Allow forcing the use of sys membarrier
[urcu.git] / include / urcu / static / urcu.h
1 #ifndef _URCU_STATIC_H
2 #define _URCU_STATIC_H
3
4 /*
5 * urcu-static.h
6 *
7 * Userspace RCU 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 <unistd.h>
35 #include <stdint.h>
36
37 #include <urcu/config.h>
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 /* Default is RCU_MEMBARRIER */
52 #if !defined(RCU_MEMBARRIER) && !defined(RCU_MB) && !defined(RCU_SIGNAL)
53 #define RCU_MEMBARRIER
54 #endif
55
56 /*
57 * This code section can only be included in LGPL 2.1 compatible source code.
58 * See below for the function call wrappers which can be used in code meant to
59 * be only linked with the Userspace RCU library. This comes with a small
60 * performance degradation on the read-side due to the added function calls.
61 * This is required to permit relinking with newer versions of the library.
62 */
63
64 /*
65 * The signal number used by the RCU library can be overridden with
66 * -DSIGRCU= when compiling the library.
67 * Provide backward compatibility for liburcu 0.3.x SIGURCU.
68 */
69 #ifdef SIGURCU
70 #define SIGRCU SIGURCU
71 #endif
72
73 #ifndef SIGRCU
74 #define SIGRCU SIGUSR1
75 #endif
76
77 enum rcu_state {
78 RCU_READER_ACTIVE_CURRENT,
79 RCU_READER_ACTIVE_OLD,
80 RCU_READER_INACTIVE,
81 };
82
83 /*
84 * Slave barriers are only guaranteed to be ordered wrt master barriers.
85 *
86 * The pair ordering is detailed as (O: ordered, X: not ordered) :
87 * slave master
88 * slave X O
89 * master O O
90 */
91
92 #ifdef RCU_MEMBARRIER
93 #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
94 #define rcu_has_sys_membarrier_memb 1
95 #else
96 extern int rcu_has_sys_membarrier_memb;
97 #endif
98
99 static inline void smp_mb_slave(void)
100 {
101 if (caa_likely(rcu_has_sys_membarrier_memb))
102 cmm_barrier();
103 else
104 cmm_smp_mb();
105 }
106 #endif
107
108 #ifdef RCU_MB
109 static inline void smp_mb_slave(void)
110 {
111 cmm_smp_mb();
112 }
113 #endif
114
115 #ifdef RCU_SIGNAL
116 static inline void smp_mb_slave(void)
117 {
118 cmm_barrier();
119 }
120 #endif
121
122 /*
123 * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use
124 * a full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
125 */
126 #define RCU_GP_COUNT (1UL << 0)
127 /* Use the amount of bits equal to half of the architecture long size */
128 #define RCU_GP_CTR_PHASE (1UL << (sizeof(unsigned long) << 2))
129 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_PHASE - 1)
130
131 struct rcu_gp {
132 /*
133 * Global grace period counter.
134 * Contains the current RCU_GP_CTR_PHASE.
135 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
136 * Written to only by writer with mutex taken.
137 * Read by both writer and readers.
138 */
139 unsigned long ctr;
140
141 int32_t futex;
142 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
143
144 extern struct rcu_gp rcu_gp;
145
146 struct rcu_reader {
147 /* Data used by both reader and synchronize_rcu() */
148 unsigned long ctr;
149 char need_mb;
150 /* Data used for registry */
151 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
152 pthread_t tid;
153 /* Reader registered flag, for internal checks. */
154 unsigned int registered:1;
155 };
156
157 extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
158
159 /*
160 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
161 */
162 static inline void wake_up_gp(void)
163 {
164 if (caa_unlikely(uatomic_read(&rcu_gp.futex) == -1)) {
165 uatomic_set(&rcu_gp.futex, 0);
166 /*
167 * Ignoring return value until we can make this function
168 * return something (because urcu_die() is not publicly
169 * exposed).
