add rcu_cmpxchg_pointer
[urcu.git] / urcu-static.h
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1#ifndef _URCU_STATIC_H
2#define _URCU_STATIC_H
3
4/*
5 * urcu-static.h
6 *
d2d23035 7 * Userspace RCU header.
adcfce54 8 *
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9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
10 * dynamically with the userspace rcu library.
adcfce54 11 *
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12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
adcfce54 14 *
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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
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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
35#include <compiler.h>
36#include <arch.h>
37
38/*
39 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
40 */
41#define _LOAD_SHARED(p) ACCESS_ONCE(p)
42
43/*
44 * Load a data from shared memory, doing a cache flush if required.
45 */
46#define LOAD_SHARED(p) \
47 ({ \
48 smp_rmc(); \
49 _LOAD_SHARED(p); \
50 })
51
52/*
53 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
54 */
55#define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
56
57/*
58 * Store v into x, where x is located in shared memory. Performs the required
59 * cache flush after writing. Returns v.
60 */
61#define STORE_SHARED(x, v) \
62 ({ \
63 _STORE_SHARED(x, v); \
64 smp_wmc(); \
65 (v); \
66 })
67
68/**
69 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
70 * into a RCU read-side critical section. The pointer can later be safely
71 * dereferenced within the critical section.
72 *
73 * This ensures that the pointer copy is invariant thorough the whole critical
74 * section.
75 *
76 * Inserts memory barriers on architectures that require them (currently only
77 * Alpha) and documents which pointers are protected by RCU.
78 *
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79 * The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
80 * optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
81 * data read before the pointer read by speculating the value of the pointer.
82 * Correct ordering is ensured because the pointer is read as a volatile access.
83 * This acts as a global side-effect operation, which forbids reordering of
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84 * dependent memory operations. Note that such concern about dependency-breaking
85 * optimizations will eventually be taken care of by the "memory_order_consume"
86 * addition to forthcoming C++ standard.
809f4fde 87 *
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88 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
89 */
90
91#define _rcu_dereference(p) ({ \
92 typeof(p) _________p1 = LOAD_SHARED(p); \
93 smp_read_barrier_depends(); \
94 (_________p1); \
95 })
96
97/*
98 * This code section can only be included in LGPL 2.1 compatible source code.
99 * See below for the function call wrappers which can be used in code meant to
100 * be only linked with the Userspace RCU library. This comes with a small
101 * performance degradation on the read-side due to the added function calls.
102 * This is required to permit relinking with newer versions of the library.
103 */
104
105/*
106 * The signal number used by the RCU library can be overridden with
107 * -DSIGURCU= when compiling the library.
108 */
109#ifndef SIGURCU
110#define SIGURCU SIGUSR1
111#endif
112
113/*
114 * If a reader is really non-cooperative and refuses to commit its
115 * urcu_active_readers count to memory (there is no barrier in the reader
116 * per-se), kick it after a few loops waiting for it.
117 */
118#define KICK_READER_LOOPS 10000
119
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120#ifdef DEBUG_RCU
121#define rcu_assert(args...) assert(args)
122#else
123#define rcu_assert(args...)
124#endif
125
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126#ifdef DEBUG_YIELD
127#include <sched.h>
128#include <time.h>
129#include <pthread.h>
130#include <unistd.h>
131
132#define YIELD_READ (1 << 0)
133#define YIELD_WRITE (1 << 1)
134
b4ce1526 135/*
0a1d290b 136 * Updates without URCU_MB are much slower. Account this in
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137 * the delay.
138 */
0a1d290b 139#ifdef URCU_MB
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140/* maximum sleep delay, in us */
141#define MAX_SLEEP 50
142#else
143#define MAX_SLEEP 30000
144#endif
145
146extern unsigned int yield_active;
147extern unsigned int __thread rand_yield;
148
149static inline void debug_yield_read(void)
150{
151 if (yield_active & YIELD_READ)
152 if (rand_r(&rand_yield) & 0x1)
153 usleep(rand_r(&rand_yield) % MAX_SLEEP);
154}
155
156static inline void debug_yield_write(void)
157{
158 if (yield_active & YIELD_WRITE)
159 if (rand_r(&rand_yield) & 0x1)
160 usleep(rand_r(&rand_yield) % MAX_SLEEP);
161}
162
163static inline void debug_yield_init(void)
164{
165 rand_yield = time(NULL) ^ pthread_self();
166}
167#else
168static inline void debug_yield_read(void)
169{
170}
171
172static inline void debug_yield_write(void)
173{
174}
175
176static inline void debug_yield_init(void)
177{
178
179}
180#endif
181
0a1d290b 182#ifdef URCU_MB
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183static inline void reader_barrier()
184{
185 smp_mb();
186}
187#else
188static inline void reader_barrier()
189{
190 barrier();
191}
192#endif
193
194/*
195 * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
196 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
197 */
198#define RCU_GP_COUNT (1UL << 0)
199/* Use the amount of bits equal to half of the architecture long size */
200#define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
201#define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
202
203/*
204 * Global quiescent period counter with low-order bits unused.
