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
5 * gquark.c: Functions for dealing with quarks and interned strings
7 * SPDX-License-Identifier: LGPL-2.1-or-later
9 * This library is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU Lesser General Public
11 * License as published by the Free Software Foundation; either
12 * version 2.1 of the License, or (at your option) any later version.
14 * This library is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * Lesser General Public License for more details.
19 * You should have received a copy of the GNU Lesser General Public
20 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
24 * Modified by the GLib Team and others 1997-2000. See the AUTHORS
25 * file for a list of people on the GLib Team. See the ChangeLog
26 * files for a list of changes. These files are distributed with
27 * GLib at ftp://ftp.gtk.org/pub/gtk/.
41 #include "gstrfuncs.h"
43 #include "gtestutils.h"
44 #include "glib_trace.h"
45 #include "glib-init.h"
47 #define QUARK_BLOCK_SIZE 2048
48 #define QUARK_STRING_BLOCK_SIZE (4096 - sizeof (gsize))
50 static inline GQuark quark_new (gchar *string);
52 G_LOCK_DEFINE_STATIC (quark_global);
53 static GHashTable *quark_ht = NULL;
54 static gchar **quarks = NULL;
55 static gint quark_seq_id = 0;
56 static gchar *quark_block = NULL;
57 static gint quark_block_offset = 0;
62 g_assert (quark_seq_id == 0);
63 quark_ht = g_hash_table_new (g_str_hash, g_str_equal);
64 quarks = g_new (gchar*, QUARK_BLOCK_SIZE);
72 * @short_description: a 2-way association between a string and a
73 * unique integer identifier
75 * Quarks are associations between strings and integer identifiers.
76 * Given either the string or the #GQuark identifier it is possible to
79 * Quarks are used for both [datasets][glib-Datasets] and
80 * [keyed data lists][glib-Keyed-Data-Lists].
82 * To create a new quark from a string, use g_quark_from_string() or
83 * g_quark_from_static_string().
85 * To find the string corresponding to a given #GQuark, use
86 * g_quark_to_string().
88 * To find the #GQuark corresponding to a given string, use
89 * g_quark_try_string().
91 * Another use for the string pool maintained for the quark functions
92 * is string interning, using g_intern_string() or
93 * g_intern_static_string(). An interned string is a canonical
94 * representation for a string. One important advantage of interned
95 * strings is that they can be compared for equality by a simple
96 * pointer comparison, rather than using strcmp().
102 * A GQuark is a non-zero integer which uniquely identifies a
103 * particular string. A GQuark value of zero is associated to %NULL.
108 * @QN: the name to return a #GQuark for
109 * @q_n: prefix for the function name
111 * A convenience macro which defines a function returning the
112 * #GQuark for the name @QN. The function will be named
115 * Note that the quark name will be stringified automatically
116 * in the macro, so you shouldn't use double quotes.
122 * g_quark_try_string:
123 * @string: (nullable): a string
125 * Gets the #GQuark associated with the given string, or 0 if string is
126 * %NULL or it has no associated #GQuark.
128 * If you want the GQuark to be created if it doesn't already exist,
129 * use g_quark_from_string() or g_quark_from_static_string().
131 * This function must not be used before library constructors have finished
134 * Returns: the #GQuark associated with the string, or 0 if @string is
135 * %NULL or there is no #GQuark associated with it
138 g_quark_try_string (const gchar *string)
145 G_LOCK (quark_global);
146 quark = GPOINTER_TO_UINT (g_hash_table_lookup (quark_ht, string));
147 G_UNLOCK (quark_global);
152 /* HOLDS: quark_global_lock */
154 quark_strdup (const gchar *string)
159 len = strlen (string) + 1;
161 /* For strings longer than half the block size, fall back
162 to strdup so that we fill our blocks at least 50%. */
163 if (len > QUARK_STRING_BLOCK_SIZE / 2)
164 return g_strdup (string);
166 if (quark_block == NULL ||
167 QUARK_STRING_BLOCK_SIZE - quark_block_offset < len)
169 quark_block = g_malloc (QUARK_STRING_BLOCK_SIZE);
170 quark_block_offset = 0;
173 copy = quark_block + quark_block_offset;
174 memcpy (copy, string, len);
175 quark_block_offset += len;
180 /* HOLDS: quark_global_lock */
182 quark_from_string (const gchar *string,
187 quark = GPOINTER_TO_UINT (g_hash_table_lookup (quark_ht, string));
191 quark = quark_new (duplicate ? quark_strdup (string) : (gchar *)string);
192 TRACE(GLIB_QUARK_NEW(string, quark));
199 quark_from_string_locked (const gchar *string,
207 G_LOCK (quark_global);
208 quark = quark_from_string (string, duplicate);
209 G_UNLOCK (quark_global);
215 * g_quark_from_string:
216 * @string: (nullable): a string
218 * Gets the #GQuark identifying the given string. If the string does
219 * not currently have an associated #GQuark, a new #GQuark is created,
220 * using a copy of the string.
