urcu-pointer-static.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 LGPL-COMPATIBLE CODE. See urcu-pointer.h for
  10  * linking dynamically with the userspace rcu library.
  11  *
  12  * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
  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_arch.h>
  36
  37 /**
  38  * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
  39  * into a RCU read-side critical section. The pointer can later be safely
  40  * dereferenced within the critical section.
  41  *
  42  * This ensures that the pointer copy is invariant thorough the whole critical
  43  * section.
  44  *
  45  * Inserts memory barriers on architectures that require them (currently only
  46  * Alpha) and documents which pointers are protected by RCU.
  47  *
  48  * The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
  49  * optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
  50  * data read before the pointer read by speculating the value of the pointer.
  51  * Correct ordering is ensured because the pointer is read as a volatile access.
  52  * This acts as a global side-effect operation, which forbids reordering of
  53  * dependent memory operations. Note that such concern about dependency-breaking
  54  * optimizations will eventually be taken care of by the "memory_order_consume"
  55  * addition to forthcoming C++ standard.
  56  *
  57  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  58  */
  59
  60 #define _rcu_dereference(p)     ({                                      \
  61                                 typeof(p) _________p1 = LOAD_SHARED(p); \
  62                                 smp_read_barrier_depends();             \
  63                                 (_________p1);                          \
  64                                 })
  65
  66 /**
  67  * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
  68  * is as expected by "old". If succeeds, returns the previous pointer to the
  69  * data structure, which can be safely freed after waiting for a quiescent state
  70  * using synchronize_rcu(). If fails (unexpected value), returns old (which
  71  * should not be freed !).
  72  */
  73
  74 #define _rcu_cmpxchg_pointer(p, old, _new)                              \
  75         ({                                                              \
  76                 typeof(*p) _________pold = (old);                       \
  77                 typeof(*p) _________pnew = (_new);                      \
  78                 if (!__builtin_constant_p(_new) ||                      \
  79                     ((_new) != NULL))                                   \
  80                         wmb();                                          \
  81                 uatomic_cmpxchg(p, _________pold, _________pnew);       \
  82         })
  83
  84 /**
  85  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
  86  * pointer to the data structure, which can be safely freed after waiting for a
  87  * quiescent state using synchronize_rcu().
  88  */
  89
  90 #define _rcu_xchg_pointer(p, v)                         \
  91         ({                                              \
  92                 typeof(*p) _________pv = (v);           \
  93                 if (!__builtin_constant_p(v) ||         \
  94                     ((v) != NULL))                      \
  95                         wmb();                          \
  96                 uatomic_xchg(p, _________pv);           \
  97         })
  98
  99
 100 #define _rcu_set_pointer(p, v)                          \
 101         ({                                              \
 102                 typeof(*p) _________pv = (v);           \
 103                 if (!__builtin_constant_p(v) ||         \
 104                     ((v) != NULL))                      \
 105                         wmb();                          \
 106                 uatomic_set(p, _________pv);            \
 107         })
 108
 109 /**
 110  * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
 111  * meant to be read by RCU read-side critical sections. Returns the assigned
 112  * value.
 113  *
 114  * Documents which pointers will be dereferenced by RCU read-side critical
 115  * sections and adds the required memory barriers on architectures requiring
 116  * them. It also makes sure the compiler does not reorder code initializing the
 117  * data structure before its publication.
 118  *
 119  * Should match rcu_dereference_pointer().
 120  */
 121
 122 #define _rcu_assign_pointer(p, v)       _rcu_set_pointer(&(p), v)
 123
 124 #endif /* _URCU_POINTER_STATIC_H */