Add rcu_read_ongoing() API to each urcu flavor
[urcu.git] / urcu / static / urcu-qsbr.h
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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 *
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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.
7ac06cef 11 *
6982d6d7 12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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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 <assert.h>
f0f7dbdd 35#include <limits.h>
bc6c15bb 36#include <unistd.h>
6d841bc2 37#include <stdint.h>
7ac06cef 38
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39#include <urcu/compiler.h>
40#include <urcu/arch.h>
7e30abe3 41#include <urcu/system.h>
a2e7bf9c 42#include <urcu/uatomic.h>
4f8e3380 43#include <urcu/list.h>
41849996 44#include <urcu/futex.h>
bd252a04 45#include <urcu/tls-compat.h>
bc6c15bb 46
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47#ifdef __cplusplus
48extern "C" {
49#endif
50
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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
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59#ifdef DEBUG_RCU
60#define rcu_assert(args...) assert(args)
61#else
62#define rcu_assert(args...)
63#endif
64
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65enum rcu_state {
66 RCU_READER_ACTIVE_CURRENT,
67 RCU_READER_ACTIVE_OLD,
68 RCU_READER_INACTIVE,
69};
70
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71#ifdef DEBUG_YIELD
72#include <sched.h>
73#include <time.h>
74#include <pthread.h>
75#include <unistd.h>
76
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77#define RCU_YIELD_READ (1 << 0)
78#define RCU_YIELD_WRITE (1 << 1)
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79
80/* maximum sleep delay, in us */
81#define MAX_SLEEP 50
82
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83extern unsigned int rcu_yield_active;
84extern DECLARE_URCU_TLS(unsigned int, rcu_rand_yield);
7ac06cef 85
1de4df4b 86static inline void rcu_debug_yield_read(void)
7ac06cef 87{
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88 if (rcu_yield_active & RCU_YIELD_READ)
89 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
90 usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
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91}
92
1de4df4b 93static inline void rcu_debug_yield_write(void)
7ac06cef 94{
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95 if (rcu_yield_active & RCU_YIELD_WRITE)
96 if (rand_r(&URCU_TLS(rcu_rand_yield)) & 0x1)
97 usleep(rand_r(&URCU_TLS(rcu_rand_yield)) % MAX_SLEEP);
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98}
99
1de4df4b 100static inline void rcu_debug_yield_init(void)
7ac06cef 101{
6ff854ac 102 URCU_TLS(rcu_rand_yield) = time(NULL) ^ (unsigned long) pthread_self();
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103}
104#else
1de4df4b 105static inline void rcu_debug_yield_read(void)
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106{
107}
108
1de4df4b 109static inline void rcu_debug_yield_write(void)
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110{
111}
112
1de4df4b 113static inline void rcu_debug_yield_init(void)
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114{
115
116}
117#endif
118
ac258107 119#define RCU_GP_ONLINE (1UL << 0)
55570466 120#define RCU_GP_CTR (1UL << 1)
ac258107 121
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122/*
123 * Global quiescent period counter with low-order bits unused.
124 * Using a int rather than a char to eliminate false register dependencies
125 * causing stalls on some architectures.
126 */
02be5561 127extern unsigned long rcu_gp_ctr;
7ac06cef 128
02be5561 129struct rcu_reader {
bd1a5e15 130 /* Data used by both reader and synchronize_rcu() */
4f8e3380 131 unsigned long ctr;
bd1a5e15 132 /* Data used for registry */
16aa9ee8 133 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
83a2c421 134 int waiting;
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135 pthread_t tid;
136};
137
bd252a04 138extern DECLARE_URCU_TLS(struct rcu_reader, rcu_reader);
7ac06cef 139
1de4df4b 140extern int32_t rcu_gp_futex;
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141
142/*
143 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
144 */
145static inline void wake_up_gp(void)
146{
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147 if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(rcu_reader).waiting))) {
148 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).waiting, 0);
83a2c421 149 cmm_smp_mb();
1de4df4b 150 if (uatomic_read(&rcu_gp_futex) != -1)
83a2c421 151 return;
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152 uatomic_set(&rcu_gp_futex, 0);
153 futex_noasync(&rcu_gp_futex, FUTEX_WAKE, 1,
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154 NULL, NULL, 0);
155 }
156}
157
708d89f0 158static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
7ac06cef 159{
e26fa029 160 unsigned long v;
4e560c17 161
6cf3827c 162 v = CMM_LOAD_SHARED(*ctr);
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163 if (!v)
164 return RCU_READER_INACTIVE;
165 if (v == rcu_gp_ctr)
166 return RCU_READER_ACTIVE_CURRENT;
167 return RCU_READER_ACTIVE_OLD;
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168}
169
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170/*
171 * Enter an RCU read-side critical section.
