Add extern "C" to support linking userspace RCU library with C++ applications
[urcu.git] / urcu-pointer-static.h
1 #ifndef _URCU_POINTER_STATIC_H
2 #define _URCU_POINTER_STATIC_H
3
4 /*
5 * urcu-pointer-static.h
6 *
7 * Userspace RCU header. Operations on pointers.
8 *
9 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-pointer.h for
10 * linking dynamically with the userspace rcu library.
11 *
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
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 <urcu/compiler.h>
33 #include <urcu/arch.h>
34 #include <urcu/system.h>
35 #include <urcu/uatomic_arch.h>
36
37 #ifdef __cplusplus
38 extern "C" {
39 #endif
40
41 /**
42 * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
43 * into a RCU read-side critical section. The pointer can later be safely
44 * dereferenced within the critical section.
45 *
46 * This ensures that the pointer copy is invariant thorough the whole critical
47 * section.
48 *
49 * Inserts memory barriers on architectures that require them (currently only
50 * Alpha) and documents which pointers are protected by RCU.
51 *
52 * The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
53 * optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
54 * data read before the pointer read by speculating the value of the pointer.
55 * Correct ordering is ensured because the pointer is read as a volatile access.
56 * This acts as a global side-effect operation, which forbids reordering of
57 * dependent memory operations. Note that such concern about dependency-breaking
58 * optimizations will eventually be taken care of by the "memory_order_consume"
59 * addition to forthcoming C++ standard.
60 *
61 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
62 */
63
64 #define _rcu_dereference(p) ({ \
65 typeof(p) _________p1 = LOAD_SHARED(p); \
66 smp_read_barrier_depends(); \
67 (_________p1); \
68 })
69
70 /**
71 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
72 * is as expected by "old". If succeeds, returns the previous pointer to the
73 * data structure, which can be safely freed after waiting for a quiescent state
74 * using synchronize_rcu(). If fails (unexpected value), returns old (which
75 * should not be freed !).
76 */
77
78 #define _rcu_cmpxchg_pointer(p, old, _new) \
79 ({ \
80 typeof(*p) _________pold = (old); \
81 typeof(*p) _________pnew = (_new); \
82 if (!__builtin_constant_p(_new) || \
83 ((_new) != NULL)) \
84 wmb(); \
85 uatomic_cmpxchg(p, _________pold, _________pnew); \
86 })
87
88 /**
89 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
90 * pointer to the data structure, which can be safely freed after waiting for a
91 * quiescent state using synchronize_rcu().
92 */
93
94 #define _rcu_xchg_pointer(p, v) \
95 ({ \
96 typeof(*p) _________pv = (v); \
97 if (!__builtin_constant_p(v) || \
98 ((v) != NULL)) \
99 wmb(); \
100 uatomic_xchg(p, _________pv); \
101 })
102
103
104 #define _rcu_set_pointer(p, v) \
105 ({ \
106 typeof(*p) _________pv = (v); \
107 if (!__builtin_constant_p(v) || \
108 ((v) != NULL)) \
109 wmb(); \
110 uatomic_set(p, _________pv); \
111 })
112
113 /**
114 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
115 * meant to be read by RCU read-side critical sections. Returns the assigned
116 * value.
117 *
118 * Documents which pointers will be dereferenced by RCU read-side critical
119 * sections and adds the required memory barriers on architectures requiring
120 * them. It also makes sure the compiler does not reorder code initializing the
121 * data structure before its publication.
122 *
123 * Should match rcu_dereference_pointer().
124 */
125
126 #define _rcu_assign_pointer(p, v) _rcu_set_pointer(&(p), v)
127
128 #ifdef __cplusplus
129 }
130 #endif
131
132 #endif /* _URCU_POINTER_STATIC_H */
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