Add randomness to yield debug test
[urcu.git] / urcu.h
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1#ifndef _URCU_H
2#define _URCU_H
3
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4/*
5 * urcu.h
6 *
7 * Userspace RCU header
8 *
9 * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
10 *
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11 * Credits for Paul e. McKenney <paulmck@linux.vnet.ibm.com>
12 * for inspiration coming from the Linux kernel RCU and rcu-preempt.
13 *
14 * The barrier, mb, rmb, wmb, atomic_inc, smp_read_barrier_depends, ACCESS_ONCE
15 * and rcu_dereference primitives come from the Linux kernel.
16 *
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17 * Distributed under GPLv2
18 */
19
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20/* The "volatile" is due to gcc bugs */
21#define barrier() __asm__ __volatile__("": : :"memory")
22
23/* x86 32/64 specific */
24#define mb() asm volatile("mfence":::"memory")
25#define rmb() asm volatile("lfence":::"memory")
26#define wmb() asm volatile("sfence" ::: "memory")
27
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28static inline void atomic_inc(int *v)
29{
30 asm volatile("lock; incl %0"
f69f195a 31 : "+m" (*v));
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32}
33
34/* Nop everywhere except on alpha. */
35#define smp_read_barrier_depends()
36
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37/*
38 * Prevent the compiler from merging or refetching accesses. The compiler
39 * is also forbidden from reordering successive instances of ACCESS_ONCE(),
40 * but only when the compiler is aware of some particular ordering. One way
41 * to make the compiler aware of ordering is to put the two invocations of
42 * ACCESS_ONCE() in different C statements.
43 *
44 * This macro does absolutely -nothing- to prevent the CPU from reordering,
45 * merging, or refetching absolutely anything at any time. Its main intended
46 * use is to mediate communication between process-level code and irq/NMI
47 * handlers, all running on the same CPU.
48 */
49#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
50
51/**
52 * rcu_dereference - fetch an RCU-protected pointer in an
53 * RCU read-side critical section. This pointer may later
54 * be safely dereferenced.
55 *
56 * Inserts memory barriers on architectures that require them
57 * (currently only the Alpha), and, more importantly, documents
58 * exactly which pointers are protected by RCU.
59 */
60
61#define rcu_dereference(p) ({ \
62 typeof(p) _________p1 = ACCESS_ONCE(p); \
63 smp_read_barrier_depends(); \
64 (_________p1); \
65 })
66
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67#define SIGURCU SIGUSR1
68
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69#ifdef DEBUG_YIELD
70#include <sched.h>
71
72#define YIELD_READ (1 << 0)
73#define YIELD_WRITE (1 << 1)
74
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75extern unsigned int yield_active;
76extern unsigned int __thread rand_yield;
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77
78static inline void debug_yield_read(void)
79{
80 if (yield_active & YIELD_READ)
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81 if (rand_r(&rand_yield) & 0x1)
82 sched_yield();
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83}
84
85static inline void debug_yield_write(void)
86{
87 if (yield_active & YIELD_WRITE)
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88 if (rand_r(&rand_yield) & 0x1)
89 sched_yield();
90}
91
92static inline void debug_yield_init(void)
93{
94 rand_yield = time(NULL) ^ pthread_self();
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95}
96#else
97static inline void debug_yield_read(void)
98{
99}
100
101static inline void debug_yield_write(void)
102{
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103}
104
105static inline void debug_yield_init(void)
106{
107
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108}
109#endif
110
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111/* Global quiescent period parity */
112extern int urcu_qparity;
113
114extern int __thread urcu_active_readers[2];
115
116static inline int get_urcu_qparity(void)
117{
118 return urcu_qparity;
119}
120
121/*
c265818b 122 * urcu_parity should be declared on the caller's stack.
27b012e2 123 */
c265818b 124static inline void rcu_read_lock(int *urcu_parity)
27b012e2 125{
cf380c2f 126 debug_yield_read();
c265818b 127 *urcu_parity = get_urcu_qparity();
cf380c2f 128 debug_yield_read();
c265818b 129 urcu_active_readers[*urcu_parity]++;
cf380c2f 130 debug_yield_read();
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131 /*
132 * Increment active readers count before accessing the pointer.
133 * See force_mb_all_threads().
134 */
135 barrier();
cf380c2f 136 debug_yield_read();
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137}
138
c265818b 139static inline void rcu_read_unlock(int *urcu_parity)
27b012e2 140{
cf380c2f 141 debug_yield_read();
27b012e2 142 barrier();
cf380c2f 143 debug_yield_read();
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144 /*
145 * Finish using rcu before decrementing the pointer.
146 * See force_mb_all_threads().
147 */
c265818b 148 urcu_active_readers[*urcu_parity]--;
cf380c2f 149 debug_yield_read();
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150}
151
cdcb92bb 152extern void *urcu_publish_content(void **ptr, void *new);
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153
154/*
155 * Reader thread registration.
156 */
157extern void urcu_register_thread(void);
5e7e64b9 158extern void urcu_unregister_thread(void);
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159
160#endif /* _URCU_H */
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