7 * Userspace RCU header.
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
10 * dynamically with the userspace rcu library.
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
15 * This library is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU Lesser General Public
17 * License as published by the Free Software Foundation; either
18 * version 2.1 of the License, or (at your option) any later version.
20 * This library is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * Lesser General Public License for more details.
25 * You should have received a copy of the GNU Lesser General Public
26 * License along with this library; if not, write to the Free Software
27 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
37 #include <urcu/compiler.h>
38 #include <urcu/arch.h>
39 #include <urcu/system.h>
40 #include <urcu/uatomic_arch.h>
41 #include <urcu/list.h>
43 #define futex(...) syscall(__NR_futex, __VA_ARGS__)
48 * This code section can only be included in LGPL 2.1 compatible source code.
49 * See below for the function call wrappers which can be used in code meant to
50 * be only linked with the Userspace RCU library. This comes with a small
51 * performance degradation on the read-side due to the added function calls.
52 * This is required to permit relinking with newer versions of the library.
56 * The signal number used by the RCU library can be overridden with
57 * -DSIGURCU= when compiling the library.
60 #define SIGURCU SIGUSR1
64 * If a reader is really non-cooperative and refuses to commit its
65 * urcu_active_readers count to memory (there is no barrier in the reader
66 * per-se), kick it after a few loops waiting for it.
68 #define KICK_READER_LOOPS 10000
71 * Active attempts to check for reader Q.S. before calling futex().
73 #define RCU_QS_ACTIVE_ATTEMPTS 100
76 #define rcu_assert(args...) assert(args)
78 #define rcu_assert(args...)
87 #define YIELD_READ (1 << 0)
88 #define YIELD_WRITE (1 << 1)
91 * Updates without URCU_MB are much slower. Account this in
95 /* maximum sleep delay, in us */
98 #define MAX_SLEEP 30000
101 extern unsigned int yield_active
;
102 extern unsigned int __thread rand_yield
;
104 static inline void debug_yield_read(void)
106 if (yield_active
& YIELD_READ
)
107 if (rand_r(&rand_yield
) & 0x1)
108 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
111 static inline void debug_yield_write(void)
113 if (yield_active
& YIELD_WRITE
)
114 if (rand_r(&rand_yield
) & 0x1)
115 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
118 static inline void debug_yield_init(void)
120 rand_yield
= time(NULL
) ^ pthread_self();
123 static inline void debug_yield_read(void)
127 static inline void debug_yield_write(void)
131 static inline void debug_yield_init(void)
138 static inline void reader_barrier()
143 static inline void reader_barrier()
150 * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
151 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
153 #define RCU_GP_COUNT (1UL << 0)
154 /* Use the amount of bits equal to half of the architecture long size */
155 #define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
156 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
159 * Global quiescent period counter with low-order bits unused.
160 * Using a int rather than a char to eliminate false register dependencies
161 * causing stalls on some architectures.
163 extern long urcu_gp_ctr
;
166 /* Data used by both reader and synchronize_rcu() */
169 /* Data used for registry */
170 struct list_head head
__attribute__((aligned(CACHE_LINE_SIZE
)));
174 extern struct urcu_reader __thread urcu_reader
;
179 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
181 static inline void wake_up_gp(void)
183 if (unlikely(uatomic_read(&gp_futex
) == -1)) {
184 uatomic_set(&gp_futex
, 0);
185 futex(&gp_futex
, FUTEX_WAKE
, 1,
190 static inline int rcu_old_gp_ongoing(long *value
)
197 * Make sure both tests below are done on the same version of *value
198 * to insure consistency.
200 v
= LOAD_SHARED(*value
);
201 return (v
& RCU_GP_CTR_NEST_MASK
) &&
202 ((v
^ urcu_gp_ctr
) & RCU_GP_CTR_BIT
);
205 static inline void _rcu_read_lock(void)
209 tmp
= urcu_reader
.ctr
;
210 /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
211 if (likely(!(tmp
& RCU_GP_CTR_NEST_MASK
))) {
212 _STORE_SHARED(urcu_reader
.ctr
, _LOAD_SHARED(urcu_gp_ctr
));
214 * Set active readers count for outermost nesting level before
215 * accessing the pointer. See force_mb_all_threads().
219 _STORE_SHARED(urcu_reader
.ctr
, tmp
+ RCU_GP_COUNT
);
223 static inline void _rcu_read_unlock(void)
227 tmp
= urcu_reader
.ctr
;
229 * Finish using rcu before decrementing the pointer.
230 * See force_mb_all_threads().
232 if (likely((tmp
& RCU_GP_CTR_NEST_MASK
) == RCU_GP_COUNT
)) {
234 _STORE_SHARED(urcu_reader
.ctr
, urcu_reader
.ctr
- RCU_GP_COUNT
);
235 /* write urcu_reader.ctr before read futex */
239 _STORE_SHARED(urcu_reader
.ctr
, urcu_reader
.ctr
- RCU_GP_COUNT
);
243 #endif /* _URCU_STATIC_H */