urcu (signal/mb): move thread checks outside lock
[urcu.git] / urcu-qsbr-static.h
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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>
f0f7dbdd 35#include <limits.h>
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36#include <syscall.h>
37#include <unistd.h>
7ac06cef 38
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39#include <urcu/compiler.h>
40#include <urcu/arch.h>
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41
42/*
43 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
44 */
45#define _LOAD_SHARED(p) ACCESS_ONCE(p)
46
47/*
48 * Load a data from shared memory, doing a cache flush if required.
49 */
50#define LOAD_SHARED(p) \
51 ({ \
52 smp_rmc(); \
53 _LOAD_SHARED(p); \
54 })
55
56/*
57 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
58 */
59#define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
60
61/*
62 * Store v into x, where x is located in shared memory. Performs the required
63 * cache flush after writing. Returns v.
64 */
65#define STORE_SHARED(x, v) \
66 ({ \
67 _STORE_SHARED(x, v); \
68 smp_wmc(); \
69 (v); \
70 })
71
72/**
73 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
74 * into a RCU read-side critical section. The pointer can later be safely
75 * dereferenced within the critical section.
76 *
77 * This ensures that the pointer copy is invariant thorough the whole critical
78 * section.
79 *
80 * Inserts memory barriers on architectures that require them (currently only
81 * Alpha) and documents which pointers are protected by RCU.
82 *
83 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
84 */
85
86#define _rcu_dereference(p) ({ \
87 typeof(p) _________p1 = LOAD_SHARED(p); \
88 smp_read_barrier_depends(); \
89 (_________p1); \
90 })
91
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92#define futex(...) syscall(__NR_futex, __VA_ARGS__)
93#define FUTEX_WAIT 0
94#define FUTEX_WAKE 1
95
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96/*
97 * This code section can only be included in LGPL 2.1 compatible source code.
98 * See below for the function call wrappers which can be used in code meant to
99 * be only linked with the Userspace RCU library. This comes with a small
100 * performance degradation on the read-side due to the added function calls.
101 * This is required to permit relinking with newer versions of the library.
102 */
103
104/*
105 * If a reader is really non-cooperative and refuses to commit its
106 * rcu_reader_qs_gp count to memory (there is no barrier in the reader
107 * per-se), kick it after a few loops waiting for it.
108 */
109#define KICK_READER_LOOPS 10000
110
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111/*
112 * Active attempts to check for reader Q.S. before calling futex().
113 */
114#define RCU_QS_ACTIVE_ATTEMPTS 100
115
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116#ifdef DEBUG_RCU
117#define rcu_assert(args...) assert(args)
118#else
119#define rcu_assert(args...)
120#endif
121
122#ifdef DEBUG_YIELD
123#include <sched.h>
124#include <time.h>
125#include <pthread.h>
126#include <unistd.h>
127
128#define YIELD_READ (1 << 0)
129#define YIELD_WRITE (1 << 1)
130
131/* maximum sleep delay, in us */
132#define MAX_SLEEP 50
133
134extern unsigned int yield_active;
135extern unsigned int __thread rand_yield;
136
137static inline void debug_yield_read(void)
138{
139 if (yield_active & YIELD_READ)
140 if (rand_r(&rand_yield) & 0x1)
141 usleep(rand_r(&rand_yield) % MAX_SLEEP);
142}
143
144static inline void debug_yield_write(void)
145{
146 if (yield_active & YIELD_WRITE)
147 if (rand_r(&rand_yield) & 0x1)
148 usleep(rand_r(&rand_yield) % MAX_SLEEP);
149}
150
151static inline void debug_yield_init(void)
152{
153 rand_yield = time(NULL) ^ pthread_self();
154}
155#else
156static inline void debug_yield_read(void)
157{
158}
159
160static inline void debug_yield_write(void)
161{
162}
163
164static inline void debug_yield_init(void)
165{
166
167}
168#endif
169
170static inline void reader_barrier()
171{
172 smp_mb();
173}
174
ac258107 175#define RCU_GP_ONLINE (1UL << 0)
55570466 176#define RCU_GP_CTR (1UL << 1)
ac258107 177
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178/*
179 * Global quiescent period counter with low-order bits unused.
180 * Using a int rather than a char to eliminate false register dependencies
181 * causing stalls on some architectures.
