[userspace-rcu.git] / urcu-static.h

#ifndef _URCU_STATIC_H
#define _URCU_STATIC_H

/*
 * urcu-static.h
 *
 * Userspace RCU header.
 *
 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
 * dynamically with the userspace rcu library.
 *
 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
 * 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 <stdlib.h>
#include <pthread.h>
#include <sched.h>

#include <compiler.h>
#include <arch.h>

/*
 * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
 */
#define _LOAD_SHARED(p)	       ACCESS_ONCE(p)

/*
 * Load a data from shared memory, doing a cache flush if required.
 */
#define LOAD_SHARED(p)			\
	({				\
		smp_rmc();		\
		_LOAD_SHARED(p);	\
	})

/*
 * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
 */
#define _STORE_SHARED(x, v)	({ ACCESS_ONCE(x) = (v); })

/*
 * Store v into x, where x is located in shared memory. Performs the required
 * cache flush after writing. Returns v.
 */
#define STORE_SHARED(x, v)		\
	({				\
		_STORE_SHARED(x, v);	\
		smp_wmc();		\
		(v);			\
	})

/**
 * _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 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().
 */

#define _rcu_dereference(p)     ({					\
				typeof(p) _________p1 = LOAD_SHARED(p); \
				smp_read_barrier_depends();		\
				(_________p1);				\
				})

/*
 * This code section can only be included in LGPL 2.1 compatible source code.
 * See below for the function call wrappers which can be used in code meant to
 * be only linked with the Userspace RCU library. This comes with a small
 * performance degradation on the read-side due to the added function calls.
 * This is required to permit relinking with newer versions of the library.
 */

/*
 * The signal number used by the RCU library can be overridden with
 * -DSIGURCU= when compiling the library.
 */
#ifndef SIGURCU
#define SIGURCU SIGUSR1
#endif

/*
 * If a reader is really non-cooperative and refuses to commit its
 * urcu_active_readers count to memory (there is no barrier in the reader
 * per-se), kick it after a few loops waiting for it.
 */
#define KICK_READER_LOOPS 10000

/*
 * Active attempts to check for reader Q.S. before calling sched_yield().
 */
#define RCU_QS_ACTIVE_ATTEMPTS 100

#ifdef DEBUG_RCU
#define rcu_assert(args...)	assert(args)
#else
#define rcu_assert(args...)
#endif

#ifdef DEBUG_YIELD
#include <sched.h>
#include <time.h>
#include <pthread.h>
#include <unistd.h>

#define YIELD_READ 	(1 << 0)
#define YIELD_WRITE	(1 << 1)

/*
 * Updates without URCU_MB are much slower. Account this in
 * the delay.
 */
#ifdef URCU_MB
/* maximum sleep delay, in us */
#define MAX_SLEEP 50
#else
#define MAX_SLEEP 30000
#endif

extern unsigned int yield_active;
extern unsigned int __thread rand_yield;

static inline void debug_yield_read(void)
{
	if (yield_active & YIELD_READ)
		if (rand_r(&rand_yield) & 0x1)
			usleep(rand_r(&rand_yield) % MAX_SLEEP);
}

static inline void debug_yield_write(void)
{
	if (yield_active & YIELD_WRITE)
		if (rand_r(&rand_yield) & 0x1)
			usleep(rand_r(&rand_yield) % MAX_SLEEP);
}

static inline void debug_yield_init(void)
{
	rand_yield = time(NULL) ^ pthread_self();
}
#else
static inline void debug_yield_read(void)
{
}

static inline void debug_yield_write(void)
{
}

static inline void debug_yield_init(void)
{

}
#endif

#ifdef URCU_MB
static inline void reader_barrier()
{
	smp_mb();
}
#else
static inline void reader_barrier()
{
	barrier();
}
#endif

/*
 * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 */
#define RCU_GP_COUNT		(1UL << 0)
/* Use the amount of bits equal to half of the architecture long size */
#define RCU_GP_CTR_BIT		(1UL << (sizeof(long) << 2))
#define RCU_GP_CTR_NEST_MASK	(RCU_GP_CTR_BIT - 1)
#define RCU_GP_ONGOING		(RCU_GP_CTR_BIT << 1)