170 */
171 (void) futex_async(&rcu_gp.futex, FUTEX_WAKE, 1,
172 NULL, NULL, 0);
173 }
174 }
175
176 static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
177 {
178 unsigned long v;
179
180 /*
181 * Make sure both tests below are done on the same version of *value
182 * to insure consistency.
183 */
184 v = CMM_LOAD_SHARED(*ctr);
185 if (!(v & RCU_GP_CTR_NEST_MASK))
186 return RCU_READER_INACTIVE;
187 if (!((v ^ rcu_gp.ctr) & RCU_GP_CTR_PHASE))
188 return RCU_READER_ACTIVE_CURRENT;
189 return RCU_READER_ACTIVE_OLD;
190 }
191
192 /*
193 * Helper for _rcu_read_lock(). The format of rcu_gp.ctr (as well as
194 * the per-thread rcu_reader.ctr) has the upper bits containing a count of
195 * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
196 * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in
197 * _rcu_read_lock() happen before the subsequent read-side critical section.
198 */
199 static inline void _rcu_read_lock_update(unsigned long tmp)
200 {
201 if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
202 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, _CMM_LOAD_SHARED(rcu_gp.ctr));
203 smp_mb_slave();
204 } else
205 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp + RCU_GP_COUNT);
206 }
207
208 /*
209 * Enter an RCU read-side critical section.
210 *
211 * The first cmm_barrier() call ensures that the compiler does not reorder
212 * the body of _rcu_read_lock() with a mutex.
213 *
214 * This function and its helper are both less than 10 lines long. The
215 * intent is that this function meets the 10-line criterion in LGPL,
216 * allowing this function to be invoked directly from non-LGPL code.
217 */
218 static inline void _rcu_read_lock(void)
219 {
220 unsigned long tmp;
221
222 urcu_assert(URCU_TLS(rcu_reader).registered);
223 cmm_barrier();
224 tmp = URCU_TLS(rcu_reader).ctr;
225 urcu_assert((tmp & RCU_GP_CTR_NEST_MASK) != RCU_GP_CTR_NEST_MASK);
226 _rcu_read_lock_update(tmp);
227 }
228
229 /*
230 * This is a helper function for _rcu_read_unlock().
231 *
232 * The first smp_mb_slave() call ensures that the critical section is
233 * seen to precede the store to rcu_reader.ctr.
234 * The second smp_mb_slave() call ensures that we write to rcu_reader.ctr
235 * before reading the update-side futex.
236 */
237 static inline void _rcu_read_unlock_update_and_wakeup(unsigned long tmp)
238 {
239 if (caa_likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
240 smp_mb_slave();
241 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp - RCU_GP_COUNT);
242 smp_mb_slave();
243 wake_up_gp();
244 } else
245 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp - RCU_GP_COUNT);
246 }
247
248 /*
249 * Exit an RCU read-side crtical section. Both this function and its
250 * helper are smaller than 10 lines of code, and are intended to be
251 * usable by non-LGPL code, as called out in LGPL.
252 */
253 static inline void _rcu_read_unlock(void)
254 {
255 unsigned long tmp;
256
257 urcu_assert(URCU_TLS(rcu_reader).registered);
258 tmp = URCU_TLS(rcu_reader).ctr;
259 urcu_assert(tmp & RCU_GP_CTR_NEST_MASK);
260 _rcu_read_unlock_update_and_wakeup(tmp);
261 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
262 }
263
264 /*
265 * Returns whether within a RCU read-side critical section.
266 *
267 * This function is less than 10 lines long. The intent is that this
268 * function meets the 10-line criterion for LGPL, allowing this function
269 * to be invoked directly from non-LGPL code.
270 */
271 static inline int _rcu_read_ongoing(void)
272 {
273 return URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK;
274 }
275
276 #ifdef __cplusplus
277 }
278 #endif
279
280 #endif /* _URCU_STATIC_H */
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