Add missing rcu_cmpxchg_pointer define
[urcu.git] / urcu-static.h
1 #ifndef _URCU_STATIC_H
2 #define _URCU_STATIC_H
3
4 /*
5 * urcu-static.h
6 *
7 * Userspace RCU header.
8 *
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
10 * dynamically with the userspace rcu library.
11 *
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
14 *
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.
19 *
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.
24 *
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
28 *
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
30 */
31
32 #include <stdlib.h>
33 #include <pthread.h>
34 #include <syscall.h>
35 #include <unistd.h>
36
37 #include <compiler.h>
38 #include <arch.h>
39
40 /*
41 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
42 */
43 #define _LOAD_SHARED(p) ACCESS_ONCE(p)
44
45 /*
46 * Load a data from shared memory, doing a cache flush if required.
47 */
48 #define LOAD_SHARED(p) \
49 ({ \
50 smp_rmc(); \
51 _LOAD_SHARED(p); \
52 })
53
54 /*
55 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
56 */
57 #define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
58
59 /*
60 * Store v into x, where x is located in shared memory. Performs the required
61 * cache flush after writing. Returns v.
62 */
63 #define STORE_SHARED(x, v) \
64 ({ \
65 _STORE_SHARED(x, v); \
66 smp_wmc(); \
67 (v); \
68 })
69
70 /**
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.
74 *
75 * This ensures that the pointer copy is invariant thorough the whole critical
76 * section.
77 *
78 * Inserts memory barriers on architectures that require them (currently only
79 * Alpha) and documents which pointers are protected by RCU.
80 *
81 * The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
82 * optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
83 * data read before the pointer read by speculating the value of the pointer.
84 * Correct ordering is ensured because the pointer is read as a volatile access.
85 * This acts as a global side-effect operation, which forbids reordering of
86 * dependent memory operations. Note that such concern about dependency-breaking
87 * optimizations will eventually be taken care of by the "memory_order_consume"
88 * addition to forthcoming C++ standard.
89 *
90 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
91 */
92
93 #define _rcu_dereference(p) ({ \
94 typeof(p) _________p1 = LOAD_SHARED(p); \
95 smp_read_barrier_depends(); \
96 (_________p1); \
97 })
98
99 #define futex(...) syscall(__NR_futex, __VA_ARGS__)
100 #define FUTEX_WAIT 0
101 #define FUTEX_WAKE 1
102
103 /*
104 * This code section can only be included in LGPL 2.1 compatible source code.
105 * See below for the function call wrappers which can be used in code meant to
106 * be only linked with the Userspace RCU library. This comes with a small
107 * performance degradation on the read-side due to the added function calls.
108 * This is required to permit relinking with newer versions of the library.
109 */
110
111 /*
112 * The signal number used by the RCU library can be overridden with
113 * -DSIGURCU= when compiling the library.
114 */
115 #ifndef SIGURCU
116 #define SIGURCU SIGUSR1
117 #endif
118
119 /*
120 * If a reader is really non-cooperative and refuses to commit its
121 * urcu_active_readers count to memory (there is no barrier in the reader
122 * per-se), kick it after a few loops waiting for it.
123 */
124 #define KICK_READER_LOOPS 10000
125
126 /*
127 * Active attempts to check for reader Q.S. before calling futex().
128 */
129 #define RCU_QS_ACTIVE_ATTEMPTS 100
130
131 #ifdef DEBUG_RCU
132 #define rcu_assert(args...) assert(args)
133 #else
134 #define rcu_assert(args...)
135 #endif
136
137 #ifdef DEBUG_YIELD
138 #include <sched.h>
139 #include <time.h>
140 #include <pthread.h>
141 #include <unistd.h>
142
143 #define YIELD_READ (1 << 0)
144 #define YIELD_WRITE (1 << 1)
145
146 /*
147 * Updates without URCU_MB are much slower. Account this in
148 * the delay.
149 */
150 #ifdef URCU_MB
151 /* maximum sleep delay, in us */
152 #define MAX_SLEEP 50
153 #else
154 #define MAX_SLEEP 30000
155 #endif
156
157 extern unsigned int yield_active;
158 extern unsigned int __thread rand_yield;
159
160 static inline void debug_yield_read(void)
161 {
162 if (yield_active & YIELD_READ)
163 if (rand_r(&rand_yield) & 0x1)
164 usleep(rand_r(&rand_yield) % MAX_SLEEP);
165 }
166
167 static inline void debug_yield_write(void)
168 {
169 if (yield_active & YIELD_WRITE)
170 if (rand_r(&rand_yield) & 0x1)
171 usleep(rand_r(&rand_yield) % MAX_SLEEP);
172 }
173
174 static inline void debug_yield_init(void)
175 {
176 rand_yield = time(NULL) ^ pthread_self();
177 }
178 #else
179 static inline void debug_yield_read(void)
180 {
181 }
182
183 static inline void debug_yield_write(void)
184 {
185 }
186
187 static inline void debug_yield_init(void)
188 {
189
190 }
191 #endif
192
193 #ifdef URCU_MB
194 static inline void reader_barrier()
195 {
196 smp_mb();
197 }
198 #else
199 static inline void reader_barrier()
200 {
201 barrier();
202 }
203 #endif
204
205 /*
206 * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
207 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
208 */
209 #define RCU_GP_COUNT (1UL << 0)
210 /* Use the amount of bits equal to half of the architecture long size */
211 #define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
212 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
213
214 /*
215 * Global quiescent period counter with low-order bits unused.
