include/urcu/static/urcu-pointer.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 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 _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 _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 _rcu_xchg_pointer(p, v)                         \
 108         __extension__                                   \
 109         ({                                              \
 110                 __typeof__(*p) _________pv = (v);       \
 111                 uatomic_xchg(p, _________pv);           \
 112         })
 113
 114
 115 #define _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 _rcu_assign_pointer(p, v)       _rcu_set_pointer(&(p), v)
 141
 142 #ifdef __cplusplus
 143 }
 144 #endif
 145
 146 #endif /* _URCU_POINTER_STATIC_H */