to exist until the program terminates. It can be used
230 * with statically allocated strings in the main program, but not with
231 * statically allocated memory in dynamically loaded modules, if you
232 * expect to ever unload the module again (e.g. do not use this
233 * function in GTK+ theme engines).
234 *
235 * Returns: the #GQuark identifying the string, or 0 if @string is %NULL
236 */
237 GQuark
238 g_quark_from_static_string (const gchar *string)
239 {
240 GQuark quark;
241  
242 if (!string)
243 return 0;
244  
245 G_LOCK (quark_global);
246 quark = quark_from_string (string, FALSE);
247 G_UNLOCK (quark_global);
248  
249 return quark;
250 }
251  
252 /**
253 * g_quark_to_string:
254 * @quark: a #GQuark.
255 *
256 * Gets the string associated with the given #GQuark.
257 *
258 * Returns: the string associated with the #GQuark
259 */
260 const gchar *
261 g_quark_to_string (GQuark quark)
262 {
263 gchar* result = NULL;
264 gchar **strings;
265 gint seq_id;
266  
267 seq_id = g_atomic_int_get (&quark_seq_id);
268 strings = g_atomic_pointer_get (&quarks);
269  
270 if (quark < seq_id)
271 result = strings[quark];
272  
273 return result;
274 }
275  
276 /* HOLDS: g_quark_global_lock */
277 static inline GQuark
278 quark_new (gchar *string)
279 {
280 GQuark quark;
281 gchar **quarks_new;
282  
283 if (quark_seq_id % QUARK_BLOCK_SIZE == 0)
284 {
285 quarks_new = g_new (gchar*, quark_seq_id + QUARK_BLOCK_SIZE);
286 if (quark_seq_id != 0)
287 memcpy (quarks_new, quarks, sizeof (char *) * quark_seq_id);
288 memset (quarks_new + quark_seq_id, 0, sizeof (char *) * QUARK_BLOCK_SIZE);
289 /* This leaks the old quarks array. Its unfortunate, but it allows
290 * us to do lockless lookup of the arrays, and there shouldn't be that
291 * many quarks in an app
292 */
293 g_atomic_pointer_set (&quarks, quarks_new);
294 }
295  
296 quark = quark_seq_id;
297 g_atomic_pointer_set (&quarks[quark], string);
298 g_hash_table_insert (quark_ht, string, GUINT_TO_POINTER (quark));
299 g_atomic_int_inc (&quark_seq_id);
300  
301 return quark;
302 }
303  
304 /**
305 * g_intern_string:
306 * @string: (allow-none): a string
307 *
308 * Returns a canonical representation for @string. Interned strings
309 * can be compared for equality by comparing the pointers, instead of
310 * using strcmp().
311 *
312 * Returns: a canonical representation for the string
313 *
314 * Since: 2.10
315 */
316 const gchar *
317 g_intern_string (const gchar *string)
318 {
319 const gchar *result;
320 GQuark quark;
321  
322 if (!string)
323 return NULL;
324  
325 G_LOCK (quark_global);
326 quark = quark_from_string (string, TRUE);
327 result = quarks[quark];
328 G_UNLOCK (quark_global);
329  
330 return result;
331 }
332  
333 /**
334 * g_intern_static_string:
335 * @string: (allow-none): a static string
336 *
337 * Returns a canonical representation for @string. Interned strings
338 * can be compared for equality by comparing the pointers, instead of
339 * using strcmp(). g_intern_static_string() does not copy the string,
340 * therefore @string must not be freed or modified.
341 *
342 * Returns: a canonical representation for the string
343 *
344 * Since: 2.10
345 */
346 const gchar *
347 g_intern_static_string (const gchar *string)
348 {
349 GQuark quark;
350 const gchar *result;
351  
352 if (!string)
353 return NULL;
354  
355 G_LOCK (quark_global);
356 quark = quark_from_string (string, FALSE);
357 result = quarks[quark];
358 G_UNLOCK (quark_global);
359  
360 return result;
361 }