172 *
173 * This function is less than 10 lines long. The intent is that this
174 * function meets the 10-line criterion for LGPL, allowing this function
175 * to be invoked directly from non-LGPL code.
176 */
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177static inline void _rcu_read_lock(void)
178{
bd252a04 179 rcu_assert(URCU_TLS(rcu_reader).ctr);
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180}
181
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182/*
183 * Exit an RCU read-side critical section.
184 *
185 * This function is less than 10 lines long. The intent is that this
186 * function meets the 10-line criterion for LGPL, allowing this function
187 * to be invoked directly from non-LGPL code.
188 */
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189static inline void _rcu_read_unlock(void)
190{
191}
192
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193/*
194 * Returns whether within a RCU read-side critical section.
195 *
196 * This function is less than 10 lines long. The intent is that this
197 * function meets the 10-line criterion for LGPL, allowing this function
198 * to be invoked directly from non-LGPL code.
199 */
200static inline int _rcu_read_ongoing(void)
201{
202 return URCU_TLS(rcu_reader).ctr;
203}
204
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205/*
206 * This is a helper function for _rcu_quiescent_state().
207 * The first cmm_smp_mb() ensures memory accesses in the prior read-side
208 * critical sections are not reordered with store to
209 * URCU_TLS(rcu_reader).ctr, and ensures that mutexes held within an
210 * offline section that would happen to end with this
211 * rcu_quiescent_state() call are not reordered with
212 * store to URCU_TLS(rcu_reader).ctr.
213 */
214static inline void _rcu_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
215{
216 cmm_smp_mb();
217 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, gp_ctr);
218 cmm_smp_mb(); /* write URCU_TLS(rcu_reader).ctr before read futex */
219 wake_up_gp();
220 cmm_smp_mb();
221}
222
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223/*
224 * Inform RCU of a quiescent state.
225 *
226 * This function is less than 10 lines long. The intent is that this
227 * function meets the 10-line criterion for LGPL, allowing this function
228 * to be invoked directly from non-LGPL code.
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229 *
230 * We skip the memory barriers and gp store if our local ctr already
231 * matches the global rcu_gp_ctr value: this is OK because a prior
232 * _rcu_quiescent_state() or _rcu_thread_online() already updated it
233 * within our thread, so we have no quiescent state to report.
a5a9f428 234 */
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235static inline void _rcu_quiescent_state(void)
236{
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237 unsigned long gp_ctr;
238
239 if ((gp_ctr = CMM_LOAD_SHARED(rcu_gp_ctr)) == URCU_TLS(rcu_reader).ctr)
240 return;
241 _rcu_quiescent_state_update_and_wakeup(gp_ctr);
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242}
243
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244/*
245 * Take a thread offline, prohibiting it from entering further RCU
246 * read-side critical sections.
247 *
248 * This function is less than 10 lines long. The intent is that this
249 * function meets the 10-line criterion for LGPL, allowing this function
250 * to be invoked directly from non-LGPL code.
251 */
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252static inline void _rcu_thread_offline(void)
253{
5481ddb3 254 cmm_smp_mb();
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255 CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, 0);
256 cmm_smp_mb(); /* write URCU_TLS(rcu_reader).ctr before read futex */
bc6c15bb 257 wake_up_gp();
5481ddb3 258 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
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259}
260
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261/*
262 * Bring a thread online, allowing it to once again enter RCU
263 * read-side critical sections.
264 *
265 * This function is less than 10 lines long. The intent is that this
266 * function meets the 10-line criterion for LGPL, allowing this function
267 * to be invoked directly from non-LGPL code.
268 */
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269static inline void _rcu_thread_online(void)
270{
5481ddb3 271 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
bd252a04 272 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, CMM_LOAD_SHARED(rcu_gp_ctr));
5481ddb3 273 cmm_smp_mb();
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274}
275
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276#ifdef __cplusplus
277}
278#endif
279
7ac06cef 280#endif /* _URCU_QSBR_STATIC_H */
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