222 * This function must not be used before library constructors have finished
223 * running. In particular, this means it cannot be used to initialize global
226 * Returns: the #GQuark identifying the string, or 0 if @string is %NULL
229 g_quark_from_string (const gchar *string)
231 return quark_from_string_locked (string, TRUE);
235 * g_quark_from_static_string:
236 * @string: (nullable): a string
238 * Gets the #GQuark identifying the given (static) string. If the
239 * string does not currently have an associated #GQuark, a new #GQuark
240 * is created, linked to the given string.
242 * Note that this function is identical to g_quark_from_string() except
243 * that if a new #GQuark is created the string itself is used rather
244 * than a copy. This saves memory, but can only be used if the string
245 * will continue to exist until the program terminates. It can be used
246 * with statically allocated strings in the main program, but not with
247 * statically allocated memory in dynamically loaded modules, if you
248 * expect to ever unload the module again (e.g. do not use this
249 * function in GTK+ theme engines).
251 * This function must not be used before library constructors have finished
252 * running. In particular, this means it cannot be used to initialize global
255 * Returns: the #GQuark identifying the string, or 0 if @string is %NULL
258 g_quark_from_static_string (const gchar *string)
260 return quark_from_string_locked (string, FALSE);
267 * Gets the string associated with the given #GQuark.
269 * Returns: the string associated with the #GQuark
272 g_quark_to_string (GQuark quark)
274 gchar* result = NULL;
278 seq_id = (guint) g_atomic_int_get (&quark_seq_id);
279 strings = g_atomic_pointer_get (&quarks);
282 result = strings[quark];
287 /* HOLDS: g_quark_global_lock */
289 quark_new (gchar *string)
294 if (quark_seq_id % QUARK_BLOCK_SIZE == 0)
296 quarks_new = g_new (gchar*, quark_seq_id + QUARK_BLOCK_SIZE);
297 if (quark_seq_id != 0)
298 memcpy (quarks_new, quarks, sizeof (char *) * quark_seq_id);
299 memset (quarks_new + quark_seq_id, 0, sizeof (char *) * QUARK_BLOCK_SIZE);
300 /* This leaks the old quarks array. Its unfortunate, but it allows
301 * us to do lockless lookup of the arrays, and there shouldn't be that
302 * many quarks in an app
304 g_atomic_pointer_set (&quarks, quarks_new);
307 quark = quark_seq_id;
308 g_atomic_pointer_set (&quarks[quark], string);
309 g_hash_table_insert (quark_ht, string, GUINT_TO_POINTER (quark));
310 g_atomic_int_inc (&quark_seq_id);
315 static inline const gchar *
316 quark_intern_string_locked (const gchar *string,
325 G_LOCK (quark_global);
326 quark = quark_from_string (string, duplicate);
327 result = quarks[quark];
328 G_UNLOCK (quark_global);
335 * @string: (nullable): a string
337 * Returns a canonical representation for @string. Interned strings
338 * can be compared for equality by comparing the pointers, instead of
341 * This function must not be used before library constructors have finished
342 * running. In particular, this means it cannot be used to initialize global
345 * Returns: a canonical representation for the string
350 g_intern_string (const gchar *string)
352 return quark_intern_string_locked (string, TRUE);
356 * g_intern_static_string:
357 * @string: (nullable): a static string
359 * Returns a canonical representation for @string. Interned strings
360 * can be compared for equality by comparing the pointers, instead of
361 * using strcmp(). g_intern_static_string() does not copy the string,
362 * therefore @string must not be freed or modified.
364 * This function must not be used before library constructors have finished
365 * running. In particular, this means it cannot be used to initialize global
368 * Returns: a canonical representation for the string
373 g_intern_static_string (const gchar *string)
375 return quark_intern_string_locked (string, FALSE);