ca9a2f9836760dd01207508d2615ee9f43d4e555
[urcu.git] / include / urcu / static / pointer.h
1 #ifndef _URCU_POINTER_STATIC_H
2 #define _URCU_POINTER_STATIC_H
3
4 /*
5 * urcu/static/pointer.h
6 *
7 * Userspace RCU header. Operations on pointers.
8 *
9 * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
10 * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
11 *
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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.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 * With C standards prior to C11/C++11, the compiler memory barrier in
53 * CMM_LOAD_SHARED() ensures that value-speculative optimizations (e.g.
54 * VSS: Value Speculation Scheduling) does not perform the data read
55 * before the pointer read by speculating the value of the pointer.
56 * Correct ordering is ensured because the pointer is read as a volatile
57 * access. This acts as a global side-effect operation, which forbids
58 * reordering of dependent memory operations.
59 *
60 * With C standards C11/C++11, concerns about dependency-breaking
61 * optimizations are taken care of by the "memory_order_consume" atomic
62 * load.
63 *
64 * Use the gcc __atomic_load() rather than C11/C++11 atomic load
65 * explicit because the pointer used as input argument is a pointer,
66 * not an _Atomic type as required by C11/C++11.
67 *
68 * By defining URCU_DEREFERENCE_USE_VOLATILE, the user requires use of
69 * volatile access to implement rcu_dereference rather than
70 * memory_order_consume load from the C11/C++11 standards.
71 *
72 * This may improve performance on weakly-ordered architectures where
73 * the compiler implements memory_order_consume as a
74 * memory_order_acquire, which is stricter than required by the
75 * standard.
76 *
77 * Note that using volatile accesses for rcu_dereference may cause
78 * LTO to generate incorrectly ordered code starting from C11/C++11.
79 *
80 * Should match rcu_assign_pointer() or rcu_xchg_pointer().
81 *
82 * This macro is less than 10 lines long. The intent is that this macro
83 * meets the 10-line criterion in LGPL, allowing this function to be
84 * expanded directly in non-LGPL code.
85 */
86
87 #if !defined (URCU_DEREFERENCE_USE_VOLATILE) && \
88 ((defined (__cplusplus) && __cplusplus >= 201103L) || \
89 (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L))
90 # define __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
91 #endif
92
93 #ifdef __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
94 # define _rcu_dereference(p) __extension__ ({ \
95 __typeof__(p) _________p1; \
96 __atomic_load(&(p), &_________p1, __ATOMIC_CONSUME); \
97 (_________p1); \
98 })
99 #else
100 # define _rcu_dereference(p) __extension__ ({ \
101 __typeof__(p) _________p1 = CMM_LOAD_SHARED(p); \
102 cmm_smp_read_barrier_depends(); \
103 (_________p1); \
104 })
105 #endif
106
107 /**
108 * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
109 * is as expected by "old". If succeeds, returns the previous pointer to the
110 * data structure, which can be safely freed after waiting for a quiescent state
111 * using synchronize_rcu(). If fails (unexpected value), returns old (which
112 * should not be freed !).
113 *
114 * uatomic_cmpxchg() acts as both release and acquire barriers.
115 *
116 * This macro is less than 10 lines long. The intent is that this macro
117 * meets the 10-line criterion in LGPL, allowing this function to be
118 * expanded directly in non-LGPL code.
119 */
120 #define _rcu_cmpxchg_pointer(p, old, _new) \
121 __extension__ \
122 ({ \
123 __typeof__(*p) _________pold = (old); \
124 __typeof__(*p) _________pnew = (_new); \
125 uatomic_cmpxchg(p, _________pold, _________pnew); \
126 })
127
128 /**
129 * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
130 * pointer to the data structure, which can be safely freed after waiting for a
131 * quiescent state using synchronize_rcu().
132 *
133 * uatomic_xchg() acts as both release and acquire barriers.
134 *
135 * This macro is less than 10 lines long. The intent is that this macro
136 * meets the 10-line criterion in LGPL, allowing this function to be
137 * expanded directly in non-LGPL code.
138 */
139 #define _rcu_xchg_pointer(p, v) \
140 __extension__ \
141 ({ \
142 __typeof__(*p) _________pv = (v); \
143 uatomic_xchg(p, _________pv); \
144 })
145
146
147 #define _rcu_set_pointer(p, v) \
148 do { \
149 __typeof__(*p) _________pv = (v); \
150 if (!__builtin_constant_p(v) || \
151 ((v) != NULL)) \
152 cmm_wmb(); \
153 uatomic_set(p, _________pv); \
154 } while (0)
155
156 /**
157 * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
158 * meant to be read by RCU read-side critical sections. Returns the assigned
159 * value.
160 *
161 * Documents which pointers will be dereferenced by RCU read-side critical
162 * sections and adds the required memory barriers on architectures requiring
163 * them. It also makes sure the compiler does not reorder code initializing the
164 * data structure before its publication.
165 *
166 * Should match rcu_dereference().
167 *
168 * This macro is less than 10 lines long. The intent is that this macro
169 * meets the 10-line criterion in LGPL, allowing this function to be
170 * expanded directly in non-LGPL code.
171 */
172 #define _rcu_assign_pointer(p, v) _rcu_set_pointer(&(p), v)
173
174 #ifdef __cplusplus
175 }
176 #endif
177
178 #endif /* _URCU_POINTER_STATIC_H */
This page took 0.047821 seconds and 4 git commands to generate.