X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=include%2Furcu%2Fstatic%2Fpointer.h;fp=include%2Furcu%2Fstatic%2Fpointer.h;h=732f8c078d7dcf585bde531cdacd51154818a211;hp=0000000000000000000000000000000000000000;hb=6cd23d474d3b7d3d090652d0d0b9508ab7d1f9f8;hpb=89d19b437b1467f98ecee4190d1160e99111671f diff --git a/include/urcu/static/pointer.h b/include/urcu/static/pointer.h new file mode 100644 index 0000000..732f8c0 --- /dev/null +++ b/include/urcu/static/pointer.h @@ -0,0 +1,146 @@ +#ifndef _URCU_POINTER_STATIC_H +#define _URCU_POINTER_STATIC_H + +/* + * urcu/static/pointer.h + * + * Userspace RCU header. Operations on pointers. + * + * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU + * RELEASE. See urcu.h for linking dynamically with the userspace rcu library. + * + * Copyright (c) 2009 Mathieu Desnoyers + * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + * + * IBM's contributions to this file may be relicensed under LGPLv2 or later. + */ + +#include +#include +#include +#include + +#ifdef __cplusplus +extern "C" { +#endif + +/** + * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable + * into a RCU read-side critical section. The pointer can later be safely + * dereferenced within the critical section. + * + * This ensures that the pointer copy is invariant thorough the whole critical + * section. + * + * Inserts memory barriers on architectures that require them (currently only + * Alpha) and documents which pointers are protected by RCU. + * + * The compiler memory barrier in CMM_LOAD_SHARED() ensures that value-speculative + * optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the + * data read before the pointer read by speculating the value of the pointer. + * Correct ordering is ensured because the pointer is read as a volatile access. + * This acts as a global side-effect operation, which forbids reordering of + * dependent memory operations. Note that such concern about dependency-breaking + * optimizations will eventually be taken care of by the "memory_order_consume" + * addition to forthcoming C++ standard. + * + * Should match rcu_assign_pointer() or rcu_xchg_pointer(). + * + * This macro is less than 10 lines long. The intent is that this macro + * meets the 10-line criterion in LGPL, allowing this function to be + * expanded directly in non-LGPL code. + */ +#define _rcu_dereference(p) \ + __extension__ \ + ({ \ + __typeof__(p) _________p1 = CMM_LOAD_SHARED(p); \ + cmm_smp_read_barrier_depends(); \ + (_________p1); \ + }) + +/** + * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer + * is as expected by "old". If succeeds, returns the previous pointer to the + * data structure, which can be safely freed after waiting for a quiescent state + * using synchronize_rcu(). If fails (unexpected value), returns old (which + * should not be freed !). + * + * uatomic_cmpxchg() acts as both release and acquire barriers. + * + * This macro is less than 10 lines long. The intent is that this macro + * meets the 10-line criterion in LGPL, allowing this function to be + * expanded directly in non-LGPL code. + */ +#define _rcu_cmpxchg_pointer(p, old, _new) \ + __extension__ \ + ({ \ + __typeof__(*p) _________pold = (old); \ + __typeof__(*p) _________pnew = (_new); \ + uatomic_cmpxchg(p, _________pold, _________pnew); \ + }) + +/** + * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous + * pointer to the data structure, which can be safely freed after waiting for a + * quiescent state using synchronize_rcu(). + * + * uatomic_xchg() acts as both release and acquire barriers. + * + * This macro is less than 10 lines long. The intent is that this macro + * meets the 10-line criterion in LGPL, allowing this function to be + * expanded directly in non-LGPL code. + */ +#define _rcu_xchg_pointer(p, v) \ + __extension__ \ + ({ \ + __typeof__(*p) _________pv = (v); \ + uatomic_xchg(p, _________pv); \ + }) + + +#define _rcu_set_pointer(p, v) \ + do { \ + __typeof__(*p) _________pv = (v); \ + if (!__builtin_constant_p(v) || \ + ((v) != NULL)) \ + cmm_wmb(); \ + uatomic_set(p, _________pv); \ + } while (0) + +/** + * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure + * meant to be read by RCU read-side critical sections. Returns the assigned + * value. + * + * Documents which pointers will be dereferenced by RCU read-side critical + * sections and adds the required memory barriers on architectures requiring + * them. It also makes sure the compiler does not reorder code initializing the + * data structure before its publication. + * + * Should match rcu_dereference(). + * + * This macro is less than 10 lines long. The intent is that this macro + * meets the 10-line criterion in LGPL, allowing this function to be + * expanded directly in non-LGPL code. + */ +#define _rcu_assign_pointer(p, v) _rcu_set_pointer(&(p), v) + +#ifdef __cplusplus +} +#endif + +#endif /* _URCU_POINTER_STATIC_H */