Add extern "C" to support linking userspace RCU library with C++ applications
[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 <urcu/compiler.h>
38 #include <urcu/arch.h>
39 #include <urcu/system.h>
40 #include <urcu/uatomic_arch.h>
41 #include <urcu/list.h>
42 #include <urcu/urcu-futex.h>
43
44 #ifdef __cplusplus
45 extern "C" {
46 #endif
47
48 /*
49 * This code section can only be included in LGPL 2.1 compatible source code.
50 * See below for the function call wrappers which can be used in code meant to
51 * be only linked with the Userspace RCU library. This comes with a small
52 * performance degradation on the read-side due to the added function calls.
53 * This is required to permit relinking with newer versions of the library.
54 */
55
56 /*
57 * The signal number used by the RCU library can be overridden with
58 * -DSIGURCU= when compiling the library.
59 */
60 #ifndef SIGURCU
61 #define SIGURCU SIGUSR1
62 #endif
63
64 /*
65 * If a reader is really non-cooperative and refuses to commit its
66 * urcu_active_readers count to memory (there is no barrier in the reader
67 * per-se), kick it after a few loops waiting for it.
68 */
69 #define KICK_READER_LOOPS 10000
70
71 /*
72 * Active attempts to check for reader Q.S. before calling futex().
73 */
74 #define RCU_QS_ACTIVE_ATTEMPTS 100
75
76 #ifdef DEBUG_RCU
77 #define rcu_assert(args...) assert(args)
78 #else
79 #define rcu_assert(args...)
80 #endif
81
82 #ifdef DEBUG_YIELD
83 #include <sched.h>
84 #include <time.h>
85 #include <pthread.h>
86 #include <unistd.h>
87
88 #define YIELD_READ (1 << 0)
89 #define YIELD_WRITE (1 << 1)
90
91 /*
92 * Updates without URCU_MB are much slower. Account this in
93 * the delay.
94 */
95 #ifdef URCU_MB
96 /* maximum sleep delay, in us */
97 #define MAX_SLEEP 50
98 #else
99 #define MAX_SLEEP 30000
100 #endif
101
102 extern unsigned int yield_active;
103 extern unsigned int __thread rand_yield;
104
105 static inline void debug_yield_read(void)
106 {
107 if (yield_active & YIELD_READ)
108 if (rand_r(&rand_yield) & 0x1)
109 usleep(rand_r(&rand_yield) % MAX_SLEEP);
110 }
111
112 static inline void debug_yield_write(void)
113 {
114 if (yield_active & YIELD_WRITE)
115 if (rand_r(&rand_yield) & 0x1)
116 usleep(rand_r(&rand_yield) % MAX_SLEEP);
117 }
118
119 static inline void debug_yield_init(void)
120 {
121 rand_yield = time(NULL) ^ pthread_self();
122 }
123 #else
124 static inline void debug_yield_read(void)
125 {
126 }
127
128 static inline void debug_yield_write(void)
129 {
130 }
131
132 static inline void debug_yield_init(void)
133 {
134
135 }
136 #endif
137
138 #ifdef URCU_MB
139 static inline void reader_barrier()
140 {
141 smp_mb();
142 }
143 #else
144 static inline void reader_barrier()
145 {
146 barrier();
147 }
148 #endif
149
150 /*
151 * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
152 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
153 */
154 #define RCU_GP_COUNT (1UL << 0)
155 /* Use the amount of bits equal to half of the architecture long size */
156 #define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
157 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
158
159 /*
160 * Global quiescent period counter with low-order bits unused.
161 * Using a int rather than a char to eliminate false register dependencies
162 * causing stalls on some architectures.
163 */
164 extern long urcu_gp_ctr;
165
166 struct urcu_reader {
167 /* Data used by both reader and synchronize_rcu() */
168 long ctr;
169 char need_mb;
170 /* Data used for registry */
171 struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
172 pthread_t tid;
173 };
174
175 extern struct urcu_reader __thread urcu_reader;
176
177 extern int gp_futex;
178
179 /*
180 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
181 */
182 static inline void wake_up_gp(void)
183 {
184 if (unlikely(uatomic_read(&gp_futex) == -1)) {
185 uatomic_set(&gp_futex, 0);
186 futex_async(&gp_futex, FUTEX_WAKE, 1,
187 NULL, NULL, 0);
188 }
189 }
190
191 static inline int rcu_old_gp_ongoing(long *value)
192 {
193 long v;
194
195 if (value == NULL)
196 return 0;
197 /*
198 * Make sure both tests below are done on the same version of *value
199 * to insure consistency.
200 */
201 v = LOAD_SHARED(*value);
202 return (v & RCU_GP_CTR_NEST_MASK) &&
203 ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
204 }
205
206 static inline void _rcu_read_lock(void)
207 {
208 long tmp;
209
210 tmp = urcu_reader.ctr;
211 /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
212 if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
213 _STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_gp_ctr));
214 /*
215 * Set active readers count for outermost nesting level before
216 * accessing the pointer. See force_mb_all_threads().
217 */
218 reader_barrier();
219 } else {
220 _STORE_SHARED(urcu_reader.ctr, tmp + RCU_GP_COUNT);
221 }
222 }
223
224 static inline void _rcu_read_unlock(void)
225 {
226 long tmp;
227
228 tmp = urcu_reader.ctr;
229 /*
230 * Finish using rcu before decrementing the pointer.
231 * See force_mb_all_threads().
232 */
233 if (likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
234 reader_barrier();
235 _STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
236 /* write urcu_reader.ctr before read futex */
237 reader_barrier();
238 wake_up_gp();
239 } else {
240 _STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
241 }
242 }
243
244 #ifdef __cplusplus
245 }
246 #endif
247
248 #endif /* _URCU_STATIC_H */
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