Add rcu_read_ongoing() API to each urcu flavor
[urcu.git] / urcu / static / urcu-bp.h
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
52 extern "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
61 enum 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
83 extern unsigned int rcu_yield_active;
84 extern DECLARE_URCU_TLS(unsigned int, rcu_rand_yield);
85
86 static 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
93 static 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
100 static inline void rcu_debug_yield_init(void)
101 {
102 URCU_TLS(rcu_rand_yield) = time(NULL) ^ (unsigned long) pthread_self();
103 }
104 #else
105 static inline void rcu_debug_yield_read(void)
106 {
107 }
108
109 static inline void rcu_debug_yield_write(void)
110 {
111 }
112
113 static 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 */
131 extern void rcu_bp_register(void);
132
133 /*
134 * Global quiescent period counter with low-order bits unused.
135 * Using a int rather than a char to eliminate false register dependencies
136 * causing stalls on some architectures.
137 */
138 extern unsigned long rcu_gp_ctr;
139
140 struct rcu_reader {
141 /* Data used by both reader and synchronize_rcu() */
142 unsigned long ctr;
143 /* Data used for registry */
144 struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
145 pthread_t tid;
146 int alloc; /* registry entry allocated */
147 };
148
149 /*
150 * Bulletproof version keeps a pointer to a registry not part of the TLS.
151 * Adds a pointer dereference on the read-side, but won't require to unregister
152 * the reader thread.
153 */
154 extern DECLARE_URCU_TLS(struct rcu_reader *, rcu_reader);
155
156 static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
157 {
158 unsigned long v;
159
160 if (ctr == NULL)
161 return RCU_READER_INACTIVE;
162 /*
163 * Make sure both tests below are done on the same version of *value
164 * to insure consistency.
165 */
166 v = CMM_LOAD_SHARED(*ctr);
167 if (!(v & RCU_GP_CTR_NEST_MASK))
168 return RCU_READER_INACTIVE;
169 if (!((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE))
170 return RCU_READER_ACTIVE_CURRENT;
171 return RCU_READER_ACTIVE_OLD;
172 }
173
174 /*
175 * Helper for _rcu_read_lock(). The format of rcu_gp_ctr (as well as
176 * the per-thread rcu_reader.ctr) has the upper bits containing a count of
177 * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
178 * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in
179 * _rcu_read_lock() happen before the subsequent read-side critical section.
180 */
181 static inline void _rcu_read_lock_update(unsigned long tmp)
182 {
183 if (caa_likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
184 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, _CMM_LOAD_SHARED(rcu_gp_ctr));
185 cmm_smp_mb();
186 } else
187 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, tmp + RCU_GP_COUNT);
188 }
189
190 /*
191 * Enter an RCU read-side critical section.
192 *
193 * The first cmm_barrier() call ensures that the compiler does not reorder
194 * the body of _rcu_read_lock() with a mutex.
195 *
196 * This function and its helper are both less than 10 lines long. The
197 * intent is that this function meets the 10-line criterion in LGPL,
198 * allowing this function to be invoked directly from non-LGPL code.
199 */
200 static inline void _rcu_read_lock(void)
201 {
202 unsigned long tmp;
203
204 if (caa_unlikely(!URCU_TLS(rcu_reader)))
205 rcu_bp_register(); /* If not yet registered. */
206 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
207 tmp = URCU_TLS(rcu_reader)->ctr;
208 _rcu_read_lock_update(tmp);
209 }
210
211 /*
212 * Exit an RCU read-side critical section. This function is less than
213 * 10 lines of code, and is intended to be usable by non-LGPL code, as
214 * called out in LGPL.
215 */
216 static inline void _rcu_read_unlock(void)
217 {
218 /*
219 * Finish using rcu before decrementing the pointer.
220 */
221 cmm_smp_mb();
222 _CMM_STORE_SHARED(URCU_TLS(rcu_reader)->ctr, URCU_TLS(rcu_reader)->ctr - RCU_GP_COUNT);
223 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
224 }
225
226 /*
227 * Returns whether within a RCU read-side critical section.
228 *
229 * This function is less than 10 lines long. The intent is that this
230 * function meets the 10-line criterion for LGPL, allowing this function
231 * to be invoked directly from non-LGPL code.
232 */
233 static inline int _rcu_read_ongoing(void)
234 {
235 if (caa_unlikely(!URCU_TLS(rcu_reader)))
236 rcu_bp_register(); /* If not yet registered. */
237 return URCU_TLS(rcu_reader)->ctr & RCU_GP_CTR_NEST_MASK;
238 }
239
240 #ifdef __cplusplus
241 }
242 #endif
243
244 #endif /* _URCU_BP_STATIC_H */
This page took 0.056811 seconds and 4 git commands to generate.