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.
40 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
42 #define _LOAD_SHARED(p) ACCESS_ONCE(p)
45 * Load a data from shared memory, doing a cache flush if required.
47 #define LOAD_SHARED(p) \
54 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
56 #define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
59 * Store v into x, where x is located in shared memory. Performs the required
60 * cache flush after writing. Returns v.
62 #define STORE_SHARED(x, v) \
64 _STORE_SHARED(x, v); \
70 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
71 * into a RCU read-side critical section. The pointer can later be safely
72 * dereferenced within the critical section.
74 * This ensures that the pointer copy is invariant thorough the whole critical
77 * Inserts memory barriers on architectures that require them (currently only
78 * Alpha) and documents which pointers are protected by RCU.
80 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
83 #define _rcu_dereference(p) ({ \
84 typeof(p) _________p1 = LOAD_SHARED(p); \
85 smp_read_barrier_depends(); \
90 * This code section can only be included in LGPL 2.1 compatible source code.
91 * See below for the function call wrappers which can be used in code meant to
92 * be only linked with the Userspace RCU library. This comes with a small
93 * performance degradation on the read-side due to the added function calls.
94 * This is required to permit relinking with newer versions of the library.
98 * The signal number used by the RCU library can be overridden with
99 * -DSIGURCU= when compiling the library.
102 #define SIGURCU SIGUSR1
106 * If a reader is really non-cooperative and refuses to commit its
107 * rcu_reader_qs_gp count to memory (there is no barrier in the reader
108 * per-se), kick it after a few loops waiting for it.
110 #define KICK_READER_LOOPS 10000
113 #define rcu_assert(args...) assert(args)
115 #define rcu_assert(args...)
124 #define YIELD_READ (1 << 0)
125 #define YIELD_WRITE (1 << 1)
127 /* maximum sleep delay, in us */
130 extern unsigned int yield_active
;
131 extern unsigned int __thread rand_yield
;
133 static inline void debug_yield_read(void)
135 if (yield_active
& YIELD_READ
)
136 if (rand_r(&rand_yield
) & 0x1)
137 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
140 static inline void debug_yield_write(void)
142 if (yield_active
& YIELD_WRITE
)
143 if (rand_r(&rand_yield
) & 0x1)
144 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
147 static inline void debug_yield_init(void)
149 rand_yield
= time(NULL
) ^ pthread_self();
152 static inline void debug_yield_read(void)
156 static inline void debug_yield_write(void)
160 static inline void debug_yield_init(void)
166 static inline void reader_barrier()
172 * Global quiescent period counter with low-order bits unused.
173 * Using a int rather than a char to eliminate false register dependencies
174 * causing stalls on some architectures.
176 extern long urcu_gp_ctr
;
178 extern long __thread rcu_reader_qs_gp
;
180 static inline int rcu_gp_ongoing(long *value
)
185 return LOAD_SHARED(*value
) & 1;
188 static inline void _rcu_read_lock(void)
190 rcu_assert(rcu_reader_qs_gp
& 1);
193 static inline void _rcu_read_unlock(void)
197 static inline void _rcu_quiescent_state(void)
200 rcu_reader_qs_gp
= ACCESS_ONCE(urcu_gp_ctr
) + 1;
204 static inline void _rcu_thread_offline(void)
207 rcu_reader_qs_gp
= ACCESS_ONCE(urcu_gp_ctr
);
210 static inline void _rcu_thread_online(void)
212 rcu_reader_qs_gp
= ACCESS_ONCE(urcu_gp_ctr
) + 1;
217 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
218 * meant to be read by RCU read-side critical sections. Returns the assigned
221 * Documents which pointers will be dereferenced by RCU read-side critical
222 * sections and adds the required memory barriers on architectures requiring
223 * them. It also makes sure the compiler does not reorder code initializing the
224 * data structure before its publication.
226 * Should match rcu_dereference_pointer().
229 #define _rcu_assign_pointer(p, v) \
231 if (!__builtin_constant_p(v) || \
234 STORE_SHARED(p, v); \
238 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
239 * pointer to the data structure, which can be safely freed after waiting for a
240 * quiescent state using synchronize_rcu().
243 #define _rcu_xchg_pointer(p, v) \
245 if (!__builtin_constant_p(v) || \
252 * Exchanges the pointer and waits for quiescent state.
253 * The pointer returned can be freed.
255 #define _rcu_publish_content(p, v) \
258 oldptr = _rcu_xchg_pointer(p, v); \
263 extern void synchronize_rcu(void);
266 * Reader thread registration.
268 extern void rcu_register_thread(void);
269 extern void rcu_unregister_thread(void);
271 #endif /* _URCU_QSBR_H */