/*
 * Global quiescent period counter with low-order bits unused.
 * Using a int rather than a char to eliminate false register dependencies
 * causing stalls on some architectures.
 */
extern long urcu_gp_ctr;

extern long __thread urcu_active_readers;

static inline int rcu_old_gp_ongoing(long *value)
{
	long v;

	if (value == NULL)
		return 0;
	/*
	 * Make sure both tests below are done on the same version of *value
	 * to insure consistency.
	 */
	v = LOAD_SHARED(*value);
	return (v & RCU_GP_CTR_NEST_MASK) &&
		 ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
}

static inline void _rcu_read_lock(void)
{
	long tmp, gp_ctr;

	tmp = urcu_active_readers;
	/* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
	if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
		gp_ctr = _LOAD_SHARED(urcu_gp_ctr);
		if (unlikely(gp_ctr & RCU_GP_ONGOING)) {
			sched_yield();
			gp_ctr = _LOAD_SHARED(urcu_gp_ctr);
		}
		_STORE_SHARED(urcu_active_readers, gp_ctr);
		/*
		 * Set active readers count for outermost nesting level before
		 * accessing the pointer. See force_mb_all_threads().
		 */
		reader_barrier();
	} else {
		_STORE_SHARED(urcu_active_readers, tmp + RCU_GP_COUNT);
	}
}

static inline void _rcu_read_unlock(void)
{
	/*
	 * Finish using rcu before decrementing the pointer.
	 * See force_mb_all_threads().
	 * Formally only needed for outermost nesting level, but leave barrier
	 * in place for nested unlocks to remove a branch from the common case
	 * (no nesting).
	 */
	reader_barrier();
	_STORE_SHARED(urcu_active_readers, urcu_active_readers - RCU_GP_COUNT);
}

/**
 * _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_pointer().
 */

#define _rcu_assign_pointer(p, v)			\
	({						\
		if (!__builtin_constant_p(v) || 	\
		    ((v) != NULL))			\
			wmb();				\
		STORE_SHARED(p, v);			\
	})

/**
 * _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 !).
 */

#define _rcu_cmpxchg_pointer(p, old, _new)		\
	({						\
		if (!__builtin_constant_p(_new) ||	\
		    ((_new) != NULL))			\
			wmb();				\
		cmpxchg(p, old, _new);			\
	})

/**
 * _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().
 */

#define _rcu_xchg_pointer(p, v)				\
	({						\
		if (!__builtin_constant_p(v) ||		\
		    ((v) != NULL))			\
			wmb();				\
		xchg(p, v);				\
	})

/*
 * Exchanges the pointer and waits for quiescent state.
 * The pointer returned can be freed.
 */
#define _rcu_publish_content(p, v)			\
	({						\
		void *oldptr;				\
		oldptr = _rcu_xchg_pointer(p, v);	\
		synchronize_rcu();			\
		oldptr;					\
	})

