add rcu_cmpxchg_pointer
[urcu.git] / urcu-qsbr-static.h
1 #ifndef _URCU_QSBR_STATIC_H
2 #define _URCU_QSBR_STATIC_H
3
4 /*
5 * urcu-qsbr-static.h
6 *
7 * Userspace RCU QSBR header.
8 *
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-qsbr.h for linking
10 * dynamically with the userspace rcu QSBR 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 <assert.h>
35 #include <limits.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 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
82 */
83
84 #define _rcu_dereference(p) ({ \
85 typeof(p) _________p1 = LOAD_SHARED(p); \
86 smp_read_barrier_depends(); \
87 (_________p1); \
88 })
89
90 /*
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.
96 */
97
98 /*
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.
102 */
103 #define KICK_READER_LOOPS 10000
104
105 #ifdef DEBUG_RCU
106 #define rcu_assert(args...) assert(args)
107 #else
108 #define rcu_assert(args...)
109 #endif
110
111 #ifdef DEBUG_YIELD
112 #include <sched.h>
113 #include <time.h>
114 #include <pthread.h>
115 #include <unistd.h>
116
117 #define YIELD_READ (1 << 0)
118 #define YIELD_WRITE (1 << 1)
119
120 /* maximum sleep delay, in us */
121 #define MAX_SLEEP 50
122
123 extern unsigned int yield_active;
124 extern unsigned int __thread rand_yield;
125
126 static inline void debug_yield_read(void)
127 {
128 if (yield_active & YIELD_READ)
129 if (rand_r(&rand_yield) & 0x1)
130 usleep(rand_r(&rand_yield) % MAX_SLEEP);
131 }
132
133 static inline void debug_yield_write(void)
134 {
135 if (yield_active & YIELD_WRITE)
136 if (rand_r(&rand_yield) & 0x1)
137 usleep(rand_r(&rand_yield) % MAX_SLEEP);
138 }
139
140 static inline void debug_yield_init(void)
141 {
142 rand_yield = time(NULL) ^ pthread_self();
143 }
144 #else
145 static inline void debug_yield_read(void)
146 {
147 }
148
149 static inline void debug_yield_write(void)
150 {
151 }
152
153 static inline void debug_yield_init(void)
154 {
155
156 }
157 #endif
158
159 static inline void reader_barrier()
160 {
161 smp_mb();
162 }
163
164 #define RCU_GP_ONLINE (1UL << 0)
165 #define RCU_GP_CTR (1UL << 1)
166
167 /*
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.
171 */
172 extern unsigned long urcu_gp_ctr;
173
174 extern unsigned long __thread rcu_reader_qs_gp;
175
176 #if (BITS_PER_LONG < 64)
177 static inline int rcu_gp_ongoing(unsigned long *value)
178 {
179 unsigned long reader_gp;
180
181 if (value == NULL)
182 return 0;
183 reader_gp = LOAD_SHARED(*value);
184 return reader_gp && ((reader_gp ^ urcu_gp_ctr) & RCU_GP_CTR);
185 }
186 #else /* !(BITS_PER_LONG < 64) */
187 static inline int rcu_gp_ongoing(unsigned long *value)
188 {
189 unsigned long reader_gp;
190
191 if (value == NULL)
192 return 0;
193 reader_gp = LOAD_SHARED(*value);
194 return reader_gp && (reader_gp - urcu_gp_ctr > ULONG_MAX / 2);
195 }
196 #endif /* !(BITS_PER_LONG < 64) */
197
198 static inline void _rcu_read_lock(void)
199 {
200 rcu_assert(rcu_reader_qs_gp);
201 }
202
203 static inline void _rcu_read_unlock(void)
204 {
205 }
206
207 static inline void _rcu_quiescent_state(void)
208 {
209 smp_mb();
210 _STORE_SHARED(rcu_reader_qs_gp, _LOAD_SHARED(urcu_gp_ctr));
211 smp_mb();
212 }
213
214 static inline void _rcu_thread_offline(void)
215 {
216 smp_mb();
217 STORE_SHARED(rcu_reader_qs_gp, 0);
218 }
219
220 static inline void _rcu_thread_online(void)
221 {
222 _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
223 smp_mb();
224 }
225
226 /**
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
229 * value.
230 *
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.
235 *
236 * Should match rcu_dereference_pointer().
237 */
238
239 #define _rcu_assign_pointer(p, v) \
240 ({ \
241 if (!__builtin_constant_p(v) || \
242 ((v) != NULL)) \
243 wmb(); \
244 STORE_SHARED(p, v); \
245 })
246
247 /**
248 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
249 * is as expected by "old". If succeeds, returns the previous pointer to the
250 * data structure, which can be safely freed after waiting for a quiescent state
251 * using synchronize_rcu(). If fails (unexpected value), returns old (which
252 * should not be freed !).
253 */
254
255 #define _rcu_cmpxchg_pointer(p, old, _new) \
256 ({ \
257 if (!__builtin_constant_p(_new) || \
258 ((_new) != NULL)) \
259 wmb(); \
260 cmpxchg(p, old, _new); \
261 })
262
263 /**
264 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
265 * pointer to the data structure, which can be safely freed after waiting for a
266 * quiescent state using synchronize_rcu().
267 */
268
269 #define _rcu_xchg_pointer(p, v) \
270 ({ \
271 if (!__builtin_constant_p(v) || \
272 ((v) != NULL)) \
273 wmb(); \
274 xchg(p, v); \
275 })
276
277 /*
278 * Exchanges the pointer and waits for quiescent state.
279 * The pointer returned can be freed.
280 */
281 #define _rcu_publish_content(p, v) \
282 ({ \
283 void *oldptr; \
284 oldptr = _rcu_xchg_pointer(p, v); \
285 synchronize_rcu(); \
286 oldptr; \
287 })
288
289 #endif /* _URCU_QSBR_STATIC_H */
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