30bd7fddbea5372c08aff936751e79225893a314
[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/arch_uatomic.h>
41 #include <urcu/list.h>
42
43 #define futex(...) syscall(__NR_futex, __VA_ARGS__)
44 #define FUTEX_WAIT 0
45 #define FUTEX_WAKE 1
46
47 /*
48 * This code section can only be included in LGPL 2.1 compatible source code.
49 * See below for the function call wrappers which can be used in code meant to
50 * be only linked with the Userspace RCU library. This comes with a small
51 * performance degradation on the read-side due to the added function calls.
52 * This is required to permit relinking with newer versions of the library.
53 */
54
55 /*
56 * The signal number used by the RCU library can be overridden with
57 * -DSIGURCU= when compiling the library.
58 */
59 #ifndef SIGURCU
60 #define SIGURCU SIGUSR1
61 #endif
62
63 /*
64 * If a reader is really non-cooperative and refuses to commit its
65 * urcu_active_readers count to memory (there is no barrier in the reader
66 * per-se), kick it after a few loops waiting for it.
67 */
68 #define KICK_READER_LOOPS 10000
69
70 /*
71 * Active attempts to check for reader Q.S. before calling futex().
72 */
73 #define RCU_QS_ACTIVE_ATTEMPTS 100
74
75 #ifdef DEBUG_RCU
76 #define rcu_assert(args...) assert(args)
77 #else
78 #define rcu_assert(args...)
79 #endif
80
81 #ifdef DEBUG_YIELD
82 #include <sched.h>
83 #include <time.h>
84 #include <pthread.h>
85 #include <unistd.h>
86
87 #define YIELD_READ (1 << 0)
88 #define YIELD_WRITE (1 << 1)
89
90 /*
91 * Updates without URCU_MB are much slower. Account this in
92 * the delay.
93 */
94 #ifdef URCU_MB
95 /* maximum sleep delay, in us */
96 #define MAX_SLEEP 50
97 #else
98 #define MAX_SLEEP 30000
99 #endif
100
101 extern unsigned int yield_active;
102 extern unsigned int __thread rand_yield;
103
104 static inline void debug_yield_read(void)
105 {
106 if (yield_active & YIELD_READ)
107 if (rand_r(&rand_yield) & 0x1)
108 usleep(rand_r(&rand_yield) % MAX_SLEEP);
109 }
110
111 static inline void debug_yield_write(void)
112 {
113 if (yield_active & YIELD_WRITE)
114 if (rand_r(&rand_yield) & 0x1)
115 usleep(rand_r(&rand_yield) % MAX_SLEEP);
116 }
117
118 static inline void debug_yield_init(void)
119 {
120 rand_yield = time(NULL) ^ pthread_self();
121 }
122 #else
123 static inline void debug_yield_read(void)
124 {
125 }
126
127 static inline void debug_yield_write(void)
128 {
129 }
130
131 static inline void debug_yield_init(void)
132 {
133
134 }
135 #endif
136
137 #ifdef URCU_MB
138 static inline void reader_barrier()
139 {
140 smp_mb();
141 }
142 #else
143 static inline void reader_barrier()
144 {
145 barrier();
146 }
147 #endif
148
149 /*
150 * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
151 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
152 */
153 #define RCU_GP_COUNT (1UL << 0)
154 /* Use the amount of bits equal to half of the architecture long size */
155 #define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
156 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
157
158 /*
159 * Global quiescent period counter with low-order bits unused.
160 * Using a int rather than a char to eliminate false register dependencies
161 * causing stalls on some architectures.
162 */
163 extern long urcu_gp_ctr;
164
165 struct urcu_reader {
166 /* Data used by both reader and synchronize_rcu() */
167 long ctr;
168 char need_mb;
169 /* Data used for registry */
170 struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
171 pthread_t tid;
172 };
173
174 extern struct urcu_reader __thread urcu_reader;
175
176 extern int gp_futex;
177
178 /*
179 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
180 */
181 static inline void wake_up_gp(void)
182 {
183 if (unlikely(uatomic_read(&gp_futex) == -1)) {
184 uatomic_set(&gp_futex, 0);
185 futex(&gp_futex, FUTEX_WAKE, 1,
186 NULL, NULL, 0);
187 }
188 }
189
190 static inline int rcu_old_gp_ongoing(long *value)
191 {
192 long v;
193
194 if (value == NULL)
195 return 0;
196 /*
197 * Make sure both tests below are done on the same version of *value
198 * to insure consistency.
199 */
200 v = LOAD_SHARED(*value);
201 return (v & RCU_GP_CTR_NEST_MASK) &&
202 ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
203 }
204
205 static inline void _rcu_read_lock(void)
206 {
207 long tmp;
208
209 tmp = urcu_reader.ctr;
210 /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
211 if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
212 _STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_gp_ctr));
213 /*
214 * Set active readers count for outermost nesting level before
215 * accessing the pointer. See force_mb_all_threads().
216 */
217 reader_barrier();
218 } else {
219 _STORE_SHARED(urcu_reader.ctr, tmp + RCU_GP_COUNT);
220 }
221 }
222
223 static inline void _rcu_read_unlock(void)
224 {
225 long tmp;
226
227 tmp = urcu_reader.ctr;
228 /*
229 * Finish using rcu before decrementing the pointer.
230 * See force_mb_all_threads().
231 */
232 if (likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
233 reader_barrier();
234 _STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
235 /* write urcu_reader.ctr before read futex */
236 reader_barrier();
237 wake_up_gp();
238 } else {
239 _STORE_SHARED(urcu_reader.ctr, urcu_reader.ctr - RCU_GP_COUNT);
240 }
241 }
242
243 #endif /* _URCU_STATIC_H */
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