add missing comment to wfstack.c
[urcu.git] / urcu-bp-static.h
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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 *
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 <syscall.h>
35#include <unistd.h>
36
37#include <urcu/compiler.h>
38#include <urcu/arch.h>
39#include <urcu/system.h>
48d848c7 40#include <urcu/uatomic_arch.h>
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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
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51#ifdef __cplusplus
52extern "C" {
53#endif
54
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55/*
56 * Active attempts to check for reader Q.S. before calling sleep().
57 */
58#define RCU_QS_ACTIVE_ATTEMPTS 100
59
60#ifdef DEBUG_RCU
61#define rcu_assert(args...) assert(args)
62#else
63#define rcu_assert(args...)
64#endif
65
66#ifdef DEBUG_YIELD
67#include <sched.h>
68#include <time.h>
69#include <pthread.h>
70#include <unistd.h>
71
72#define YIELD_READ (1 << 0)
73#define YIELD_WRITE (1 << 1)
74
75/*
02be5561 76 * Updates without RCU_MB are much slower. Account this in
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77 * the delay.
78 */
79/* maximum sleep delay, in us */
80#define MAX_SLEEP 50
81
82extern unsigned int yield_active;
83extern unsigned int __thread rand_yield;
84
85static inline void debug_yield_read(void)
86{
87 if (yield_active & YIELD_READ)
88 if (rand_r(&rand_yield) & 0x1)
89 usleep(rand_r(&rand_yield) % MAX_SLEEP);
90}
91
92static inline void debug_yield_write(void)
93{
94 if (yield_active & YIELD_WRITE)
95 if (rand_r(&rand_yield) & 0x1)
96 usleep(rand_r(&rand_yield) % MAX_SLEEP);
97}
98
99static inline void debug_yield_init(void)
100{
101 rand_yield = time(NULL) ^ pthread_self();
102}
103#else
104static inline void debug_yield_read(void)
105{
106}
107
108static inline void debug_yield_write(void)
109{
110}
111
112static inline void debug_yield_init(void)
113{
114
115}
116#endif
117
118/*
02be5561 119 * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use a
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120 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
121 */
122#define RCU_GP_COUNT (1UL << 0)
123/* Use the amount of bits equal to half of the architecture long size */
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124#define RCU_GP_CTR_PHASE (1UL << (sizeof(long) << 2))
125#define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_PHASE - 1)
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126
127/*
128 * Used internally by _rcu_read_lock.
129 */
130extern void rcu_bp_register(void);
131
132/*
133 * Global quiescent period counter with low-order bits unused.
134 * Using a int rather than a char to eliminate false register dependencies
135 * causing stalls on some architectures.
136 */
02be5561 137extern long rcu_gp_ctr;
fdee2e6d 138
02be5561 139struct rcu_reader {
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140 /* Data used by both reader and synchronize_rcu() */
141 long ctr;
142 /* Data used for registry */
18c3778a 143 struct list_head node __attribute__((aligned(CACHE_LINE_SIZE)));
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144 pthread_t tid;
145 int alloc; /* registry entry allocated */
146};
147
148/*
149 * Bulletproof version keeps a pointer to a registry not part of the TLS.
150 * Adds a pointer dereference on the read-side, but won't require to unregister
151 * the reader thread.
152 */
02be5561 153extern struct rcu_reader __thread *rcu_reader;
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154
155static inline int rcu_old_gp_ongoing(long *value)
156{
157 long v;
158
159 if (value == NULL)
160 return 0;
161 /*
162 * Make sure both tests below are done on the same version of *value
163 * to insure consistency.
164 */
165 v = LOAD_SHARED(*value);
166 return (v & RCU_GP_CTR_NEST_MASK) &&
02be5561 167 ((v ^ rcu_gp_ctr) & RCU_GP_CTR_PHASE);
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168}
169
170static inline void _rcu_read_lock(void)
171{
172 long tmp;
173
174 /* Check if registered */
02be5561 175 if (unlikely(!rcu_reader))
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176 rcu_bp_register();
177
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178 tmp = rcu_reader->ctr;
179 /*
180 * rcu_gp_ctr is
181 * RCU_GP_COUNT | (~RCU_GP_CTR_PHASE or RCU_GP_CTR_PHASE)
182 */
fdee2e6d 183 if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
02be5561 184 _STORE_SHARED(rcu_reader->ctr, _LOAD_SHARED(rcu_gp_ctr));
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185 /*
186 * Set active readers count for outermost nesting level before
187 * accessing the pointer.
188 */
189 smp_mb();
190 } else {
02be5561 191 _STORE_SHARED(rcu_reader->ctr, tmp + RCU_GP_COUNT);
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192 }
193}
194
195static inline void _rcu_read_unlock(void)
196{
197 /*
198 * Finish using rcu before decrementing the pointer.
199 */
200 smp_mb();
02be5561 201 _STORE_SHARED(rcu_reader->ctr, rcu_reader->ctr - RCU_GP_COUNT);
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202}
203
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204#ifdef __cplusplus
205}
206#endif
207
fdee2e6d 208#endif /* _URCU_BP_STATIC_H */
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