1 #ifndef _URCU_QSBR_STATIC_H
2 #define _URCU_QSBR_STATIC_H
7 * Userspace RCU QSBR header.
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-qsbr.h for linking
10 * dynamically with the userspace rcu QSBR 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.
43 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
45 #define _LOAD_SHARED(p) ACCESS_ONCE(p)
48 * Load a data from shared memory, doing a cache flush if required.
50 #define LOAD_SHARED(p) \
57 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
59 #define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
62 * Store v into x, where x is located in shared memory. Performs the required
63 * cache flush after writing. Returns v.
65 #define STORE_SHARED(x, v) \
67 _STORE_SHARED(x, v); \
73 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
74 * into a RCU read-side critical section. The pointer can later be safely
75 * dereferenced within the critical section.
77 * This ensures that the pointer copy is invariant thorough the whole critical
80 * Inserts memory barriers on architectures that require them (currently only
81 * Alpha) and documents which pointers are protected by RCU.
83 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
86 #define _rcu_dereference(p) ({ \
87 typeof(p) _________p1 = LOAD_SHARED(p); \
88 smp_read_barrier_depends(); \
92 #define futex(...) syscall(__NR_futex, __VA_ARGS__)
97 * This code section can only be included in LGPL 2.1 compatible source code.
98 * See below for the function call wrappers which can be used in code meant to
99 * be only linked with the Userspace RCU library. This comes with a small
100 * performance degradation on the read-side due to the added function calls.
101 * This is required to permit relinking with newer versions of the library.
105 * If a reader is really non-cooperative and refuses to commit its
106 * rcu_reader_qs_gp count to memory (there is no barrier in the reader
107 * per-se), kick it after a few loops waiting for it.
109 #define KICK_READER_LOOPS 10000
112 * Active attempts to check for reader Q.S. before calling futex().
114 #define RCU_QS_ACTIVE_ATTEMPTS 100
117 #define rcu_assert(args...) assert(args)
119 #define rcu_assert(args...)
128 #define YIELD_READ (1 << 0)
129 #define YIELD_WRITE (1 << 1)
131 /* maximum sleep delay, in us */
134 extern unsigned int yield_active
;
135 extern unsigned int __thread rand_yield
;
137 static inline void debug_yield_read(void)
139 if (yield_active
& YIELD_READ
)
140 if (rand_r(&rand_yield
) & 0x1)
141 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
144 static inline void debug_yield_write(void)
146 if (yield_active
& YIELD_WRITE
)
147 if (rand_r(&rand_yield
) & 0x1)
148 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
151 static inline void debug_yield_init(void)
153 rand_yield
= time(NULL
) ^ pthread_self();
156 static inline void debug_yield_read(void)
160 static inline void debug_yield_write(void)
164 static inline void debug_yield_init(void)
170 static inline void reader_barrier()
175 #define RCU_GP_ONLINE (1UL << 0)
176 #define RCU_GP_CTR (1UL << 1)
179 * Global quiescent period counter with low-order bits unused.
180 * Using a int rather than a char to eliminate false register dependencies
181 * causing stalls on some architectures.
183 extern unsigned long urcu_gp_ctr
;
185 extern unsigned long __thread rcu_reader_qs_gp
;
190 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
192 static inline void wake_up_gp(void)
194 if (unlikely(atomic_read(&gp_futex
) == -1)) {
195 atomic_set(&gp_futex
, 0);
196 futex(&gp_futex
, FUTEX_WAKE
, 1,
201 #if (BITS_PER_LONG < 64)
202 static inline int rcu_gp_ongoing(unsigned long *value
)
204 unsigned long reader_gp
;
208 reader_gp
= LOAD_SHARED(*value
);
209 return reader_gp
&& ((reader_gp
^ urcu_gp_ctr
) & RCU_GP_CTR
);
211 #else /* !(BITS_PER_LONG < 64) */
212 static inline int rcu_gp_ongoing(unsigned long *value
)
214 unsigned long reader_gp
;
218 reader_gp
= LOAD_SHARED(*value
);
219 return reader_gp
&& (reader_gp
- urcu_gp_ctr
> ULONG_MAX
/ 2);
221 #endif /* !(BITS_PER_LONG < 64) */
223 static inline void _rcu_read_lock(void)
225 rcu_assert(rcu_reader_qs_gp
);
228 static inline void _rcu_read_unlock(void)
232 static inline void _rcu_quiescent_state(void)
235 _STORE_SHARED(rcu_reader_qs_gp
, _LOAD_SHARED(urcu_gp_ctr
));
236 smp_mb(); /* write rcu_reader_qs_gp before read futex */
241 static inline void _rcu_thread_offline(void)
244 STORE_SHARED(rcu_reader_qs_gp
, 0);
245 smp_mb(); /* write rcu_reader_qs_gp before read futex */
249 static inline void _rcu_thread_online(void)
251 _STORE_SHARED(rcu_reader_qs_gp
, LOAD_SHARED(urcu_gp_ctr
));
256 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
257 * meant to be read by RCU read-side critical sections. Returns the assigned
260 * Documents which pointers will be dereferenced by RCU read-side critical
261 * sections and adds the required memory barriers on architectures requiring
262 * them. It also makes sure the compiler does not reorder code initializing the
263 * data structure before its publication.
265 * Should match rcu_dereference_pointer().
268 #define _rcu_assign_pointer(p, v) \
270 if (!__builtin_constant_p(v) || \
273 STORE_SHARED(p, v); \
277 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
278 * is as expected by "old". If succeeds, returns the previous pointer to the
279 * data structure, which can be safely freed after waiting for a quiescent state
280 * using synchronize_rcu(). If fails (unexpected value), returns old (which
281 * should not be freed !).
284 #define _rcu_cmpxchg_pointer(p, old, _new) \
286 if (!__builtin_constant_p(_new) || \
289 cmpxchg(p, old, _new); \
293 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
294 * pointer to the data structure, which can be safely freed after waiting for a
295 * quiescent state using synchronize_rcu().
298 #define _rcu_xchg_pointer(p, v) \
300 if (!__builtin_constant_p(v) || \
307 * Exchanges the pointer and waits for quiescent state.
308 * The pointer returned can be freed.
310 #define _rcu_publish_content(p, v) \
313 oldptr = _rcu_xchg_pointer(p, v); \
318 #endif /* _URCU_QSBR_STATIC_H */