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[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
69/* Global quiescent period parity */
70extern int urcu_qparity;
71
72extern int __thread urcu_active_readers[2];
73
74static inline int get_urcu_qparity(void)
75{
76 return urcu_qparity;
77}
78
79/*
c265818b 80 * urcu_parity should be declared on the caller's stack.
27b012e2 81 */
c265818b 82static inline void rcu_read_lock(int *urcu_parity)
27b012e2 83{
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84 *urcu_parity = get_urcu_qparity();
85 urcu_active_readers[*urcu_parity]++;
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86 /*
87 * Increment active readers count before accessing the pointer.
88 * See force_mb_all_threads().
89 */
90 barrier();
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91}
92
c265818b 93static inline void rcu_read_unlock(int *urcu_parity)
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94{
95 barrier();
96 /*
97 * Finish using rcu before decrementing the pointer.
98 * See force_mb_all_threads().
99 */
c265818b 100 urcu_active_readers[*urcu_parity]--;
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101}
102
cdcb92bb 103extern void *urcu_publish_content(void **ptr, void *new);
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104
105/*
106 * Reader thread registration.
107 */
108extern void urcu_register_thread(void);
5e7e64b9 109extern void urcu_unregister_thread(void);
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110
111#endif /* _URCU_H */
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