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[urcu.git] / urcu-bp-static.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 LGPL-COMPATIBLE CODE. See urcu.h for linking
10 * dynamically with the userspace rcu library.
11 *
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
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 <syscall.h>
35 #include <unistd.h>
36
37 #include <urcu/compiler.h>
38 #include <urcu/arch.h>
39 #include <urcu/system.h>
40 #include <urcu/uatomic_arch.h>
41 #include <urcu/list.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 /*
52 * Active attempts to check for reader Q.S. before calling sleep().
53 */
54 #define RCU_QS_ACTIVE_ATTEMPTS 100
55
56 #ifdef DEBUG_RCU
57 #define rcu_assert(args...) assert(args)
58 #else
59 #define rcu_assert(args...)
60 #endif
61
62 #ifdef DEBUG_YIELD
63 #include <sched.h>
64 #include <time.h>
65 #include <pthread.h>
66 #include <unistd.h>
67
68 #define YIELD_READ (1 << 0)
69 #define YIELD_WRITE (1 << 1)
70
71 /*
72 * Updates without URCU_MB are much slower. Account this in
73 * the delay.
74 */
75 /* maximum sleep delay, in us */
76 #define MAX_SLEEP 50
77
78 extern unsigned int yield_active;
79 extern unsigned int __thread rand_yield;
80
81 static inline void debug_yield_read(void)
82 {
83 if (yield_active & YIELD_READ)
84 if (rand_r(&rand_yield) & 0x1)
85 usleep(rand_r(&rand_yield) % MAX_SLEEP);
86 }
87
88 static inline void debug_yield_write(void)
89 {
90 if (yield_active & YIELD_WRITE)
91 if (rand_r(&rand_yield) & 0x1)
92 usleep(rand_r(&rand_yield) % MAX_SLEEP);
93 }
94
95 static inline void debug_yield_init(void)
96 {
97 rand_yield = time(NULL) ^ pthread_self();
98 }
99 #else
100 static inline void debug_yield_read(void)
101 {
102 }
103
104 static inline void debug_yield_write(void)
105 {
106 }
107
108 static inline void debug_yield_init(void)
109 {
110
111 }
112 #endif
113
114 /*
115 * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
116 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
117 */
118 #define RCU_GP_COUNT (1UL << 0)
119 /* Use the amount of bits equal to half of the architecture long size */
120 #define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
121 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
122
123 /*
124 * Used internally by _rcu_read_lock.
125 */
126 extern void rcu_bp_register(void);
127
128 /*
129 * Global quiescent period counter with low-order bits unused.
130 * Using a int rather than a char to eliminate false register dependencies
131 * causing stalls on some architectures.
132 */
133 extern long urcu_gp_ctr;
134
135 struct urcu_reader {
136 /* Data used by both reader and synchronize_rcu() */
137 long ctr;
138 /* Data used for registry */
139 struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
140 pthread_t tid;
141 int alloc; /* registry entry allocated */
142 };
143
144 /*
145 * Bulletproof version keeps a pointer to a registry not part of the TLS.
146 * Adds a pointer dereference on the read-side, but won't require to unregister
147 * the reader thread.
148 */
149 extern struct urcu_reader __thread *urcu_reader;
150
151 static inline int rcu_old_gp_ongoing(long *value)
152 {
153 long v;
154
155 if (value == NULL)
156 return 0;
157 /*
158 * Make sure both tests below are done on the same version of *value
159 * to insure consistency.
160 */
161 v = LOAD_SHARED(*value);
162 return (v & RCU_GP_CTR_NEST_MASK) &&
163 ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
164 }
165
166 static inline void _rcu_read_lock(void)
167 {
168 long tmp;
169
170 /* Check if registered */
171 if (unlikely(!urcu_reader))
172 rcu_bp_register();
173
174 tmp = urcu_reader->ctr;
175 /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
176 if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
177 _STORE_SHARED(urcu_reader->ctr, _LOAD_SHARED(urcu_gp_ctr));
178 /*
179 * Set active readers count for outermost nesting level before
180 * accessing the pointer.
181 */
182 smp_mb();
183 } else {
184 _STORE_SHARED(urcu_reader->ctr, tmp + RCU_GP_COUNT);
185 }
186 }
187
188 static inline void _rcu_read_unlock(void)
189 {
190 /*
191 * Finish using rcu before decrementing the pointer.
192 */
193 smp_mb();
194 _STORE_SHARED(urcu_reader->ctr, urcu_reader->ctr - RCU_GP_COUNT);
195 }
196
197 #endif /* _URCU_BP_STATIC_H */
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