182 */
f0f7dbdd 183extern unsigned long urcu_gp_ctr;
7ac06cef 184
f0f7dbdd 185extern unsigned long __thread rcu_reader_qs_gp;
7ac06cef 186
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187extern int gp_futex;
188
189/*
190 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
191 */
192static inline void wake_up_gp(void)
193{
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194 if (unlikely(uatomic_read(&gp_futex) == -1)) {
195 uatomic_set(&gp_futex, 0);
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196 futex(&gp_futex, FUTEX_WAKE, 1,
197 NULL, NULL, 0);
198 }
199}
200
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201#if (BITS_PER_LONG < 64)
202static inline int rcu_gp_ongoing(unsigned long *value)
203{
204 unsigned long reader_gp;
205
206 if (value == NULL)
207 return 0;
208 reader_gp = LOAD_SHARED(*value);
209 return reader_gp && ((reader_gp ^ urcu_gp_ctr) & RCU_GP_CTR);
210}
211#else /* !(BITS_PER_LONG < 64) */
f0f7dbdd 212static inline int rcu_gp_ongoing(unsigned long *value)
7ac06cef 213{
f0f7dbdd 214 unsigned long reader_gp;
4e560c17 215
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216 if (value == NULL)
217 return 0;
4e560c17 218 reader_gp = LOAD_SHARED(*value);
f0f7dbdd 219 return reader_gp && (reader_gp - urcu_gp_ctr > ULONG_MAX / 2);
7ac06cef 220}
47d2f29e 221#endif /* !(BITS_PER_LONG < 64) */
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222
223static inline void _rcu_read_lock(void)
224{
ac258107 225 rcu_assert(rcu_reader_qs_gp);
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226}
227
228static inline void _rcu_read_unlock(void)
229{
230}
231
232static inline void _rcu_quiescent_state(void)
233{
234 smp_mb();
ab179a17 235 _STORE_SHARED(rcu_reader_qs_gp, _LOAD_SHARED(urcu_gp_ctr));
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236 smp_mb(); /* write rcu_reader_qs_gp before read futex */
237 wake_up_gp();
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238 smp_mb();
239}
240
241static inline void _rcu_thread_offline(void)
242{
243 smp_mb();
4e560c17 244 STORE_SHARED(rcu_reader_qs_gp, 0);
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245 smp_mb(); /* write rcu_reader_qs_gp before read futex */
246 wake_up_gp();
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247}
248
249static inline void _rcu_thread_online(void)
250{
ab179a17 251 _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
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252 smp_mb();
253}
254
255/**
256 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
257 * meant to be read by RCU read-side critical sections. Returns the assigned
258 * value.
259 *
260 * Documents which pointers will be dereferenced by RCU read-side critical
261 * sections and adds the required memory barriers on architectures requiring
262 * them. It also makes sure the compiler does not reorder code initializing the
263 * data structure before its publication.
264 *
265 * Should match rcu_dereference_pointer().
266 */
267
268#define _rcu_assign_pointer(p, v) \
269 ({ \
270 if (!__builtin_constant_p(v) || \
271 ((v) != NULL)) \
272 wmb(); \
273 STORE_SHARED(p, v); \
274 })
275
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276/**
277 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
278 * is as expected by "old". If succeeds, returns the previous pointer to the
279 * data structure, which can be safely freed after waiting for a quiescent state
280 * using synchronize_rcu(). If fails (unexpected value), returns old (which
281 * should not be freed !).
282 */
283
284#define _rcu_cmpxchg_pointer(p, old, _new) \
285 ({ \
286 if (!__builtin_constant_p(_new) || \
287 ((_new) != NULL)) \
288 wmb(); \
ec4e58a3 289 uatomic_cmpxchg(p, old, _new); \
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290 })
291
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292/**
293 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
294 * pointer to the data structure, which can be safely freed after waiting for a
295 * quiescent state using synchronize_rcu().
296 */
297
298#define _rcu_xchg_pointer(p, v) \
299 ({ \
300 if (!__builtin_constant_p(v) || \
301 ((v) != NULL)) \
302 wmb(); \
ec4e58a3 303 uatomic_xchg(p, v); \
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304 })
305
306/*
307 * Exchanges the pointer and waits for quiescent state.
308 * The pointer returned can be freed.
309 */
310#define _rcu_publish_content(p, v) \
311 ({ \
312 void *oldptr; \
313 oldptr = _rcu_xchg_pointer(p, v); \
314 synchronize_rcu(); \
315 oldptr; \
316 })
317
318#endif /* _URCU_QSBR_STATIC_H */
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