#endif /* _URCU_STATIC_H */
Commit	Line	Data
adcfce54 MD	1	#ifndef _URCU_STATIC_H
	2	#define _URCU_STATIC_H
	3
	4	/*
	5	* urcu-static.h
	6	*
d2d23035	7	* Userspace RCU header.
adcfce54	8	*
d2d23035 MD	9	* TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
d2d23035 MD	10	* dynamically with the userspace rcu library.
adcfce54	11	*
d2d23035 MD	12	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
d2d23035 MD	13	* Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
adcfce54	14	*
d2d23035 MD	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
adcfce54 MD	28	*
	29	* IBM's contributions to this file may be relicensed under LGPLv2 or later.
	30	*/
	31
	32	#include <stdlib.h>
	33	#include <pthread.h>
ae62b5e8	34	#include <sched.h>
adcfce54 MD	35
	36	#include <compiler.h>
	37	#include <arch.h>
	38
	39	/*
	40	* Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
	41	*/
	42	#define _LOAD_SHARED(p) ACCESS_ONCE(p)
	43
	44	/*
	45	* Load a data from shared memory, doing a cache flush if required.
	46	*/
	47	#define LOAD_SHARED(p) \
	48	({ \
	49	smp_rmc(); \
	50	_LOAD_SHARED(p); \
	51	})
	52
	53	/*
	54	* Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
	55	*/
	56	#define _STORE_SHARED(x, v) ({ ACCESS_ONCE(x) = (v); })
	57
	58	/*
	59	* Store v into x, where x is located in shared memory. Performs the required
	60	* cache flush after writing. Returns v.
	61	*/
	62	#define STORE_SHARED(x, v) \
	63	({ \
	64	_STORE_SHARED(x, v); \
	65	smp_wmc(); \
	66	(v); \
	67	})
	68
	69	/**
	70	* _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
	71	* into a RCU read-side critical section. The pointer can later be safely
	72	* dereferenced within the critical section.
	73	*
	74	* This ensures that the pointer copy is invariant thorough the whole critical
	75	* section.
	76	*
	77	* Inserts memory barriers on architectures that require them (currently only
	78	* Alpha) and documents which pointers are protected by RCU.
	79	*
809f4fde MD	80	* The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
	81	* optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
	82	* data read before the pointer read by speculating the value of the pointer.
	83	* Correct ordering is ensured because the pointer is read as a volatile access.
	84	* This acts as a global side-effect operation, which forbids reordering of
015c702f MD	85	* dependent memory operations. Note that such concern about dependency-breaking
	86	* optimizations will eventually be taken care of by the "memory_order_consume"
	87	* addition to forthcoming C++ standard.
809f4fde	88	*
adcfce54 MD	89	* Should match rcu_assign_pointer() or rcu_xchg_pointer().
	90	*/
	91
	92	#define _rcu_dereference(p) ({ \
	93	typeof(p) _________p1 = LOAD_SHARED(p); \
	94	smp_read_barrier_depends(); \
	95	(_________p1); \
	96	})
	97
	98	/*
	99	* This code section can only be included in LGPL 2.1 compatible source code.
	100	* See below for the function call wrappers which can be used in code meant to
	101	* be only linked with the Userspace RCU library. This comes with a small
	102	* performance degradation on the read-side due to the added function calls.
	103	* This is required to permit relinking with newer versions of the library.
	104	*/
	105
	106	/*
	107	* The signal number used by the RCU library can be overridden with
	108	* -DSIGURCU= when compiling the library.
	109	*/
	110	#ifndef SIGURCU
	111	#define SIGURCU SIGUSR1
	112	#endif
	113
	114	/*
	115	* If a reader is really non-cooperative and refuses to commit its
	116	* urcu_active_readers count to memory (there is no barrier in the reader
	117	* per-se), kick it after a few loops waiting for it.
	118	*/
	119	#define KICK_READER_LOOPS 10000
	120
bc6c15bb	121	/*
ae62b5e8	122	* Active attempts to check for reader Q.S. before calling sched_yield().
bc6c15bb MD	123	*/
	124	#define RCU_QS_ACTIVE_ATTEMPTS 100
	125
7ac06cef MD	126	#ifdef DEBUG_RCU
	127	#define rcu_assert(args...) assert(args)
	128	#else
	129	#define rcu_assert(args...)
