3fb457b4e3e00916b2a2e06e172b4eced08f0df0
[urcu.git] / 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/compiler.h>
38 #include <urcu/arch.h>
39 #include <urcu/system.h>
40 #include <urcu/uatomic.h>
41 #include <urcu/list.h>
42 #include <urcu/futex.h>
43 #include <urcu/tls-compat.h>
44 #include <urcu/rand-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 * RCU memory barrier broadcast group. Currently, only broadcast to all process
85 * threads is supported (group 0).
86 *
87 * Slave barriers are only guaranteed to be ordered wrt master barriers.
88 *
89 * The pair ordering is detailed as (O: ordered, X: not ordered) :
90 * slave master
91 * slave X O
92 * master O O
93 */
94
95 #define MB_GROUP_ALL 0
96 #define RCU_MB_GROUP MB_GROUP_ALL
97
98 #ifdef RCU_MEMBARRIER
99 extern int rcu_has_sys_membarrier;
100
101 static inline void smp_mb_slave(int group)
102 {
103 if (caa_likely(rcu_has_sys_membarrier))
104 cmm_barrier();
105 else
106 cmm_smp_mb();
107 }
108 #endif
109
110 #ifdef RCU_MB
111 static inline void smp_mb_slave(int group)
112 {
113 cmm_smp_mb();
114 }
115 #endif
116
117 #ifdef RCU_SIGNAL
118 static inline void smp_mb_slave(int group)
119 {
120 cmm_barrier();
121 }
122 #endif
123
124 /*
125 * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use
126 * a full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
127 */
128 #define RCU_GP_COUNT (1UL << 0)
129 /* Use the amount of bits equal to half of the architecture long size */
130 #define RCU_GP_CTR_PHASE (1UL << (sizeof(unsigned long) << 2))
131 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_PHASE - 1)
132
133 struct rcu_gp {
134 /*
135 * Global grace period counter.
136 * Contains the current RCU_GP_CTR_PHASE.
137 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
138 * Written to only by writer with mutex taken.
139 * Read by both writer and readers.
140 */
141 unsigned long ctr;
142
143 int32_t futex;
144 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
145
146 extern struct rcu_gp rcu_gp;
147
148 struct rcu_reader {
149 /* Data used by both reader and synchronize_rcu() */
150 unsigned long ctr;
151 char need_mb;
152 /* Data used for registry */
153 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
154 pthread_t tid;
155 /* Reader registered flag, for internal checks. */
156 unsigned int registered:1;
157 };
158
159 extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
160
161 /*
162 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
163 */
164 static inline void wake_up_gp(void)
165 {
166 if (caa_unlikely(uatomic_read(&rcu_gp.futex) == -1)) {
167 uatomic_set(&rcu_gp.futex, 0);
168 /*
169 * Ignoring return value until we can make this function
170 * return something (because urcu_die() is not publicly
171 * exposed).
172 */
173 (void) futex_async(&rcu_gp.futex, FUTEX_WAKE, 1,
174 NULL, NULL, 0);
175 }
176 }
177
178 static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
179 {
180 unsigned long v;
181
182 /*
183 * Make sure both tests below are done on the same version of *value
184 * to insure consistency.
185 */
186 v = CMM_LOAD_SHARED(*ctr);
187 if (!(v & RCU_GP_CTR_NEST_MASK))
188 return RCU_READER_INACTIVE;
189 if (!((v ^ rcu_gp.ctr) & RCU_GP_CTR_PHASE))
190 return RCU_READER_ACTIVE_CURRENT;
191 return RCU_READER_ACTIVE_OLD;
192 }
193
194 /*
195 * Helper for _rcu_read_lock(). The format of rcu_gp.ctr (as well as
196 * the per-thread rcu_reader.ctr) has the upper bits containing a count of
197 * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
198 * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in
199 * _rcu_read_lock() happen before the subsequent read-side critical section.
200 */
201 static inline void _rcu_read_lock_update(unsigned long tmp)
202 {
203 if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
204 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, _CMM_LOAD_SHARED(rcu_gp.ctr));
205 smp_mb_slave(RCU_MB_GROUP);
206 } else
207 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp + RCU_GP_COUNT);
208 }
209
210 /*
211 * Enter an RCU read-side critical section.
212 *
213 * The first cmm_barrier() call ensures that the compiler does not reorder
214 * the body of _rcu_read_lock() with a mutex.
215 *
216 * This function and its helper are both less than 10 lines long. The
217 * intent is that this function meets the 10-line criterion in LGPL,
218 * allowing this function to be invoked directly from non-LGPL code.
219 */
220 static inline void _rcu_read_lock(void)
221 {
222 unsigned long tmp;
223
224 urcu_assert(URCU_TLS(rcu_reader).registered);
225 cmm_barrier();
226 tmp = URCU_TLS(rcu_reader).ctr;
227 urcu_assert((tmp & RCU_GP_CTR_NEST_MASK) != RCU_GP_CTR_NEST_MASK);
228 _rcu_read_lock_update(tmp);
229 }
230
231 /*
232 * This is a helper function for _rcu_read_unlock().
233 *
234 * The first smp_mb_slave() call ensures that the critical section is
235 * seen to precede the store to rcu_reader.ctr.
236 * The second smp_mb_slave() call ensures that we write to rcu_reader.ctr
237 * before reading the update-side futex.
238 */
239 static inline void _rcu_read_unlock_update_and_wakeup(unsigned long tmp)
240 {
241 if (caa_likely((tmp & RCU_GP_CTR_NEST_MASK) == RCU_GP_COUNT)) {
242 smp_mb_slave(RCU_MB_GROUP);
243 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp - RCU_GP_COUNT);
244 smp_mb_slave(RCU_MB_GROUP);
245 wake_up_gp();
246 } else
247 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, tmp - RCU_GP_COUNT);
248 }
249
250 /*
251 * Exit an RCU read-side crtical section. Both this function and its
252 * helper are smaller than 10 lines of code, and are intended to be
253 * usable by non-LGPL code, as called out in LGPL.
254 */
255 static inline void _rcu_read_unlock(void)
256 {
257 unsigned long tmp;
258
259 urcu_assert(URCU_TLS(rcu_reader).registered);
260 tmp = URCU_TLS(rcu_reader).ctr;
261 urcu_assert(tmp & RCU_GP_CTR_NEST_MASK);
262 _rcu_read_unlock_update_and_wakeup(tmp);
263 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
264 }
265
266 /*
267 * Returns whether within a RCU read-side critical section.
268 *
269 * This function is less than 10 lines long. The intent is that this
270 * function meets the 10-line criterion for LGPL, allowing this function
271 * to be invoked directly from non-LGPL code.
272 */
273 static inline int _rcu_read_ongoing(void)
274 {
275 return URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK;
276 }
277
278 #ifdef __cplusplus
279 }
280 #endif
281
282 #endif /* _URCU_STATIC_H */
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