URCU : use pthread_equal()
[urcu.git] / urcu.h
1 #ifndef _URCU_H
2 #define _URCU_H
3
4 /*
5 * urcu.h
6 *
7 * Userspace RCU header
8 *
9 * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
10 *
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 *
17 * Distributed under GPLv2
18 */
19
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
28 static inline void atomic_inc(int *v)
29 {
30 asm volatile("lock; incl %0"
31 : "+m" (*v));
32 }
33
34 /* Nop everywhere except on alpha. */
35 #define smp_read_barrier_depends()
36
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
67 #define SIGURCU SIGUSR1
68
69 /* Global quiescent period parity */
70 extern int urcu_qparity;
71
72 extern int __thread urcu_active_readers[2];
73
74 static inline int get_urcu_qparity(void)
75 {
76 return urcu_qparity;
77 }
78
79 /*
80 * returns urcu_parity.
81 */
82 static inline int rcu_read_lock(void)
83 {
84 int urcu_parity = get_urcu_qparity();
85 urcu_active_readers[urcu_parity]++;
86 /*
87 * Increment active readers count before accessing the pointer.
88 * See force_mb_all_threads().
89 */
90 barrier();
91 return urcu_parity;
92 }
93
94 static inline void rcu_read_unlock(int urcu_parity)
95 {
96 barrier();
97 /*
98 * Finish using rcu before decrementing the pointer.
99 * See force_mb_all_threads().
100 */
101 urcu_active_readers[urcu_parity]--;
102 }
103
104 extern void rcu_write_lock(void);
105 extern void rcu_write_unlock(void);
106
107 extern void *urcu_publish_content(void **ptr, void *new);
108
109 /*
110 * Reader thread registration.
111 */
112 extern void urcu_register_thread(void);
113 extern void urcu_unregister_thread(void);
114
115 #endif /* _URCU_H */
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