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1 | #ifndef _LTTNG_URCU_POINTER_STATIC_H |
2 | #define _LTTNG_URCU_POINTER_STATIC_H | |
3 | ||
4 | /* | |
5 | * lttng/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 | * The compiler memory barrier in CMM_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 | * This macro is less than 10 lines long. The intent is that this macro | |
64 | * meets the 10-line criterion in LGPL, allowing this function to be | |
65 | * expanded directly in non-LGPL code. | |
66 | */ | |
67 | #define _lttng_ust_rcu_dereference(p) \ | |
68 | __extension__ \ | |
69 | ({ \ | |
70 | __typeof__(p) _________p1 = CMM_LOAD_SHARED(p); \ | |
71 | cmm_smp_read_barrier_depends(); \ | |
72 | (_________p1); \ | |
73 | }) | |
74 | ||
75 | /** | |
76 | * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer | |
77 | * is as expected by "old". If succeeds, returns the previous pointer to the | |
78 | * data structure, which can be safely freed after waiting for a quiescent state | |
79 | * using synchronize_rcu(). If fails (unexpected value), returns old (which | |
80 | * should not be freed !). | |
81 | * | |
82 | * uatomic_cmpxchg() acts as both release and acquire barriers. | |
83 | * | |
84 | * This macro is less than 10 lines long. The intent is that this macro | |
85 | * meets the 10-line criterion in LGPL, allowing this function to be | |
86 | * expanded directly in non-LGPL code. | |
87 | */ | |
88 | #define _lttng_ust_rcu_cmpxchg_pointer(p, old, _new) \ | |
89 | __extension__ \ | |
90 | ({ \ | |
91 | __typeof__(*p) _________pold = (old); \ | |
92 | __typeof__(*p) _________pnew = (_new); \ | |
93 | uatomic_cmpxchg(p, _________pold, _________pnew); \ | |
94 | }) | |
95 | ||
96 | /** | |
97 | * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous | |
98 | * pointer to the data structure, which can be safely freed after waiting for a | |
99 | * quiescent state using synchronize_rcu(). | |
100 | * | |
101 | * uatomic_xchg() acts as both release and acquire barriers. | |
102 | * | |
103 | * This macro is less than 10 lines long. The intent is that this macro | |
104 | * meets the 10-line criterion in LGPL, allowing this function to be | |
105 | * expanded directly in non-LGPL code. | |
106 | */ | |
107 | #define _lttng_ust_rcu_xchg_pointer(p, v) \ | |
108 | __extension__ \ | |
109 | ({ \ | |
110 | __typeof__(*p) _________pv = (v); \ | |
111 | uatomic_xchg(p, _________pv); \ | |
112 | }) | |
113 | ||
114 | ||
115 | #define _lttng_ust_rcu_set_pointer(p, v) \ | |
116 | do { \ | |
117 | __typeof__(*p) _________pv = (v); \ | |
118 | if (!__builtin_constant_p(v) || \ | |
119 | ((v) != NULL)) \ | |
120 | cmm_wmb(); \ | |
121 | uatomic_set(p, _________pv); \ | |
122 | } while (0) | |
123 | ||
124 | /** | |
125 | * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure | |
126 | * meant to be read by RCU read-side critical sections. Returns the assigned | |
127 | * value. | |
128 | * | |
129 | * Documents which pointers will be dereferenced by RCU read-side critical | |
130 | * sections and adds the required memory barriers on architectures requiring | |
131 | * them. It also makes sure the compiler does not reorder code initializing the | |
132 | * data structure before its publication. | |
133 | * | |
134 | * Should match rcu_dereference(). | |
135 | * | |
136 | * This macro is less than 10 lines long. The intent is that this macro | |
137 | * meets the 10-line criterion in LGPL, allowing this function to be | |
138 | * expanded directly in non-LGPL code. | |
139 | */ | |
140 | #define _lttng_ust_rcu_assign_pointer(p, v) _lttng_ust_rcu_set_pointer(&(p), v) | |
141 | ||
142 | #ifdef __cplusplus | |
143 | } | |
144 | #endif | |
145 | ||
146 | #endif /* _LTTNG_URCU_POINTER_STATIC_H */ |