Add DEBUG_YIELD, add test duration
[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
75extern int yield_active;
76
77static inline void debug_yield_read(void)
78{
79 if (yield_active & YIELD_READ)
80 sched_yield();
81}
82
83static inline void debug_yield_write(void)
84{
85 if (yield_active & YIELD_WRITE)
86 sched_yield();
87}
88#else
89static inline void debug_yield_read(void)
90{
91}
92
93static inline void debug_yield_write(void)
94{
95}
96#endif
97
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98/* Global quiescent period parity */
99extern int urcu_qparity;
100
101extern int __thread urcu_active_readers[2];
102
103static inline int get_urcu_qparity(void)
104{
105 return urcu_qparity;
106}
107
108/*
c265818b 109 * urcu_parity should be declared on the caller's stack.
27b012e2 110 */
c265818b 111static inline void rcu_read_lock(int *urcu_parity)
27b012e2 112{
cf380c2f 113 debug_yield_read();
c265818b 114 *urcu_parity = get_urcu_qparity();
cf380c2f 115 debug_yield_read();
c265818b 116 urcu_active_readers[*urcu_parity]++;
cf380c2f 117 debug_yield_read();
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118 /*
119 * Increment active readers count before accessing the pointer.
120 * See force_mb_all_threads().
121 */
122 barrier();
cf380c2f 123 debug_yield_read();
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124}
125
c265818b 126static inline void rcu_read_unlock(int *urcu_parity)
27b012e2 127{
cf380c2f 128 debug_yield_read();
27b012e2 129 barrier();
cf380c2f 130 debug_yield_read();
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131 /*
132 * Finish using rcu before decrementing the pointer.
133 * See force_mb_all_threads().
134 */
c265818b 135 urcu_active_readers[*urcu_parity]--;
cf380c2f 136 debug_yield_read();
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137}
138
cdcb92bb 139extern void *urcu_publish_content(void **ptr, void *new);
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140
141/*
142 * Reader thread registration.
143 */
144extern void urcu_register_thread(void);
5e7e64b9 145extern void urcu_unregister_thread(void);
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146
147#endif /* _URCU_H */
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