[urcu.git] / include / urcu / static / pointer.h

#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 <mathieu.desnoyers@efficios.com>
 * 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 <urcu/compiler.h>
#include <urcu/arch.h>
#include <urcu/system.h>
#include <urcu/uatomic.h>

#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.
 *
 * With C standards prior to C11/C++11, 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.
 *
 * With C standards C11/C++11, concerns about dependency-breaking
 * optimizations are taken care of by the "memory_order_consume" atomic
 * load.
 *
 * Use the gcc __atomic_load() rather than C11/C++11 atomic load
 * explicit because the pointer used as input argument is a pointer,
 * not an _Atomic type as required by C11/C++11.
 *
 * By defining URCU_DEREFERENCE_USE_VOLATILE, the user requires use of
 * volatile access to implement rcu_dereference rather than
 * memory_order_consume load from the C11/C++11 standards.
 *
 * This may improve performance on weakly-ordered architectures where
 * the compiler implements memory_order_consume as a
 * memory_order_acquire, which is stricter than required by the
 * standard.
 *
 * Note that using volatile accesses for rcu_dereference may cause
 * LTO to generate incorrectly ordered code starting from C11/C++11.
 *
 * 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.
 */

#if !defined (URCU_DEREFERENCE_USE_VOLATILE) &&		\
	((defined (__cplusplus) && __cplusplus >= 201103L) ||	\
	(defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L))
# define __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
#endif

/*
 * If p is const (the pointer itself, not what it points to), using
 * __typeof__(p) would declare a const variable, leading to
 * -Wincompatible-pointer-types errors.  Using `+ 0` makes it an rvalue and
 * gets rid of the const-ness.
 */
#ifdef __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
# define _rcu_dereference(p) __extension__ ({						\
				__typeof__(p + 0) _________p1;				\
				__atomic_load(&(p), &_________p1, __ATOMIC_CONSUME);	\
				(_________p1);						\
			})
#else
# define _rcu_dereference(p) __extension__ ({						\
				__typeof__(p) _________p1 = CMM_LOAD_SHARED(p);		\
				cmm_smp_read_barrier_depends();				\
				(_________p1);						\
			})
#endif

