Add rcu_read_ongoing() API to each urcu flavor
[urcu.git] / urcu / static / urcu-qsbr.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 CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
10 * RELEASE. See urcu.h for linking dynamically with the userspace rcu 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 <unistd.h>
37 #include <stdint.h>
38
39 #include <urcu/compiler.h>
40 #include <urcu/arch.h>
41 #include <urcu/system.h>
42 #include <urcu/uatomic.h>
43 #include <urcu/list.h>
44 #include <urcu/futex.h>
45 #include <urcu/tls-compat.h>
46
47 #ifdef __cplusplus
48 extern "C" {
49 #endif
50
51 /*
52 * This code section can only be included in LGPL 2.1 compatible source code.
53 * See below for the function call wrappers which can be used in code meant to
54 * be only linked with the Userspace RCU library. This comes with a small
55 * performance degradation on the read-side due to the added function calls.
56 * This is required to permit relinking with newer versions of the library.
57 */
58
59 #ifdef DEBUG_RCU
60 #define rcu_assert(args...) assert(args)
61 #else
62 #define rcu_assert(args...)
63 #endif
64
65 enum rcu_state {
66 RCU_READER_ACTIVE_CURRENT,
67 RCU_READER_ACTIVE_OLD,
68 RCU_READER_INACTIVE,
69 };
70
71 #ifdef DEBUG_YIELD
72 #include <sched.h>
73 #include <time.h>
74 #include <pthread.h>
75 #include <unistd.h>
76
77 #define RCU_YIELD_READ (1 << 0)
78 #define RCU_YIELD_WRITE (1 << 1)
79
80 /* maximum sleep delay, in us */
81 #define MAX_SLEEP 50
82
83 extern unsigned int rcu_yield_active;
84 extern DECLARE_URCU_TLS(unsigned int, rcu_rand_yield);
85
86 static inline void rcu_debug_yield_read(void)
87 {
88 if (rcu_yield_active & RCU_YIELD_READ)
89 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
90 usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
91 }
92
93 static inline void rcu_debug_yield_write(void)
94 {
95 if (rcu_yield_active & RCU_YIELD_WRITE)
96 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
97 usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
98 }
99
100 static inline void rcu_debug_yield_init(void)
101 {
102 URCU_TLS(rcu_rand_yield) = time(NULL) ^ (unsigned long) pthread_self();
103 }
104 #else
105 static inline void rcu_debug_yield_read(void)
106 {
107 }
108
109 static inline void rcu_debug_yield_write(void)
110 {
111 }
112
113 static inline void rcu_debug_yield_init(void)
114 {
115
116 }
117 #endif
118
119 #define RCU_GP_ONLINE (1UL << 0)
120 #define RCU_GP_CTR (1UL << 1)
121
122 /*
123 * Global quiescent period counter with low-order bits unused.
124 * Using a int rather than a char to eliminate false register dependencies
125 * causing stalls on some architectures.
126 */
127 extern unsigned long rcu_gp_ctr;
128
129 struct rcu_reader {
130 /* Data used by both reader and synchronize_rcu() */
131 unsigned long ctr;
132 /* Data used for registry */
133 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
134 int waiting;
135 pthread_t tid;
136 };
137
138 extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
139
140 extern int32_t rcu_gp_futex;
141
142 /*
143 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
144 */
145 static inline void wake_up_gp(void)
146 {
147 if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(rcu_reader).waiting))) {
148 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).waiting, 0);
149 cmm_smp_mb();
150 if (uatomic_read(&rcu_gp_futex) != -1)
151 return;
152 uatomic_set(&rcu_gp_futex, 0);
153 futex_noasync(&rcu_gp_futex, FUTEX_WAKE, 1,
154 NULL, NULL, 0);
155 }
156 }
157
158 static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
159 {
160 unsigned long v;
161
162 v = CMM_LOAD_SHARED(*ctr);
163 if (!v)
164 return RCU_READER_INACTIVE;
165 if (v == rcu_gp_ctr)
166 return RCU_READER_ACTIVE_CURRENT;
167 return RCU_READER_ACTIVE_OLD;
168 }
169
170 /*
171 * Enter an RCU read-side critical section.
