a6063e2de2de78f1f7a0da84f004b790825ad118
[urcu.git] / include / 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 #include <urcu/static/urcu-common.h>
47
48 #ifdef __cplusplus
49 extern "C" {
50 #endif
51
52 /*
53 * This code section can only be included in LGPL 2.1 compatible source code.
54 * See below for the function call wrappers which can be used in code meant to
55 * be only linked with the Userspace RCU library. This comes with a small
56 * performance degradation on the read-side due to the added function calls.
57 * This is required to permit relinking with newer versions of the library.
58 */
59
60 #define URCU_QSBR_GP_ONLINE (1UL << 0)
61 #define URCU_QSBR_GP_CTR (1UL << 1)
62
63 extern struct urcu_gp urcu_qsbr_gp;
64
65 struct urcu_qsbr_reader {
66 /* Data used by both reader and synchronize_rcu() */
67 unsigned long ctr;
68 /* Data used for registry */
69 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
70 int waiting;
71 pthread_t tid;
72 /* Reader registered flag, for internal checks. */
73 unsigned int registered:1;
74 };
75
76 extern DECLARE_URCU_TLS(struct urcu_qsbr_reader, urcu_qsbr_reader);
77
78 /*
79 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
80 */
81 static inline void urcu_qsbr_wake_up_gp(void)
82 {
83 if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(urcu_qsbr_reader).waiting))) {
84 _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).waiting, 0);
85 cmm_smp_mb();
86 if (uatomic_read(&urcu_qsbr_gp.futex) != -1)
87 return;
88 uatomic_set(&urcu_qsbr_gp.futex, 0);
89 /*
90 * Ignoring return value until we can make this function
91 * return something (because urcu_die() is not publicly
92 * exposed).
93 */
94 (void) futex_noasync(&urcu_qsbr_gp.futex, FUTEX_WAKE, 1,
95 NULL, NULL, 0);
96 }
97 }
98
99 static inline enum urcu_state urcu_qsbr_reader_state(unsigned long *ctr)
100 {
101 unsigned long v;
102
103 v = CMM_LOAD_SHARED(*ctr);
104 if (!v)
105 return URCU_READER_INACTIVE;
106 if (v == urcu_qsbr_gp.ctr)
107 return URCU_READER_ACTIVE_CURRENT;
108 return URCU_READER_ACTIVE_OLD;
109 }
110
111 /*
112 * Enter an RCU read-side critical section.
113 *
114 * This function is less than 10 lines long. The intent is that this
115 * function meets the 10-line criterion for LGPL, allowing this function
116 * to be invoked directly from non-LGPL code.
117 */
118 static inline void _urcu_qsbr_read_lock(void)
119 {
120 urcu_assert(URCU_TLS(urcu_qsbr_reader).ctr);
121 }
122
123 /*
124 * Exit an RCU read-side critical section.
125 *
126 * This function is less than 10 lines long. The intent is that this
127 * function meets the 10-line criterion for LGPL, allowing this function
128 * to be invoked directly from non-LGPL code.
129 */
130 static inline void _urcu_qsbr_read_unlock(void)
131 {
132 urcu_assert(URCU_TLS(urcu_qsbr_reader).ctr);
133 }
134
135 /*
136 * Returns whether within a RCU read-side critical section.
137 *
138 * This function is less than 10 lines long. The intent is that this
139 * function meets the 10-line criterion for LGPL, allowing this function
140 * to be invoked directly from non-LGPL code.
141 */
142 static inline int _urcu_qsbr_read_ongoing(void)
143 {
144 return URCU_TLS(urcu_qsbr_reader).ctr;
145 }
146
147 /*
148 * This is a helper function for _rcu_quiescent_state().
149 * The first cmm_smp_mb() ensures memory accesses in the prior read-side
150 * critical sections are not reordered with store to
151 * URCU_TLS(urcu_qsbr_reader).ctr, and ensures that mutexes held within an
152 * offline section that would happen to end with this
153 * urcu_qsbr_quiescent_state() call are not reordered with
154 * store to URCU_TLS(urcu_qsbr_reader).ctr.
155 */
156 static inline void _urcu_qsbr_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
157 {
158 cmm_smp_mb();
159 _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).ctr, gp_ctr);
160 cmm_smp_mb(); /* write URCU_TLS(urcu_qsbr_reader).ctr before read futex */
161 urcu_qsbr_wake_up_gp();
162 cmm_smp_mb();
163 }
164
165 /*
166 * Inform RCU of a quiescent state.
167 *
168 * This function is less than 10 lines long. The intent is that this
169 * function meets the 10-line criterion for LGPL, allowing this function
170 * to be invoked directly from non-LGPL code.
171 *
172 * We skip the memory barriers and gp store if our local ctr already
173 * matches the global urcu_qsbr_gp.ctr value: this is OK because a prior
174 * _rcu_quiescent_state() or _rcu_thread_online() already updated it
175 * within our thread, so we have no quiescent state to report.
176 */
177 static inline void _urcu_qsbr_quiescent_state(void)
178 {
179 unsigned long gp_ctr;
180
181 urcu_assert(URCU_TLS(urcu_qsbr_reader).registered);
182 if ((gp_ctr = CMM_LOAD_SHARED(urcu_qsbr_gp.ctr)) == URCU_TLS(urcu_qsbr_reader).ctr)
183 return;
184 _urcu_qsbr_quiescent_state_update_and_wakeup(gp_ctr);
185 }
186
187 /*
188 * Take a thread offline, prohibiting it from entering further RCU
189 * read-side critical sections.
190 *
191 * This function is less than 10 lines long. The intent is that this
192 * function meets the 10-line criterion for LGPL, allowing this function
193 * to be invoked directly from non-LGPL code.
194 */
195 static inline void _urcu_qsbr_thread_offline(void)
196 {
197 urcu_assert(URCU_TLS(urcu_qsbr_reader).registered);
198 cmm_smp_mb();
199 CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).ctr, 0);
200 cmm_smp_mb(); /* write URCU_TLS(urcu_qsbr_reader).ctr before read futex */
201 urcu_qsbr_wake_up_gp();
202 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
203 }
204
205 /*
206 * Bring a thread online, allowing it to once again enter RCU
207 * read-side critical sections.
208 *
209 * This function is less than 10 lines long. The intent is that this
210 * function meets the 10-line criterion for LGPL, allowing this function
211 * to be invoked directly from non-LGPL code.
212 */
213 static inline void _urcu_qsbr_thread_online(void)
214 {
215 urcu_assert(URCU_TLS(urcu_qsbr_reader).registered);
216 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
217 _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).ctr, CMM_LOAD_SHARED(urcu_qsbr_gp.ctr));
218 cmm_smp_mb();
219 }
220
221 #ifdef __cplusplus
222 }
223 #endif
224
225 #endif /* _URCU_QSBR_STATIC_H */
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