2 * Copyright © 2008 Ryan Lortie
3 * Copyright © 2010 Codethink Limited
5 * This library is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU Lesser General Public
7 * License as published by the Free Software Foundation; either
8 * version 2 of the licence, or (at your option) any later version.
10 * This library is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * Lesser General Public License for more details.
15 * You should have received a copy of the GNU Lesser General Public
16 * License along with this library; if not, write to the
17 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
18 * Boston, MA 02111-1307, USA.
20 * Author: Ryan Lortie <desrt@desrt.ca>
25 #include <glib/gatomic.h>
26 #include <glib/gslist.h>
27 #include <glib/gthread.h>
29 #include "gthreadprivate.h"
34 #ifdef G_BIT_LOCK_FORCE_FUTEX_EMULATION
39 static GSList *g_futex_address_list = NULL;
40 static GMutex *g_futex_mutex = NULL;
44 _g_futex_thread_init (void) {
46 g_futex_mutex = g_mutex_new ();
52 * We have headers for futex(2) on the build machine. This does not
53 * imply that every system that ever runs the resulting glib will have
54 * kernel support for futex, but you'd have to have a pretty old
55 * kernel in order for that not to be the case.
57 * If anyone actually gets bit by this, please file a bug. :)
59 #include <linux/futex.h>
65 * @address: a pointer to an integer
66 * @value: the value that should be at @address
68 * Atomically checks that the value stored at @address is equal to
69 * @value and then blocks. If the value stored at @address is not
70 * equal to @value then this function returns immediately.
72 * To unblock, call g_futex_wake() on @address.
74 * This call may spuriously unblock (for example, in response to the
75 * process receiving a signal) but this is not guaranteed. Unlike the
76 * Linux system call of a similar name, there is no guarantee that a
77 * waiting process will unblock due to a g_futex_wake() call in a
81 g_futex_wait (const volatile gint *address,
84 syscall (SYS_futex, address, (gsize) FUTEX_WAIT, (gsize) value, NULL);
89 * @address: a pointer to an integer
91 * Nominally, wakes one thread that is blocked in g_futex_wait() on
92 * @address (if any thread is currently waiting).
94 * As mentioned in the documention for g_futex_wait(), spurious
95 * wakeups may occur. As such, this call may result in more than one
96 * thread being woken up.
99 g_futex_wake (const volatile gint *address)
101 syscall (SYS_futex, address, (gsize) FUTEX_WAKE, (gsize) 1, NULL);
106 /* emulate futex(2) */
109 const volatile gint *address;
114 static GSList *g_futex_address_list;
115 static GMutex *g_futex_mutex;
118 g_futex_find_address (const volatile gint *address)
122 for (node = g_futex_address_list; node; node = node->next)
124 WaitAddress *waiter = node->data;
126 if (waiter->address == address)
134 g_futex_wait (const volatile gint *address,
137 g_mutex_lock (g_futex_mutex);
138 if G_LIKELY (g_atomic_int_get (address) == value)
142 if ((waiter = g_futex_find_address (address)) == NULL)
144 waiter = g_slice_new (WaitAddress);
145 waiter->address = address;
146 waiter->wait_queue = g_cond_new ();
147 waiter->ref_count = 0;
148 g_futex_address_list =
149 g_slist_prepend (g_futex_address_list, waiter);
153 g_cond_wait (waiter->wait_queue, g_futex_mutex);
155 if (!--waiter->ref_count)
157 g_futex_address_list =
158 g_slist_remove (g_futex_address_list, waiter);
159 g_cond_free (waiter->wait_queue);
160 g_slice_free (WaitAddress, waiter);
163 g_mutex_unlock (g_futex_mutex);
167 g_futex_wake (const volatile gint *address)
171 /* need to lock here for two reasons:
172 * 1) need to acquire/release lock to ensure waiter is not in
173 * the process of registering a wait
174 * 2) need to -stay- locked until the end to ensure a wake()
175 * in another thread doesn't cause 'waiter' to stop existing
177 g_mutex_lock (g_futex_mutex);
178 if ((waiter = g_futex_find_address (address)))
179 g_cond_signal (waiter->wait_queue);
180 g_mutex_unlock (g_futex_mutex);
184 #define CONTENTION_CLASSES 11
185 static volatile gint g_bit_lock_contended[CONTENTION_CLASSES];
189 * @address: a pointer to an integer
190 * @lock_bit: a bit value between 0 and 31
192 * Sets the indicated @lock_bit in @address. If the bit is already
193 * set, this call will block until g_bit_unlock() unsets the
196 * Attempting to lock on two different bits within the same integer is
197 * not supported and will very probably cause deadlocks.
199 * The value of the bit that is set is (1u << @bit). If @bit is not
200 * between 0 and 31 then the result is undefined.
202 * This function accesses @address atomically. All other accesses to
203 * @address must be atomic in order for this function to work
207 g_bit_lock (volatile gint *address,
213 v = g_atomic_int_get (address);
214 if (v & (1u << lock_bit))
217 guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
219 g_atomic_int_add (&g_bit_lock_contended[class], +1);
220 g_futex_wait (address, v);
221 g_atomic_int_add (&g_bit_lock_contended[class], -1);
226 if (!g_atomic_int_compare_and_exchange (address, v, v | (1u << lock_bit)))
232 * @address: a pointer to an integer
233 * @lock_bit: a bit value between 0 and 31
235 * Sets the indicated @lock_bit in @address, returning %TRUE if
236 * successful. If the bit is already set, returns %FALSE immediately.
238 * Attempting to lock on two different bits within the same integer is
241 * The value of the bit that is set is (1u << @bit). If @bit is not
242 * between 0 and 31 then the result is undefined.
244 * This function accesses @address atomically. All other accesses to
245 * @address must be atomic in order for this function to work
249 g_bit_trylock (volatile gint *address,
255 v = g_atomic_int_get (address);
256 if (v & (1u << lock_bit))
260 if (!g_atomic_int_compare_and_exchange (address, v, v | (1u << lock_bit)))
268 * @address: a pointer to an integer
269 * @lock_bit: a bit value between 0 and 31
271 * Clears the indicated @lock_bit in @address. If another thread is
272 * currently blocked in g_bit_lock() on this same bit then it will be
275 * This function accesses @address atomically. All other accesses to
276 * @address must be atomic in order for this function to work
280 g_bit_unlock (volatile gint *address,
283 guint class = ((gsize) address) % G_N_ELEMENTS (g_bit_lock_contended);
287 v = g_atomic_int_get (address);
288 if (!g_atomic_int_compare_and_exchange (address, v, v & ~(1u << lock_bit)))
291 if (g_atomic_int_get (&g_bit_lock_contended[class]))
292 g_futex_wake (address);
295 #define __G_BITLOCK_C__
296 #include "galiasdef.c"