8e46820d7ae7436812f5ce8c9d1b1cc7d57f6900
[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 <limits.h>
35 #include <unistd.h>
36 #include <stdint.h>
37
38 #include <urcu/compiler.h>
39 #include <urcu/arch.h>
40 #include <urcu/system.h>
41 #include <urcu/uatomic.h>
42 #include <urcu/list.h>
43 #include <urcu/futex.h>
44 #include <urcu/tls-compat.h>
45 #include <urcu/debug.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 enum rcu_state {
60 RCU_READER_ACTIVE_CURRENT,
61 RCU_READER_ACTIVE_OLD,
62 RCU_READER_INACTIVE,
63 };
64
65 #define RCU_GP_ONLINE (1UL << 0)
66 #define RCU_GP_CTR (1UL << 1)
67
68 struct rcu_gp {
69 /*
70 * Global quiescent period counter with low-order bits unused.
71 * Using a int rather than a char to eliminate false register
72 * dependencies causing stalls on some architectures.
73 */
74 unsigned long ctr;
75
76 int32_t futex;
77 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
78
79 extern struct rcu_gp rcu_gp;
80
81 struct rcu_reader {
82 /* Data used by both reader and synchronize_rcu() */
83 unsigned long ctr;
84 /* Data used for registry */
85 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
86 int waiting;
87 pthread_t tid;
88 /* Reader registered flag, for internal checks. */
89 unsigned int registered:1;
90 };
91
92 extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
93
94 /*
95 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
96 */
97 static inline void wake_up_gp(void)
98 {
99 if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(rcu_reader).waiting))) {
100 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).waiting, 0);
101 cmm_smp_mb();
102 if (uatomic_read(&rcu_gp.futex) != -1)
103 return;
104 uatomic_set(&rcu_gp.futex, 0);
105 /*
106 * Ignoring return value until we can make this function
107 * return something (because urcu_die() is not publicly
108 * exposed).
109 */
110 (void) futex_noasync(&rcu_gp.futex, FUTEX_WAKE, 1,
111 NULL, NULL, 0);
112 }
113 }
114
115 static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
116 {
117 unsigned long v;
118
119 v = CMM_LOAD_SHARED(*ctr);
120 if (!v)
121 return RCU_READER_INACTIVE;
122 if (v == rcu_gp.ctr)
123 return RCU_READER_ACTIVE_CURRENT;
124 return RCU_READER_ACTIVE_OLD;
125 }
126
127 /*
128 * Enter an RCU read-side critical section.
129 *
130 * This function is less than 10 lines long. The intent is that this
131 * function meets the 10-line criterion for LGPL, allowing this function
132 * to be invoked directly from non-LGPL code.
133 */
134 static inline void _rcu_read_lock(void)
135 {
136 urcu_assert(URCU_TLS(rcu_reader).ctr);
137 }
138
139 /*
140 * Exit an RCU read-side critical section.
141 *
142 * This function is less than 10 lines long. The intent is that this
143 * function meets the 10-line criterion for LGPL, allowing this function
144 * to be invoked directly from non-LGPL code.
145 */
146 static inline void _rcu_read_unlock(void)
147 {
148 urcu_assert(URCU_TLS(rcu_reader).ctr);
149 }
150
151 /*
152 * Returns whether within a RCU read-side critical section.
153 *
154 * This function is less than 10 lines long. The intent is that this
155 * function meets the 10-line criterion for LGPL, allowing this function
156 * to be invoked directly from non-LGPL code.
157 */
158 static inline int _rcu_read_ongoing(void)
159 {
160 return URCU_TLS(rcu_reader).ctr;
161 }
162
163 /*
164 * This is a helper function for _rcu_quiescent_state().
165 * The first cmm_smp_mb() ensures memory accesses in the prior read-side
166 * critical sections are not reordered with store to
167 * URCU_TLS(rcu_reader).ctr, and ensures that mutexes held within an
168 * offline section that would happen to end with this
169 * rcu_quiescent_state() call are not reordered with
170 * store to URCU_TLS(rcu_reader).ctr.
171 */
172 static inline void _rcu_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
173 {
174 cmm_smp_mb();
175 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, gp_ctr);
176 cmm_smp_mb(); /* write URCU_TLS(rcu_reader).ctr before read futex */
177 wake_up_gp();
178 cmm_smp_mb();
179 }
180
181 /*
182 * Inform RCU of a quiescent state.
183 *
184 * This function is less than 10 lines long. The intent is that this
185 * function meets the 10-line criterion for LGPL, allowing this function
186 * to be invoked directly from non-LGPL code.
187 *
188 * We skip the memory barriers and gp store if our local ctr already
189 * matches the global rcu_gp.ctr value: this is OK because a prior
190 * _rcu_quiescent_state() or _rcu_thread_online() already updated it
191 * within our thread, so we have no quiescent state to report.
192 */
193 static inline void _rcu_quiescent_state(void)
194 {
195 unsigned long gp_ctr;
196
197 urcu_assert(URCU_TLS(rcu_reader).registered);
198 if ((gp_ctr = CMM_LOAD_SHARED(rcu_gp.ctr)) == URCU_TLS(rcu_reader).ctr)
199 return;
200 _rcu_quiescent_state_update_and_wakeup(gp_ctr);
201 }
202
203 /*
204 * Take a thread offline, prohibiting it from entering further RCU
205 * read-side critical sections.
206 *
207 * This function is less than 10 lines long. The intent is that this
208 * function meets the 10-line criterion for LGPL, allowing this function
209 * to be invoked directly from non-LGPL code.
210 */
211 static inline void _rcu_thread_offline(void)
212 {
213 urcu_assert(URCU_TLS(rcu_reader).registered);
214 cmm_smp_mb();
215 CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, 0);
216 cmm_smp_mb(); /* write URCU_TLS(rcu_reader).ctr before read futex */
217 wake_up_gp();
218 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
219 }
220
221 /*
222 * Bring a thread online, allowing it to once again enter RCU
223 * read-side critical sections.
224 *
225 * This function is less than 10 lines long. The intent is that this
226 * function meets the 10-line criterion for LGPL, allowing this function
227 * to be invoked directly from non-LGPL code.
228 */
229 static inline void _rcu_thread_online(void)
230 {
231 urcu_assert(URCU_TLS(rcu_reader).registered);
232 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
233 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, CMM_LOAD_SHARED(rcu_gp.ctr));
234 cmm_smp_mb();
235 }
236
237 #ifdef __cplusplus
238 }
239 #endif
240
241 #endif /* _URCU_QSBR_STATIC_H */
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