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.
41 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
43 #define _LOAD_SHARED(p) ACCESS_ONCE(p)
46 * Load a data from shared memory, doing a cache flush if required.
48 #define LOAD_SHARED(p) \
55 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
57 #define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
60 * Store v into x, where x is located in shared memory. Performs the required
61 * cache flush after writing. Returns v.
63 #define STORE_SHARED(x, v) \
65 _STORE_SHARED(x, v); \
71 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
72 * into a RCU read-side critical section. The pointer can later be safely
73 * dereferenced within the critical section.
75 * This ensures that the pointer copy is invariant thorough the whole critical
78 * Inserts memory barriers on architectures that require them (currently only
79 * Alpha) and documents which pointers are protected by RCU.
81 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
84 #define _rcu_dereference(p) ({ \
85 typeof(p) _________p1 = LOAD_SHARED(p); \
86 smp_read_barrier_depends(); \
91 * This code section can only be included in LGPL 2.1 compatible source code.
92 * See below for the function call wrappers which can be used in code meant to
93 * be only linked with the Userspace RCU library. This comes with a small
94 * performance degradation on the read-side due to the added function calls.
95 * This is required to permit relinking with newer versions of the library.
99 * If a reader is really non-cooperative and refuses to commit its
100 * rcu_reader_qs_gp count to memory (there is no barrier in the reader
101 * per-se), kick it after a few loops waiting for it.
103 #define KICK_READER_LOOPS 10000
106 #define rcu_assert(args...) assert(args)
108 #define rcu_assert(args...)
117 #define YIELD_READ (1 << 0)
118 #define YIELD_WRITE (1 << 1)
120 /* maximum sleep delay, in us */
123 extern unsigned int yield_active
;
124 extern unsigned int __thread rand_yield
;
126 static inline void debug_yield_read(void)
128 if (yield_active
& YIELD_READ
)
129 if (rand_r(&rand_yield
) & 0x1)
130 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
133 static inline void debug_yield_write(void)
135 if (yield_active
& YIELD_WRITE
)
136 if (rand_r(&rand_yield
) & 0x1)
137 usleep(rand_r(&rand_yield
) % MAX_SLEEP
);
140 static inline void debug_yield_init(void)
142 rand_yield
= time(NULL
) ^ pthread_self();
145 static inline void debug_yield_read(void)
149 static inline void debug_yield_write(void)
153 static inline void debug_yield_init(void)
159 static inline void reader_barrier()
164 #define RCU_GP_ONLINE (1UL << 0)
165 #define RCU_GP_CTR (1UL << 1)
168 * Global quiescent period counter with low-order bits unused.
169 * Using a int rather than a char to eliminate false register dependencies
170 * causing stalls on some architectures.
172 extern unsigned long urcu_gp_ctr
;
174 extern unsigned long __thread rcu_reader_qs_gp
;
176 #if (BITS_PER_LONG < 64)
177 static inline int rcu_gp_ongoing(unsigned long *value
)
179 unsigned long reader_gp
;
183 reader_gp
= LOAD_SHARED(*value
);
184 return reader_gp
&& ((reader_gp
^ urcu_gp_ctr
) & RCU_GP_CTR
);
186 #else /* !(BITS_PER_LONG < 64) */
187 static inline int rcu_gp_ongoing(unsigned long *value
)
189 unsigned long reader_gp
;
193 reader_gp
= LOAD_SHARED(*value
);
194 return reader_gp
&& (reader_gp
- urcu_gp_ctr
> ULONG_MAX
/ 2);
196 #endif /* !(BITS_PER_LONG < 64) */
198 static inline void _rcu_read_lock(void)
200 rcu_assert(rcu_reader_qs_gp
);
203 static inline void _rcu_read_unlock(void)
207 static inline void _rcu_quiescent_state(void)
210 _STORE_SHARED(rcu_reader_qs_gp
, _LOAD_SHARED(urcu_gp_ctr
));
214 static inline void _rcu_thread_offline(void)
217 STORE_SHARED(rcu_reader_qs_gp
, 0);
220 static inline void _rcu_thread_online(void)
222 _STORE_SHARED(rcu_reader_qs_gp
, LOAD_SHARED(urcu_gp_ctr
));
227 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
228 * meant to be read by RCU read-side critical sections. Returns the assigned
231 * Documents which pointers will be dereferenced by RCU read-side critical
232 * sections and adds the required memory barriers on architectures requiring
233 * them. It also makes sure the compiler does not reorder code initializing the
234 * data structure before its publication.
236 * Should match rcu_dereference_pointer().
239 #define _rcu_assign_pointer(p, v) \
241 if (!__builtin_constant_p(v) || \
244 STORE_SHARED(p, v); \
248 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
249 * pointer to the data structure, which can be safely freed after waiting for a
250 * quiescent state using synchronize_rcu().
253 #define _rcu_xchg_pointer(p, v) \
255 if (!__builtin_constant_p(v) || \
262 * Exchanges the pointer and waits for quiescent state.
263 * The pointer returned can be freed.
265 #define _rcu_publish_content(p, v) \
268 oldptr = _rcu_xchg_pointer(p, v); \
273 #endif /* _URCU_QSBR_STATIC_H */