216 * Using a int rather than a char to eliminate false register dependencies
217 * causing stalls on some architectures.
218 */
219 extern long urcu_gp_ctr;
220
221 extern long __thread urcu_active_readers;
222
223 extern int gp_futex;
224
225 /*
226 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
227 */
228 static inline void wake_up_gp(void)
229 {
230 if (unlikely(atomic_read(&gp_futex) == -1)) {
231 atomic_set(&gp_futex, 0);
232 futex(&gp_futex, FUTEX_WAKE, 1,
233 NULL, NULL, 0);
234 }
235 }
236
237 static inline int rcu_old_gp_ongoing(long *value)
238 {
239 long v;
240
241 if (value == NULL)
242 return 0;
243 /*
244 * Make sure both tests below are done on the same version of *value
245 * to insure consistency.
246 */
247 v = LOAD_SHARED(*value);
248 return (v & RCU_GP_CTR_NEST_MASK) &&
249 ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
250 }
251
252 static inline void _rcu_read_lock(void)
253 {
254 long tmp;
255
256 tmp = urcu_active_readers;
257 /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
258 if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
259 _STORE_SHARED(urcu_active_readers, _LOAD_SHARED(urcu_gp_ctr));
260 /*
261 * Set active readers count for outermost nesting level before
262 * accessing the pointer. See force_mb_all_threads().
263 */
264 reader_barrier();
265 } else {
266 _STORE_SHARED(urcu_active_readers, tmp + RCU_GP_COUNT);
267 }
268 }
269
270 static inline void _rcu_read_unlock(void)
271 {
272 long tmp;
273
274 tmp = urcu_active_readers;
275 /*
276 * Finish using rcu before decrementing the pointer.
277 * See force_mb_all_threads().
278 */
279 if (likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
280 reader_barrier();
281 _STORE_SHARED(urcu_active_readers,
282 urcu_active_readers - RCU_GP_COUNT);
283 /* write urcu_active_readers before read futex */
284 reader_barrier();
285 wake_up_gp();
286 } else {
287 _STORE_SHARED(urcu_active_readers,
288 urcu_active_readers - RCU_GP_COUNT);
289 }
290 }
291
292 /**
293 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
294 * meant to be read by RCU read-side critical sections. Returns the assigned
295 * value.
296 *
297 * Documents which pointers will be dereferenced by RCU read-side critical
298 * sections and adds the required memory barriers on architectures requiring
299 * them. It also makes sure the compiler does not reorder code initializing the
300 * data structure before its publication.
301 *
302 * Should match rcu_dereference_pointer().
303 */
304
305 #define _rcu_assign_pointer(p, v) \
306 ({ \
307 if (!__builtin_constant_p(v) || \
308 ((v) != NULL)) \
309 wmb(); \
310 STORE_SHARED(p, v); \
311 })
312
313 /**
314 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
315 * is as expected by "old". If succeeds, returns the previous pointer to the
316 * data structure, which can be safely freed after waiting for a quiescent state
317 * using synchronize_rcu(). If fails (unexpected value), returns old (which
318 * should not be freed !).
319 */
320
321 #define _rcu_cmpxchg_pointer(p, old, _new) \
322 ({ \
323 if (!__builtin_constant_p(_new) || \
324 ((_new) != NULL)) \
325 wmb(); \
326 cmpxchg(p, old, _new); \
327 })
328
329 /**
330 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
331 * pointer to the data structure, which can be safely freed after waiting for a
332 * quiescent state using synchronize_rcu().
333 */
334
335 #define _rcu_xchg_pointer(p, v) \
336 ({ \
337 if (!__builtin_constant_p(v) || \
338 ((v) != NULL)) \
339 wmb(); \
340 xchg(p, v); \
341 })
342
343 /*
344 * Exchanges the pointer and waits for quiescent state.
345 * The pointer returned can be freed.
346 */
347 #define _rcu_publish_content(p, v) \
348 ({ \
349 void *oldptr; \
350 oldptr = _rcu_xchg_pointer(p, v); \
351 synchronize_rcu(); \
352 oldptr; \
353 })
354
355 #endif /* _URCU_STATIC_H */
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