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[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@efficios.com>
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 #include <syscall.h>
37 #include <unistd.h>
38
39 #include <urcu/compiler.h>
40 #include <urcu/arch.h>
41 #include <urcu/system.h>
42 #include <urcu/uatomic_arch.h>
43 #include <urcu/list.h>
44 #include <urcu/urcu-futex.h>
45
46 #ifdef __cplusplus
47 extern "C" {
48 #endif
49
50 /*
51 * This code section can only be included in LGPL 2.1 compatible source code.
52 * See below for the function call wrappers which can be used in code meant to
53 * be only linked with the Userspace RCU library. This comes with a small
54 * performance degradation on the read-side due to the added function calls.
55 * This is required to permit relinking with newer versions of the library.
56 */
57
58 /*
59 * If a reader is really non-cooperative and refuses to commit its
60 * rcu_reader.ctr count to memory (there is no barrier in the reader
61 * per-se), kick it after a few loops waiting for it.
62 */
63 #define KICK_READER_LOOPS 10000
64
65 /*
66 * Active attempts to check for reader Q.S. before calling futex().
67 */
68 #define RCU_QS_ACTIVE_ATTEMPTS 100
69
70 #ifdef DEBUG_RCU
71 #define rcu_assert(args...) assert(args)
72 #else
73 #define rcu_assert(args...)
74 #endif
75
76 #ifdef DEBUG_YIELD
77 #include <sched.h>
78 #include <time.h>
79 #include <pthread.h>
80 #include <unistd.h>
81
82 #define YIELD_READ (1 << 0)
83 #define YIELD_WRITE (1 << 1)
84
85 /* maximum sleep delay, in us */
86 #define MAX_SLEEP 50
87
88 extern unsigned int yield_active;
89 extern unsigned int __thread rand_yield;
90
91 static inline void debug_yield_read(void)
92 {
93 if (yield_active & YIELD_READ)
94 if (rand_r(&rand_yield) & 0x1)
95 usleep(rand_r(&rand_yield) % MAX_SLEEP);
96 }
97
98 static inline void debug_yield_write(void)
99 {
100 if (yield_active & YIELD_WRITE)
101 if (rand_r(&rand_yield) & 0x1)
102 usleep(rand_r(&rand_yield) % MAX_SLEEP);
103 }
104
105 static inline void debug_yield_init(void)
106 {
107 rand_yield = time(NULL) ^ pthread_self();
108 }
109 #else
110 static inline void debug_yield_read(void)
111 {
112 }
113
114 static inline void debug_yield_write(void)
115 {
116 }
117
118 static inline void debug_yield_init(void)
119 {
120
121 }
122 #endif
123
124 #define RCU_GP_ONLINE (1UL << 0)
125 #define RCU_GP_CTR (1UL << 1)
126
127 /*
128 * Global quiescent period counter with low-order bits unused.
129 * Using a int rather than a char to eliminate false register dependencies
130 * causing stalls on some architectures.
131 */
132 extern unsigned long rcu_gp_ctr;
133
134 struct rcu_reader {
135 /* Data used by both reader and synchronize_rcu() */
136 unsigned long ctr;
137 /* Data used for registry */
138 struct list_head node __attribute__((aligned(CACHE_LINE_SIZE)));
139 pthread_t tid;
140 };
141
142 extern struct rcu_reader __thread rcu_reader;
143
144 extern int gp_futex;
145
146 /*
147 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
148 */
149 static inline void wake_up_gp(void)
150 {
151 if (unlikely(uatomic_read(&gp_futex) == -1)) {
152 uatomic_set(&gp_futex, 0);
153 futex_noasync(&gp_futex, FUTEX_WAKE, 1,
154 NULL, NULL, 0);
155 }
156 }
157
158 static inline int rcu_gp_ongoing(unsigned long *ctr)
159 {
160 unsigned long v;
161
162 v = LOAD_SHARED(*ctr);
163 return v && (v != rcu_gp_ctr);
164 }
165
166 static inline void _rcu_read_lock(void)
167 {
168 rcu_assert(rcu_reader.ctr);
169 }
170
171 static inline void _rcu_read_unlock(void)
172 {
173 }
174
175 static inline void _rcu_quiescent_state(void)
176 {
177 smp_mb();
178 _STORE_SHARED(rcu_reader.ctr, _LOAD_SHARED(rcu_gp_ctr));
179 smp_mb(); /* write rcu_reader.ctr before read futex */
180 wake_up_gp();
181 smp_mb();
182 }
183
184 static inline void _rcu_thread_offline(void)
185 {
186 smp_mb();
187 STORE_SHARED(rcu_reader.ctr, 0);
188 smp_mb(); /* write rcu_reader.ctr before read futex */
189 wake_up_gp();
190 }
191
192 static inline void _rcu_thread_online(void)
193 {
194 _STORE_SHARED(rcu_reader.ctr, LOAD_SHARED(rcu_gp_ctr));
195 smp_mb();
196 }
197
198 #ifdef __cplusplus
199 }
200 #endif
201
202 #endif /* _URCU_QSBR_STATIC_H */
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