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1 | // SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
2 | // SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation. | |
3 | // | |
4 | // SPDX-License-Identifier: LGPL-2.1-or-later | |
5 | ||
7e30abe3 MD |
6 | #ifndef _URCU_POINTER_STATIC_H |
7 | #define _URCU_POINTER_STATIC_H | |
8 | ||
9 | /* | |
7e30abe3 MD |
10 | * Userspace RCU header. Operations on pointers. |
11 | * | |
a5a9f428 PM |
12 | * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU |
13 | * RELEASE. See urcu.h for linking dynamically with the userspace rcu library. | |
7e30abe3 | 14 | * |
7e30abe3 MD |
15 | * IBM's contributions to this file may be relicensed under LGPLv2 or later. |
16 | */ | |
17 | ||
18 | #include <urcu/compiler.h> | |
19 | #include <urcu/arch.h> | |
20 | #include <urcu/system.h> | |
a2e7bf9c | 21 | #include <urcu/uatomic.h> |
7e30abe3 | 22 | |
36bc70a8 MD |
23 | #ifdef __cplusplus |
24 | extern "C" { | |
67ecffc0 | 25 | #endif |
36bc70a8 | 26 | |
7e30abe3 MD |
27 | /** |
28 | * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable | |
29 | * into a RCU read-side critical section. The pointer can later be safely | |
30 | * dereferenced within the critical section. | |
31 | * | |
32 | * This ensures that the pointer copy is invariant thorough the whole critical | |
33 | * section. | |
34 | * | |
35 | * Inserts memory barriers on architectures that require them (currently only | |
36 | * Alpha) and documents which pointers are protected by RCU. | |
37 | * | |
380f4b19 MD |
38 | * With C standards prior to C11/C++11, the compiler memory barrier in |
39 | * CMM_LOAD_SHARED() ensures that value-speculative optimizations (e.g. | |
40 | * VSS: Value Speculation Scheduling) does not perform the data read | |
41 | * before the pointer read by speculating the value of the pointer. | |
42 | * Correct ordering is ensured because the pointer is read as a volatile | |
43 | * access. This acts as a global side-effect operation, which forbids | |
44 | * reordering of dependent memory operations. | |
45 | * | |
46 | * With C standards C11/C++11, concerns about dependency-breaking | |
47 | * optimizations are taken care of by the "memory_order_consume" atomic | |
48 | * load. | |
49 | * | |
3abcdbd1 MD |
50 | * Use the gcc __atomic_load() rather than C11/C++11 atomic load |
51 | * explicit because the pointer used as input argument is a pointer, | |
52 | * not an _Atomic type as required by C11/C++11. | |
53 | * | |
380f4b19 MD |
54 | * By defining URCU_DEREFERENCE_USE_VOLATILE, the user requires use of |
55 | * volatile access to implement rcu_dereference rather than | |
56 | * memory_order_consume load from the C11/C++11 standards. | |
57 | * | |
58 | * This may improve performance on weakly-ordered architectures where | |
59 | * the compiler implements memory_order_consume as a | |
60 | * memory_order_acquire, which is stricter than required by the | |
61 | * standard. | |
62 | * | |
63 | * Note that using volatile accesses for rcu_dereference may cause | |
64 | * LTO to generate incorrectly ordered code starting from C11/C++11. | |
7e30abe3 MD |
65 | * |
66 | * Should match rcu_assign_pointer() or rcu_xchg_pointer(). | |
a5a9f428 PM |
67 | * |
68 | * This macro is less than 10 lines long. The intent is that this macro | |
69 | * meets the 10-line criterion in LGPL, allowing this function to be | |
70 | * expanded directly in non-LGPL code. | |
7e30abe3 | 71 | */ |
380f4b19 | 72 | |
3abcdbd1 MD |
73 | #if !defined (URCU_DEREFERENCE_USE_VOLATILE) && \ |
74 | ((defined (__cplusplus) && __cplusplus >= 201103L) || \ | |
75 | (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L)) | |
