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7e30abe3 MD |
1 | #ifndef _URCU_POINTER_STATIC_H |
2 | #define _URCU_POINTER_STATIC_H | |
3 | ||
4 | /* | |
6cd23d47 | 5 | * urcu/static/pointer.h |
7e30abe3 MD |
6 | * |
7 | * Userspace RCU header. Operations on pointers. | |
8 | * | |
a5a9f428 PM |
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. | |
7e30abe3 | 11 | * |
6982d6d7 | 12 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
7e30abe3 MD |
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> | |
a2e7bf9c | 35 | #include <urcu/uatomic.h> |
7e30abe3 | 36 | |
36bc70a8 MD |
37 | #ifdef __cplusplus |
38 | extern "C" { | |
67ecffc0 | 39 | #endif |
36bc70a8 | 40 | |
7e30abe3 MD |
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 | * | |
380f4b19 MD |
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 | * | |
3abcdbd1 MD |
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 | * | |
380f4b19 MD |
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. | |
7e30abe3 MD |
79 | * |
80 | * Should match rcu_assign_pointer() or rcu_xchg_pointer(). | |
a5a9f428 PM |
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. | |
7e30abe3 | 85 | */ |
380f4b19 | 86 | |
3abcdbd1 MD |
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 | |
380f4b19 MD |
91 | #endif |
92 | ||
3abcdbd1 MD |
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 | |
7e30abe3 MD |
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 !). | |
a5a9f428 | 113 | * |
2f10494a MD |
114 | * uatomic_cmpxchg() acts as both release and acquire barriers. |
115 | * | |
a5a9f428 PM |
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. | |
7e30abe3 | 119 | */ |
2b5554c9 | 120 | #define _rcu_cmpxchg_pointer(p, old, _new) \ |
1b85da85 | 121 | __extension__ \ |
2b5554c9 | 122 | ({ \ |
bdffa73a MD |
123 | __typeof__(*p) _________pold = (old); \ |
124 | __typeof__(*p) _________pnew = (_new); \ | |
bf9de1b7 | 125 | uatomic_cmpxchg(p, _________pold, _________pnew); \ |
7e30abe3 MD |
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(). | |
a5a9f428 | 132 | * |
2f10494a MD |
133 | * uatomic_xchg() acts as both release and acquire barriers. |
134 | * | |
a5a9f428 PM |
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. | |
7e30abe3 | 138 | */ |
7e30abe3 | 139 | #define _rcu_xchg_pointer(p, v) \ |
1b85da85 | 140 | __extension__ \ |
7e30abe3 | 141 | ({ \ |
bdffa73a | 142 | __typeof__(*p) _________pv = (v); \ |
2b5554c9 | 143 | uatomic_xchg(p, _________pv); \ |
7e30abe3 MD |
144 | }) |
145 | ||
146 | ||
147 | #define _rcu_set_pointer(p, v) \ | |
3daae22a | 148 | do { \ |
bdffa73a | 149 | __typeof__(*p) _________pv = (v); \ |
7e30abe3 MD |
150 | if (!__builtin_constant_p(v) || \ |
151 | ((v) != NULL)) \ | |
5481ddb3 | 152 | cmm_wmb(); \ |
bf9de1b7 | 153 | uatomic_set(p, _________pv); \ |
3daae22a | 154 | } while (0) |
7e30abe3 | 155 | |
7e30abe3 MD |
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 | * | |
edf8de69 | 166 | * Should match rcu_dereference(). |
a5a9f428 PM |
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. | |
7e30abe3 | 171 | */ |
7e30abe3 MD |
172 | #define _rcu_assign_pointer(p, v) _rcu_set_pointer(&(p), v) |
173 | ||
67ecffc0 | 174 | #ifdef __cplusplus |
36bc70a8 MD |
175 | } |
176 | #endif | |
177 | ||
7e30abe3 | 178 | #endif /* _URCU_POINTER_STATIC_H */ |