4 * Userspace RCU library - sys_futex compatibility code
6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with this library; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
30 #include <urcu/arch.h>
31 #include <urcu/assert.h>
32 #include <urcu/futex.h>
33 #include <urcu/system.h>
36 * Using attribute "weak" for __urcu_compat_futex_lock and
37 * __urcu_compat_futex_cond. Those are globally visible by the entire
38 * program, even though many shared objects may have their own version.
39 * The first version that gets loaded will be used by the entire program
40 * (executable and all shared objects).
44 pthread_mutex_t __urcu_compat_futex_lock
= PTHREAD_MUTEX_INITIALIZER
;
46 pthread_cond_t __urcu_compat_futex_cond
= PTHREAD_COND_INITIALIZER
;
49 * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
50 * For now, timeout, uaddr2 and val3 are unused.
51 * Waiter will relinquish the CPU until woken up.
54 int compat_futex_noasync(int32_t *uaddr
, int op
, int32_t val
,
55 const struct timespec
*timeout
, int32_t *uaddr2
, int32_t val3
)
60 * Check if NULL. Don't let users expect that they are taken into
63 urcu_posix_assert(!timeout
);
64 urcu_posix_assert(!uaddr2
);
65 urcu_posix_assert(!val3
);
68 * memory barriers to serialize with the previous uaddr modification.
72 lockret
= pthread_mutex_lock(&__urcu_compat_futex_lock
);
81 * Wait until *uaddr is changed to something else than "val".
82 * Comparing *uaddr content against val figures out which
83 * thread has been awakened.
85 while (CMM_LOAD_SHARED(*uaddr
) == val
)
86 pthread_cond_wait(&__urcu_compat_futex_cond
,
87 &__urcu_compat_futex_lock
);
91 * Each wake is sending a broadcast, thus attempting wakeup of
92 * all awaiting threads, independently of their respective
95 pthread_cond_broadcast(&__urcu_compat_futex_cond
);
101 lockret
= pthread_mutex_unlock(&__urcu_compat_futex_lock
);
111 * _ASYNC SIGNAL-SAFE_.
112 * For now, timeout, uaddr2 and val3 are unused.
113 * Waiter will busy-loop trying to read the condition.
114 * It is OK to use compat_futex_async() on a futex address on which
115 * futex() WAKE operations are also performed.
118 int compat_futex_async(int32_t *uaddr
, int op
, int32_t val
,
119 const struct timespec
*timeout
, int32_t *uaddr2
, int32_t val3
)
124 * Check if NULL. Don't let users expect that they are taken into
127 urcu_posix_assert(!timeout
);
128 urcu_posix_assert(!uaddr2
);
129 urcu_posix_assert(!val3
);
132 * Ensure previous memory operations on uaddr have completed.
138 while (CMM_LOAD_SHARED(*uaddr
) == val
) {
139 if (poll(NULL
, 0, 10) < 0) {
141 /* Keep poll errno. Caller handles EINTR. */