205 * Using a int rather than a char to eliminate false register dependencies
206 * causing stalls on some architectures.
207 */
208extern long urcu_gp_ctr;
209
210extern long __thread urcu_active_readers;
211
212static inline int rcu_old_gp_ongoing(long *value)
213{
214 long v;
215
216 if (value == NULL)
217 return 0;
218 /*
219 * Make sure both tests below are done on the same version of *value
220 * to insure consistency.
221 */
222 v = LOAD_SHARED(*value);
223 return (v & RCU_GP_CTR_NEST_MASK) &&
224 ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
225}
226
227static inline void _rcu_read_lock(void)
228{
229 long tmp;
230
231 tmp = urcu_active_readers;
232 /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
67ef1a2c 233 if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
adcfce54 234 _STORE_SHARED(urcu_active_readers, _LOAD_SHARED(urcu_gp_ctr));
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235 /*
236 * Set active readers count for outermost nesting level before
237 * accessing the pointer. See force_mb_all_threads().
238 */
239 reader_barrier();
240 } else {
adcfce54 241 _STORE_SHARED(urcu_active_readers, tmp + RCU_GP_COUNT);
67ef1a2c 242 }
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243}
244
245static inline void _rcu_read_unlock(void)
246{
247 reader_barrier();
248 /*
249 * Finish using rcu before decrementing the pointer.
250 * See force_mb_all_threads().
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251 * Formally only needed for outermost nesting level, but leave barrier
252 * in place for nested unlocks to remove a branch from the common case
253 * (no nesting).
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254 */
255 _STORE_SHARED(urcu_active_readers, urcu_active_readers - RCU_GP_COUNT);
256}
257
258/**
259 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
260 * meant to be read by RCU read-side critical sections. Returns the assigned
261 * value.
262 *
263 * Documents which pointers will be dereferenced by RCU read-side critical
264 * sections and adds the required memory barriers on architectures requiring
265 * them. It also makes sure the compiler does not reorder code initializing the
266 * data structure before its publication.
267 *
268 * Should match rcu_dereference_pointer().
269 */
270
271#define _rcu_assign_pointer(p, v) \
272 ({ \
273 if (!__builtin_constant_p(v) || \
274 ((v) != NULL)) \
275 wmb(); \
276 STORE_SHARED(p, v); \
277 })
278
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279/**
280 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
281 * is as expected by "old". If succeeds, returns the previous pointer to the
282 * data structure, which can be safely freed after waiting for a quiescent state
283 * using synchronize_rcu(). If fails (unexpected value), returns old (which
284 * should not be freed !).
285 */
286
287#define _rcu_cmpxchg_pointer(p, old, _new) \
288 ({ \
289 if (!__builtin_constant_p(_new) || \
290 ((_new) != NULL)) \
291 wmb(); \
292 cmpxchg(p, old, _new); \
293 })
294
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295/**
296 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
67ef1a2c 297 * pointer to the data structure, which can be safely freed after waiting for a
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298 * quiescent state using synchronize_rcu().
299 */
300
301#define _rcu_xchg_pointer(p, v) \
302 ({ \
303 if (!__builtin_constant_p(v) || \
304 ((v) != NULL)) \
305 wmb(); \
306 xchg(p, v); \
307 })
308
309/*
310 * Exchanges the pointer and waits for quiescent state.
311 * The pointer returned can be freed.
312 */
313#define _rcu_publish_content(p, v) \
314 ({ \
315 void *oldptr; \
316 oldptr = _rcu_xchg_pointer(p, v); \
317 synchronize_rcu(); \
318 oldptr; \
319 })
320
321#endif /* _URCU_STATIC_H */
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