daa7ee2c31b6f7937f0e375d21deec556ad24593
[urcu.git] / include / urcu / static / urcu-qsbr.h
1 // SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2 // SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
3 //
4 // SPDX-License-Identifier: LGPL-2.1-or-later
5
6 #ifndef _URCU_QSBR_STATIC_H
7 #define _URCU_QSBR_STATIC_H
8
9 /*
10 * Userspace RCU QSBR header.
11 *
12 * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
13 * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
14 *
15 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
16 */
17
18 #include <stdlib.h>
19 #include <pthread.h>
20 #include <limits.h>
21 #include <unistd.h>
22 #include <stdint.h>
23
24 #include <urcu/debug.h>
25 #include <urcu/compiler.h>
26 #include <urcu/arch.h>
27 #include <urcu/system.h>
28 #include <urcu/uatomic.h>
29 #include <urcu/list.h>
30 #include <urcu/futex.h>
31 #include <urcu/tls-compat.h>
32 #include <urcu/static/urcu-common.h>
33
34 #ifdef __cplusplus
35 extern "C" {
36 #endif
37
38 /*
39 * This code section can only be included in LGPL 2.1 compatible source code.
40 * See below for the function call wrappers which can be used in code meant to
41 * be only linked with the Userspace RCU library. This comes with a small
42 * performance degradation on the read-side due to the added function calls.
43 * This is required to permit relinking with newer versions of the library.
44 */
45
46 #define URCU_QSBR_GP_ONLINE (1UL << 0)
47 #define URCU_QSBR_GP_CTR (1UL << 1)
48
49 extern struct urcu_gp urcu_qsbr_gp;
50
51 struct urcu_qsbr_reader {
52 /* Data used by both reader and synchronize_rcu() */
53 unsigned long ctr;
54 /* Data used for registry */
55 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
56 int waiting;
57 pthread_t tid;
58 /* Reader registered flag, for internal checks. */
59 unsigned int registered:1;
60 };
61
62 extern DECLARE_URCU_TLS(struct urcu_qsbr_reader, urcu_qsbr_reader);
63
64 /*
65 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
66 */
67 static inline void urcu_qsbr_wake_up_gp(void)
68 {
69 if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(urcu_qsbr_reader).waiting))) {
70 _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).waiting, 0);
71 cmm_smp_mb();
72 if (uatomic_read(&urcu_qsbr_gp.futex) != -1)
73 return;
74 uatomic_set(&urcu_qsbr_gp.futex, 0);
75 /*
76 * Ignoring return value until we can make this function
77 * return something (because urcu_die() is not publicly
78 * exposed).
79 */
80 (void) futex_noasync(&urcu_qsbr_gp.futex, FUTEX_WAKE, 1,
81 NULL, NULL, 0);
82 }
83 }
84
85 static inline enum urcu_state urcu_qsbr_reader_state(unsigned long *ctr)
86 {
87 unsigned long v;
88
89 v = CMM_LOAD_SHARED(*ctr);
90 if (!v)
91 return URCU_READER_INACTIVE;
92 if (v == urcu_qsbr_gp.ctr)
93 return URCU_READER_ACTIVE_CURRENT;
94 return URCU_READER_ACTIVE_OLD;
95 }
96
97 /*
98 * Enter an RCU read-side critical section.
99 *
100 * This function is less than 10 lines long. The intent is that this
101 * function meets the 10-line criterion for LGPL, allowing this function
102 * to be invoked directly from non-LGPL code.
103 */
104 static inline void _urcu_qsbr_read_lock(void)
105 {
106 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).ctr);
107 }
108
109 /*
110 * Exit an RCU read-side critical section.
111 *
112 * This function is less than 10 lines long. The intent is that this
113 * function meets the 10-line criterion for LGPL, allowing this function
114 * to be invoked directly from non-LGPL code.
115 */
116 static inline void _urcu_qsbr_read_unlock(void)
117 {
118 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).ctr);
119 }
120
121 /*
122 * Returns whether within a RCU read-side critical section.
123 *
124 * This function is less than 10 lines long. The intent is that this
125 * function meets the 10-line criterion for LGPL, allowing this function
126 * to be invoked directly from non-LGPL code.
127 */
128 static inline int _urcu_qsbr_read_ongoing(void)
129 {
130 return URCU_TLS(urcu_qsbr_reader).ctr;
131 }
132
133 /*
134 * This is a helper function for _rcu_quiescent_state().
135 * The first cmm_smp_mb() ensures memory accesses in the prior read-side
136 * critical sections are not reordered with store to
137 * URCU_TLS(urcu_qsbr_reader).ctr, and ensures that mutexes held within an
138 * offline section that would happen to end with this
139 * urcu_qsbr_quiescent_state() call are not reordered with
140 * store to URCU_TLS(urcu_qsbr_reader).ctr.
141 */
142 static inline void _urcu_qsbr_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
143 {
144 cmm_smp_mb();
145 _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).ctr, gp_ctr);
146 cmm_smp_mb(); /* write URCU_TLS(urcu_qsbr_reader).ctr before read futex */
147 urcu_qsbr_wake_up_gp();
148 cmm_smp_mb();
149 }
150
151 /*
152 * Inform RCU of a quiescent state.
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 * We skip the memory barriers and gp store if our local ctr already
159 * matches the global urcu_qsbr_gp.ctr value: this is OK because a prior
160 * _rcu_quiescent_state() or _rcu_thread_online() already updated it
161 * within our thread, so we have no quiescent state to report.
162 */
163 static inline void _urcu_qsbr_quiescent_state(void)
164 {
165 unsigned long gp_ctr;
166
167 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).registered);
168 if ((gp_ctr = CMM_LOAD_SHARED(urcu_qsbr_gp.ctr)) == URCU_TLS(urcu_qsbr_reader).ctr)
169 return;
170 _urcu_qsbr_quiescent_state_update_and_wakeup(gp_ctr);
171 }
172
173 /*
174 * Take a thread offline, prohibiting it from entering further RCU
175 * read-side critical sections.
176 *
177 * This function is less than 10 lines long. The intent is that this
178 * function meets the 10-line criterion for LGPL, allowing this function
179 * to be invoked directly from non-LGPL code.
180 */
181 static inline void _urcu_qsbr_thread_offline(void)
182 {
183 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).registered);
184 cmm_smp_mb();
185 CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).ctr, 0);
186 cmm_smp_mb(); /* write URCU_TLS(urcu_qsbr_reader).ctr before read futex */
187 urcu_qsbr_wake_up_gp();
188 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
189 }
190
191 /*
192 * Bring a thread online, allowing it to once again enter RCU
193 * read-side critical sections.
194 *
195 * This function is less than 10 lines long. The intent is that this
196 * function meets the 10-line criterion for LGPL, allowing this function
197 * to be invoked directly from non-LGPL code.
198 */
199 static inline void _urcu_qsbr_thread_online(void)
200 {
201 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader).registered);
202 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
203 _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader).ctr, CMM_LOAD_SHARED(urcu_qsbr_gp.ctr));
204 cmm_smp_mb();
205 }
206
207 #ifdef __cplusplus
208 }
209 #endif
210
211 #endif /* _URCU_QSBR_STATIC_H */
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