/**
 * _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 */
Commit	Line	Data
7e30abe3 MD	1	#ifndef _URCU_POINTER_STATIC_H
	2	#define _URCU_POINTER_STATIC_H
	3
	4	/*
6cd23d47	5	* urcu/static/pointer.h
7e30abe3 MD	6	*
	7	* Userspace RCU header. Operations on pointers.
	8	*
a5a9f428 PM	9	* TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
a5a9f428 PM	10	* RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
7e30abe3	11	*
6982d6d7	12	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
7e30abe3 MD	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>
a2e7bf9c	35	#include <urcu/uatomic.h>
7e30abe3	36
36bc70a8 MD	37	#ifdef __cplusplus
36bc70a8 MD	38	extern "C" {
67ecffc0	39	#endif
36bc70a8	40
7e30abe3 MD	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	*
380f4b19 MD	52	* With C standards prior to C11/C++11, the compiler memory barrier in
	53	* CMM_LOAD_SHARED() ensures that value-speculative optimizations (e.g.
	54	* VSS: Value Speculation Scheduling) does not perform the data read
	55	* before the pointer read by speculating the value of the pointer.
	56	* Correct ordering is ensured because the pointer is read as a volatile
	57	* access. This acts as a global side-effect operation, which forbids
	58	* reordering of dependent memory operations.
	59	*
	60	* With C standards C11/C++11, concerns about dependency-breaking
	61	* optimizations are taken care of by the "memory_order_consume" atomic
	62	* load.
	63	*
3abcdbd1 MD	64	* Use the gcc __atomic_load() rather than C11/C++11 atomic load
	65	* explicit because the pointer used as input argument is a pointer,
	66	* not an _Atomic type as required by C11/C++11.
	67	*
380f4b19 MD	68	* By defining URCU_DEREFERENCE_USE_VOLATILE, the user requires use of
	69	* volatile access to implement rcu_dereference rather than
	70	* memory_order_consume load from the C11/C++11 standards.
	71	*
	72	* This may improve performance on weakly-ordered architectures where
	73	* the compiler implements memory_order_consume as a
	74	* memory_order_acquire, which is stricter than required by the
	75	* standard.
	76	*
	77	* Note that using volatile accesses for rcu_dereference may cause
	78	* LTO to generate incorrectly ordered code starting from C11/C++11.
7e30abe3 MD	79	*
7e30abe3 MD	80	* Should match rcu_assign_pointer() or rcu_xchg_pointer().
a5a9f428 PM	81	*
	82	* This macro is less than 10 lines long. The intent is that this macro
	83	* meets the 10-line criterion in LGPL, allowing this function to be
	84	* expanded directly in non-LGPL code.
7e30abe3	85	*/
380f4b19	86
3abcdbd1 MD	87	#if !defined (URCU_DEREFERENCE_USE_VOLATILE) && \
	88	((defined (__cplusplus) && __cplusplus >= 201103L) \|\| \
	89	(defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L))
	90	# define __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
380f4b19 MD	91	#endif
380f4b19 MD	92
1e41ec3b SM	93	/*
	94	* If p is const (the pointer itself, not what it points to), using
	95	* __typeof__(p) would declare a const variable, leading to
	96	* -Wincompatible-pointer-types errors. Using `+ 0` makes it an rvalue and
	97	* gets rid of the const-ness.
	98	*/
3abcdbd1 MD	99	#ifdef __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
3abcdbd1 MD	100	# define _rcu_dereference(p) __extension__ ({ \
1e41ec3b	101	__typeof__(p + 0) _________p1; \
3abcdbd1 MD	102	__atomic_load(&(p), &_________p1, __ATOMIC_CONSUME); \
	103	(_________p1); \
	104	})
	105	#else
	106	# define _rcu_dereference(p) __extension__ ({ \
	107	__typeof__(p) _________p1 = CMM_LOAD_SHARED(p); \
	108	cmm_smp_read_barrier_depends(); \
	109	(_________p1); \
	110	})
	111	#endif
7e30abe3 MD	112
	113	/**
	114	* _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
	115	* is as expected by "old". If succeeds, returns the previous pointer to the
	116	* data structure, which can be safely freed after waiting for a quiescent state
	117	* using synchronize_rcu(). If fails (unexpected value), returns old (which
	118	* should not be freed !).
a5a9f428	119	*
2f10494a MD	120	* uatomic_cmpxchg() acts as both release and acquire barriers.
2f10494a MD	121	*
a5a9f428 PM	122	* This macro is less than 10 lines long. The intent is that this macro
	123	* meets the 10-line criterion in LGPL, allowing this function to be
	124	* expanded directly in non-LGPL code.
7e30abe3	125	*/
2b5554c9	126	#define _rcu_cmpxchg_pointer(p, old, _new) \
1b85da85	127	__extension__ \
2b5554c9	128	({ \
bdffa73a MD	129	__typeof__(*p) _________pold = (old); \
bdffa73a MD	130	__typeof__(*p) _________pnew = (_new); \
bf9de1b7	131	uatomic_cmpxchg(p, _________pold, _________pnew); \
7e30abe3 MD	132	})
	133
	134	/**
	135	* _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
	136	* pointer to the data structure, which can be safely freed after waiting for a
	137	* quiescent state using synchronize_rcu().
a5a9f428	138	*
2f10494a MD	139	* uatomic_xchg() acts as both release and acquire barriers.
2f10494a MD	140	*
a5a9f428 PM	141	* This macro is less than 10 lines long. The intent is that this macro
	142	* meets the 10-line criterion in LGPL, allowing this function to be
	143	* expanded directly in non-LGPL code.
7e30abe3	144	*/
7e30abe3	145	#define _rcu_xchg_pointer(p, v) \
1b85da85	146	__extension__ \
7e30abe3	147	({ \
bdffa73a	148	__typeof__(*p) _________pv = (v); \
2b5554c9	149	uatomic_xchg(p, _________pv); \
7e30abe3 MD	150	})
	151
	152
	153	#define _rcu_set_pointer(p, v) \
3daae22a	154	do { \
bdffa73a	155	__typeof__(*p) _________pv = (v); \
7e30abe3 MD	156	if (!__builtin_constant_p(v) \|\| \
7e30abe3 MD	157	((v) != NULL)) \
5481ddb3	158	cmm_wmb(); \
bf9de1b7	159	uatomic_set(p, _________pv); \
3daae22a	160	} while (0)
7e30abe3	161
7e30abe3 MD	162	/**
	163	* _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
	164	* meant to be read by RCU read-side critical sections. Returns the assigned
	165	* value.
	166	*
	167	* Documents which pointers will be dereferenced by RCU read-side critical
	168	* sections and adds the required memory barriers on architectures requiring
	169	* them. It also makes sure the compiler does not reorder code initializing the
	170	* data structure before its publication.
	171	*
edf8de69	172	* Should match rcu_dereference().
a5a9f428 PM	173	*
	174	* This macro is less than 10 lines long. The intent is that this macro
	175	* meets the 10-line criterion in LGPL, allowing this function to be
	176	* expanded directly in non-LGPL code.
7e30abe3	177	*/
7e30abe3 MD	178	#define _rcu_assign_pointer(p, v) _rcu_set_pointer(&(p), v)
7e30abe3 MD	179
67ecffc0	180	#ifdef __cplusplus
36bc70a8 MD	181	}
	182	#endif
	183
7e30abe3	184	#endif /* _URCU_POINTER_STATIC_H */