7 * Userspace RCU header.
9 * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
10 * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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.h>
41 #include <urcu/list.h>
42 #include <urcu/futex.h>
43 #include <urcu/tls-compat.h>
49 /* Default is RCU_MEMBARRIER */
50 #if !defined(RCU_MEMBARRIER) && !defined(RCU_MB) && !defined(RCU_SIGNAL)
51 #define RCU_MEMBARRIER
55 * RCU_MEMBARRIER is only possibly available on Linux. Fallback to RCU_MB
58 #if !defined(__linux__) && defined(RCU_MEMBARRIER)
64 * The ABI of sys_membarrier changed after its original implementation.
65 * Disable it for now. Use RCU_MB flavor instead.
73 * This code section can only be included in LGPL 2.1 compatible source code.
74 * See below for the function call wrappers which can be used in code meant to
75 * be only linked with the Userspace RCU library. This comes with a small
76 * performance degradation on the read-side due to the added function calls.
77 * This is required to permit relinking with newer versions of the library.
81 * The signal number used by the RCU library can be overridden with
82 * -DSIGRCU= when compiling the library.
83 * Provide backward compatibility for liburcu 0.3.x SIGURCU.
86 #define SIGRCU SIGURCU
90 #define SIGRCU SIGUSR1
94 #define rcu_assert(args...) assert(args)
96 #define rcu_assert(args...)
105 #define YIELD_READ (1 << 0)
106 #define YIELD_WRITE (1 << 1)
109 * Updates with RCU_SIGNAL are much slower. Account this in the delay.
112 /* maximum sleep delay, in us */
113 #define MAX_SLEEP 30000
118 extern unsigned int yield_active
;
119 extern DECLARE_URCU_TLS(unsigned int, rand_yield
);
121 static inline void debug_yield_read(void)
123 if (yield_active
& YIELD_READ
)
124 if (rand_r(&URCU_TLS(rand_yield
)) & 0x1)
125 usleep(rand_r(&URCU_TLS(rand_yield
)) % MAX_SLEEP
);
128 static inline void debug_yield_write(void)
130 if (yield_active
& YIELD_WRITE
)
131 if (rand_r(&URCU_TLS(rand_yield
)) & 0x1)
132 usleep(rand_r(&URCU_TLS(rand_yield
)) % MAX_SLEEP
);
135 static inline void debug_yield_init(void)
137 URCU_TLS(rand_yield
) = time(NULL
) ^ (unsigned long) pthread_self();
140 static inline void debug_yield_read(void)
144 static inline void debug_yield_write(void)
148 static inline void debug_yield_init(void)
155 * RCU memory barrier broadcast group. Currently, only broadcast to all process
156 * threads is supported (group 0).
158 * Slave barriers are only guaranteed to be ordered wrt master barriers.
160 * The pair ordering is detailed as (O: ordered, X: not ordered) :
166 #define MB_GROUP_ALL 0
167 #define RCU_MB_GROUP MB_GROUP_ALL
169 #ifdef RCU_MEMBARRIER
170 extern int has_sys_membarrier
;
172 static inline void smp_mb_slave(int group
)
174 if (caa_likely(has_sys_membarrier
))
182 static inline void smp_mb_slave(int group
)
189 static inline void smp_mb_slave(int group
)
196 * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use
197 * a full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
199 #define RCU_GP_COUNT (1UL << 0)
200 /* Use the amount of bits equal to half of the architecture long size */
201 #define RCU_GP_CTR_PHASE (1UL << (sizeof(unsigned long) << 2))
202 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_PHASE - 1)
205 * Global quiescent period counter with low-order bits unused.
206 * Using a int rather than a char to eliminate false register dependencies
207 * causing stalls on some architectures.
209 extern unsigned long rcu_gp_ctr
;
212 /* Data used by both reader and synchronize_rcu() */
215 /* Data used for registry */
216 struct cds_list_head node
__attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
220 extern DECLARE_URCU_TLS(struct rcu_reader
, rcu_reader
);
222 extern int32_t gp_futex
;
225 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
227 static inline void wake_up_gp(void)
229 if (caa_unlikely(uatomic_read(&gp_futex
) == -1)) {
230 uatomic_set(&gp_futex
, 0);
232 * Ignoring return value until we can make this function
233 * return something (because urcu_die() is not publicly
236 (void) futex_async(&gp_futex
, FUTEX_WAKE
, 1,
241 static inline int rcu_gp_ongoing(unsigned long *ctr
)
246 * Make sure both tests below are done on the same version of *value
247 * to insure consistency.
249 v
= CMM_LOAD_SHARED(*ctr
);
250 return (v
& RCU_GP_CTR_NEST_MASK
) &&
251 ((v
^ rcu_gp_ctr
) & RCU_GP_CTR_PHASE
);
255 * Helper for _rcu_read_lock(). The format of rcu_gp_ctr (as well as
256 * the per-thread rcu_reader.ctr) has the upper bits containing a count of
257 * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
258 * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in
259 * _rcu_read_lock() happen before the subsequent read-side critical section.
261 static inline void _rcu_read_lock_update(unsigned long tmp
)
263 if (caa_likely(!(tmp
& RCU_GP_CTR_NEST_MASK
))) {
264 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
).ctr
, _CMM_LOAD_SHARED(rcu_gp_ctr
));
265 smp_mb_slave(RCU_MB_GROUP
);
267 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
).ctr
, tmp
+ RCU_GP_COUNT
);
271 * Enter an RCU read-side critical section.
273 * The first cmm_barrier() call ensures that the compiler does not reorder
274 * the body of _rcu_read_lock() with a mutex.
276 * This function and its helper are both less than 10 lines long. The
277 * intent is that this function meets the 10-line criterion in LGPL,
278 * allowing this function to be invoked directly from non-LGPL code.
280 static inline void _rcu_read_lock(void)
285 tmp
= URCU_TLS(rcu_reader
).ctr
;
286 _rcu_read_lock_update(tmp
);
290 * This is a helper function for _rcu_read_unlock().
292 * The first smp_mb_slave() call ensures that the critical section is
293 * seen to precede the store to rcu_reader.ctr.
294 * The second smp_mb_slave() call ensures that we write to rcu_reader.ctr
295 * before reading the update-side futex.
297 static inline void _rcu_read_unlock_update_and_wakeup(unsigned long tmp
)
299 if (caa_likely((tmp
& RCU_GP_CTR_NEST_MASK
) == RCU_GP_COUNT
)) {
300 smp_mb_slave(RCU_MB_GROUP
);
301 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
).ctr
, URCU_TLS(rcu_reader
).ctr
- RCU_GP_COUNT
);
302 smp_mb_slave(RCU_MB_GROUP
);
305 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
).ctr
, URCU_TLS(rcu_reader
).ctr
- RCU_GP_COUNT
);
309 * Exit an RCU read-side crtical section. Both this function and its
310 * helper are smaller than 10 lines of code, and are intended to be
311 * usable by non-LGPL code, as called out in LGPL.
313 static inline void _rcu_read_unlock(void)
317 tmp
= URCU_TLS(rcu_reader
).ctr
;
318 _rcu_read_unlock_update_and_wakeup(tmp
);
319 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
326 #endif /* _URCU_STATIC_H */
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