urcu-bp: introduce struct urcu_gp
[urcu.git] / urcu / static / urcu-bp.h
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CommitLineData
1#ifndef _URCU_BP_STATIC_H
2#define _URCU_BP_STATIC_H
3
4/*
5 * urcu-bp-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
36#include <urcu/compiler.h>
37#include <urcu/arch.h>
38#include <urcu/system.h>
39#include <urcu/uatomic.h>
40#include <urcu/list.h>
41#include <urcu/tls-compat.h>
42
43/*
44 * This code section can only be included in LGPL 2.1 compatible source code.
45 * See below for the function call wrappers which can be used in code meant to
46 * be only linked with the Userspace RCU library. This comes with a small
47 * performance degradation on the read-side due to the added function calls.
48 * This is required to permit relinking with newer versions of the library.
49 */
50
51#ifdef __cplusplus
52extern "C" {
53#endif
54
55#ifdef DEBUG_RCU
56#define rcu_assert(args...) assert(args)
57#else
58#define rcu_assert(args...)
59#endif
60
61enum rcu_state {
62 RCU_READER_ACTIVE_CURRENT,
63 RCU_READER_ACTIVE_OLD,
64 RCU_READER_INACTIVE,
65};
66
67#ifdef DEBUG_YIELD
68#include <sched.h>
69#include <time.h>
70#include <pthread.h>
71#include <unistd.h>
72
73#define RCU_YIELD_READ (1 << 0)
74#define RCU_YIELD_WRITE (1 << 1)
75
76/*
77 * Updates without RCU_MB are much slower. Account this in
78 * the delay.
79 */
80/* maximum sleep delay, in us */
81#define MAX_SLEEP 50
82
83extern unsigned int rcu_yield_active;
84extern DECLARE_URCU_TLS(unsigned int, rcu_rand_yield);
85
86static inline void rcu_debug_yield_read(void)
87{
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);
91}
92
93static inline void rcu_debug_yield_write(void)
94{
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);
98}
99
100static inline void rcu_debug_yield_init(void)
101{
102 URCU_TLS(rcu_rand_yield) = time(NULL) ^ (unsigned long) pthread_self();
103}
104#else
105static inline void rcu_debug_yield_read(void)
106{
107}
108
109static inline void rcu_debug_yield_write(void)
110{
111}
112
113static inline void rcu_debug_yield_init(void)
114{
115
116}
117#endif
118
119/*
120 * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use a
121 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
122 */
123#define RCU_GP_COUNT (1UL << 0)
124/* Use the amount of bits equal to half of the architecture long size */
125#define RCU_GP_CTR_PHASE (1UL << (sizeof(long) << 2))
126#define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_PHASE - 1)
127
128/*
129 * Used internally by _rcu_read_lock.
130 */
131extern void rcu_bp_register(void);
132
133struct 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} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
143
144extern struct rcu_gp rcu_gp;
145
146struct rcu_reader {
147 /* Data used by both reader and synchronize_rcu() */
148 unsigned long ctr;
149 /* Data used for registry */
150 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
151 pthread_t tid;
152 int alloc; /* registry entry allocated */
153};
154
155/*
156 * Bulletproof version keeps a pointer to a registry not part of the TLS.
157 * Adds a pointer dereference on the read-side, but won't require to unregister
158 * the reader thread.
159 */
160extern DECLARE_URCU_TLS(struct rcu_reader *, rcu_reader);
161
162static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
163{
164 unsigned long v;
165
166 if (ctr == NULL)
167 return RCU_READER_INACTIVE;
168 /*
169 * Make sure both tests below are done on the same version of *value
170 * to insure consistency.
171 */
172 v = CMM_LOAD_SHARED(*ctr);
173 if (!(v & RCU_GP_CTR_NEST_MASK))
174 return RCU_READER_INACTIVE;
175 if (!((v ^ rcu_gp.ctr) & RCU_GP_CTR_PHASE))
176 return RCU_READER_ACTIVE_CURRENT;
177 return RCU_READER_ACTIVE_OLD;
178}
179
180/*
181 * Helper for _rcu_read_lock(). The format of rcu_gp.ctr (as well as
182 * the per-thread rcu_reader.ctr) has the upper bits containing a count of
183 * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
184 * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in
185 * _rcu_read_lock() happen before the subsequent read-side critical section.
186 */
187static inline void _rcu_read_lock_update(unsigned long tmp)
188{
189 if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
190 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, _CMM_LOAD_SHARED(rcu_gp.ctr));
191 cmm_smp_mb();
192 } else
193 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, tmp + RCU_GP_COUNT);
194}
195
196/*
197 * Enter an RCU read-side critical section.
198 *
199 * The first cmm_barrier() call ensures that the compiler does not reorder
200 * the body of _rcu_read_lock() with a mutex.
201 *
202 * This function and its helper are both less than 10 lines long. The
203 * intent is that this function meets the 10-line criterion in LGPL,
204 * allowing this function to be invoked directly from non-LGPL code.
205 */
206static inline void _rcu_read_lock(void)
207{
208 unsigned long tmp;
209
210 if (caa_unlikely(!URCU_TLS(rcu_reader)))
211 rcu_bp_register(); /* If not yet registered. */
212 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
213 tmp = URCU_TLS(rcu_reader)->ctr;
214 _rcu_read_lock_update(tmp);
215}
216
217/*
218 * Exit an RCU read-side critical section. This function is less than
219 * 10 lines of code, and is intended to be usable by non-LGPL code, as
220 * called out in LGPL.
221 */
222static inline void _rcu_read_unlock(void)
223{
224 /*
225 * Finish using rcu before decrementing the pointer.
226 */
227 cmm_smp_mb();
228 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, URCU_TLS(rcu_reader)->ctr - RCU_GP_COUNT);
229 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
230}
231
232/*
233 * Returns whether within a RCU read-side critical section.
234 *
235 * This function is less than 10 lines long. The intent is that this
236 * function meets the 10-line criterion for LGPL, allowing this function
237 * to be invoked directly from non-LGPL code.
238 */
239static inline int _rcu_read_ongoing(void)
240{
241 if (caa_unlikely(!URCU_TLS(rcu_reader)))
242 rcu_bp_register(); /* If not yet registered. */
243 return URCU_TLS(rcu_reader)->ctr & RCU_GP_CTR_NEST_MASK;
244}
245
246#ifdef __cplusplus
247}
248#endif
249
250#endif /* _URCU_BP_STATIC_H */
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