76 | # define __URCU_DEREFERENCE_USE_ATOMIC_CONSUME | |
380f4b19 MD |
77 | #endif |
78 | ||
1e41ec3b SM |
79 | /* |
80 | * If p is const (the pointer itself, not what it points to), using | |
81 | * __typeof__(p) would declare a const variable, leading to | |
2d466a63 SM |
82 | * -Wincompatible-pointer-types errors. Using the statement expression |
83 | * makes it an rvalue and gets rid of the const-ness. | |
1e41ec3b | 84 | */ |
d1854484 OD |
85 | # define _rcu_dereference(p) \ |
86 | uatomic_load(&(p), CMM_CONSUME) | |
7e30abe3 MD |
87 | /** |
88 | * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer | |
89 | * is as expected by "old". If succeeds, returns the previous pointer to the | |
90 | * data structure, which can be safely freed after waiting for a quiescent state | |
91 | * using synchronize_rcu(). If fails (unexpected value), returns old (which | |
92 | * should not be freed !). | |
a5a9f428 | 93 | * |
d1854484 | 94 | * uatomic_cmpxchg() acts as both release and acquire barriers on success. |
2f10494a | 95 | * |
a5a9f428 PM |
96 | * This macro is less than 10 lines long. The intent is that this macro |
97 | * meets the 10-line criterion in LGPL, allowing this function to be | |
98 | * expanded directly in non-LGPL code. | |
7e30abe3 | 99 | */ |
2b5554c9 | 100 | #define _rcu_cmpxchg_pointer(p, old, _new) \ |
1b85da85 | 101 | __extension__ \ |
2b5554c9 | 102 | ({ \ |
bdffa73a MD |
103 | __typeof__(*p) _________pold = (old); \ |
104 | __typeof__(*p) _________pnew = (_new); \ | |
d1854484 OD |
105 | uatomic_cmpxchg_mo(p, _________pold, _________pnew, \ |
106 | CMM_SEQ_CST, CMM_RELAXED); \ | |
107 | }); | |
7e30abe3 MD |
108 | |
109 | /** | |
110 | * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous | |
111 | * pointer to the data structure, which can be safely freed after waiting for a | |
112 | * quiescent state using synchronize_rcu(). | |
a5a9f428 | 113 | * |
2f10494a MD |
114 | * uatomic_xchg() 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 | */ |
7e30abe3 | 120 | #define _rcu_xchg_pointer(p, v) \ |
1b85da85 | 121 | __extension__ \ |
7e30abe3 | 122 | ({ \ |
bdffa73a | 123 | __typeof__(*p) _________pv = (v); \ |
d1854484 OD |
124 | uatomic_xchg_mo(p, _________pv, \ |
125 | CMM_SEQ_CST); \ | |
7e30abe3 MD |
126 | }) |
127 | ||
128 | ||
d1854484 OD |
129 | #define _rcu_set_pointer(p, v) \ |
130 | do { \ | |
131 | __typeof__(*p) _________pv = (v); \ | |
132 | uatomic_store(p, _________pv, \ | |
133 | __builtin_constant_p(v) && (v) == NULL ? \ | |
134 | CMM_RELAXED : CMM_RELEASE); \ | |
3daae22a | 135 | } while (0) |
7e30abe3 | 136 | |
7e30abe3 MD |
137 | /** |
138 | * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure | |
139 | * meant to be read by RCU read-side critical sections. Returns the assigned | |
140 | * value. | |
141 | * | |
142 | * Documents which pointers will be dereferenced by RCU read-side critical | |
143 | * sections and adds the required memory barriers on architectures requiring | |
144 | * them. It also makes sure the compiler does not reorder code initializing the | |
145 | * data structure before its publication. | |
146 | * | |
edf8de69 | 147 | * Should match rcu_dereference(). |
a5a9f428 PM |
148 | * |
149 | * This macro is less than 10 lines long. The intent is that this macro | |
150 | * meets the 10-line criterion in LGPL, allowing this function to be | |
151 | * expanded directly in non-LGPL code. | |
7e30abe3 | 152 | */ |
7e30abe3 MD |
153 | #define _rcu_assign_pointer(p, v) _rcu_set_pointer(&(p), v) |
154 | ||
67ecffc0 | 155 | #ifdef __cplusplus |
36bc70a8 MD |
156 | } |
157 | #endif | |
158 | ||
7e30abe3 | 159 | #endif /* _URCU_POINTER_STATIC_H */ |