172 *
173 * This function is less than 10 lines long. The intent is that this
174 * function meets the 10-line criterion for LGPL, allowing this function
175 * to be invoked directly from non-LGPL code.
176 */
177 static inline void _rcu_read_lock(void)
178 {
179 rcu_assert(URCU_TLS(rcu_reader).ctr);
180 }
181
182 /*
183 * Exit an RCU read-side critical section.
184 *
185 * This function is less than 10 lines long. The intent is that this
186 * function meets the 10-line criterion for LGPL, allowing this function
187 * to be invoked directly from non-LGPL code.
188 */
189 static inline void _rcu_read_unlock(void)
190 {
191 }
192
193 /*
194 * Returns whether within a RCU read-side critical section.
195 *
196 * This function is less than 10 lines long. The intent is that this
197 * function meets the 10-line criterion for LGPL, allowing this function
198 * to be invoked directly from non-LGPL code.
199 */
200 static inline int _rcu_read_ongoing(void)
201 {
202 return URCU_TLS(rcu_reader).ctr;
203 }
204
205 /*
206 * This is a helper function for _rcu_quiescent_state().
207 * The first cmm_smp_mb() ensures memory accesses in the prior read-side
208 * critical sections are not reordered with store to
209 * URCU_TLS(rcu_reader).ctr, and ensures that mutexes held within an
210 * offline section that would happen to end with this
211 * rcu_quiescent_state() call are not reordered with
212 * store to URCU_TLS(rcu_reader).ctr.
213 */
214 static inline void _rcu_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
215 {
216 cmm_smp_mb();
217 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, gp_ctr);
218 cmm_smp_mb(); /* write URCU_TLS(rcu_reader).ctr before read futex */
219 wake_up_gp();
220 cmm_smp_mb();
221 }
222
223 /*
224 * Inform RCU of a quiescent state.
225 *
226 * This function is less than 10 lines long. The intent is that this
227 * function meets the 10-line criterion for LGPL, allowing this function
228 * to be invoked directly from non-LGPL code.
229 *
230 * We skip the memory barriers and gp store if our local ctr already
231 * matches the global rcu_gp_ctr value: this is OK because a prior
232 * _rcu_quiescent_state() or _rcu_thread_online() already updated it
233 * within our thread, so we have no quiescent state to report.
234 */
235 static inline void _rcu_quiescent_state(void)
236 {
237 unsigned long gp_ctr;
238
239 if ((gp_ctr = CMM_LOAD_SHARED(rcu_gp_ctr)) == URCU_TLS(rcu_reader).ctr)
240 return;
241 _rcu_quiescent_state_update_and_wakeup(gp_ctr);
242 }
243
244 /*
245 * Take a thread offline, prohibiting it from entering further RCU
246 * read-side critical sections.
247 *
248 * This function is less than 10 lines long. The intent is that this
249 * function meets the 10-line criterion for LGPL, allowing this function
250 * to be invoked directly from non-LGPL code.
251 */
252 static inline void _rcu_thread_offline(void)
253 {
254 cmm_smp_mb();
255 CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, 0);
256 cmm_smp_mb(); /* write URCU_TLS(rcu_reader).ctr before read futex */
257 wake_up_gp();
258 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
259 }
260
261 /*
262 * Bring a thread online, allowing it to once again enter RCU
263 * read-side critical sections.
264 *
265 * This function is less than 10 lines long. The intent is that this
266 * function meets the 10-line criterion for LGPL, allowing this function
267 * to be invoked directly from non-LGPL code.
268 */
269 static inline void _rcu_thread_online(void)
270 {
271 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
272 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, CMM_LOAD_SHARED(rcu_gp_ctr));
273 cmm_smp_mb();
274 }
275
276 #ifdef __cplusplus
277 }
278 #endif
279
280 #endif /* _URCU_QSBR_STATIC_H */
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