	130	#endif
	131
adcfce54 MD	132	#ifdef DEBUG_YIELD
	133	#include <sched.h>
	134	#include <time.h>
	135	#include <pthread.h>
	136	#include <unistd.h>
	137
	138	#define YIELD_READ (1 << 0)
	139	#define YIELD_WRITE (1 << 1)
	140
b4ce1526	141	/*
0a1d290b	142	* Updates without URCU_MB are much slower. Account this in
b4ce1526 MD	143	* the delay.
b4ce1526 MD	144	*/
0a1d290b	145	#ifdef URCU_MB
adcfce54 MD	146	/* maximum sleep delay, in us */
	147	#define MAX_SLEEP 50
	148	#else
	149	#define MAX_SLEEP 30000
	150	#endif
	151
	152	extern unsigned int yield_active;
	153	extern unsigned int __thread rand_yield;
	154
	155	static inline void debug_yield_read(void)
	156	{
	157	if (yield_active & YIELD_READ)
	158	if (rand_r(&rand_yield) & 0x1)
	159	usleep(rand_r(&rand_yield) % MAX_SLEEP);
	160	}
	161
	162	static inline void debug_yield_write(void)
	163	{
	164	if (yield_active & YIELD_WRITE)
	165	if (rand_r(&rand_yield) & 0x1)
	166	usleep(rand_r(&rand_yield) % MAX_SLEEP);
	167	}
	168
	169	static inline void debug_yield_init(void)
	170	{
	171	rand_yield = time(NULL) ^ pthread_self();
	172	}
	173	#else
	174	static inline void debug_yield_read(void)
	175	{
	176	}
	177
	178	static inline void debug_yield_write(void)
	179	{
	180	}
	181
	182	static inline void debug_yield_init(void)
	183	{
	184
	185	}
	186	#endif
	187
0a1d290b	188	#ifdef URCU_MB
adcfce54 MD	189	static inline void reader_barrier()
	190	{
	191	smp_mb();
	192	}
	193	#else
	194	static inline void reader_barrier()
	195	{
	196	barrier();
	197	}
	198	#endif
	199
	200	/*
	201	* The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
	202	* full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
	203	*/
	204	#define RCU_GP_COUNT (1UL << 0)
	205	/* Use the amount of bits equal to half of the architecture long size */
	206	#define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
	207	#define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
ae62b5e8	208	#define RCU_GP_ONGOING (RCU_GP_CTR_BIT << 1)
adcfce54 MD	209
	210	/*
	211	* Global quiescent period counter with low-order bits unused.
	212	* Using a int rather than a char to eliminate false register dependencies
	213	* causing stalls on some architectures.
	214	*/
	215	extern long urcu_gp_ctr;
	216
	217	extern long __thread urcu_active_readers;
	218
	219	static inline int rcu_old_gp_ongoing(long *value)
	220	{
	221	long v;
	222
	223	if (value == NULL)
	224	return 0;
	225	/*
	226	* Make sure both tests below are done on the same version of *value
	227	* to insure consistency.
	228	*/
	229	v = LOAD_SHARED(*value);
	230	return (v & RCU_GP_CTR_NEST_MASK) &&
	231	((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
	232	}
	233
	234	static inline void _rcu_read_lock(void)
	235	{
ae62b5e8	236	long tmp, gp_ctr;
adcfce54 MD	237
	238	tmp = urcu_active_readers;
	239	/* urcu_gp_ctr = RCU_GP_COUNT \| (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
67ef1a2c	240	if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
ae62b5e8 MD	241	gp_ctr = _LOAD_SHARED(urcu_gp_ctr);
	242	if (unlikely(gp_ctr & RCU_GP_ONGOING)) {
	243	sched_yield();
	244	gp_ctr = _LOAD_SHARED(urcu_gp_ctr);
	245	}
	246	_STORE_SHARED(urcu_active_readers, gp_ctr);
67ef1a2c MD	247	/*
	248	* Set active readers count for outermost nesting level before
	249	* accessing the pointer. See force_mb_all_threads().
	250	*/
	251	reader_barrier();
	252	} else {
adcfce54	253	_STORE_SHARED(urcu_active_readers, tmp + RCU_GP_COUNT);
67ef1a2c	254	}
adcfce54 MD	255	}
	256
	257	static inline void _rcu_read_unlock(void)
	258	{
adcfce54 MD	259	/*
	260	* Finish using rcu before decrementing the pointer.
	261	* See force_mb_all_threads().
ae62b5e8 MD	262	* Formally only needed for outermost nesting level, but leave barrier
	263	* in place for nested unlocks to remove a branch from the common case
	264	* (no nesting).
adcfce54	265	*/
ae62b5e8 MD	266	reader_barrier();
ae62b5e8 MD	267	_STORE_SHARED(urcu_active_readers, urcu_active_readers - RCU_GP_COUNT);
adcfce54 MD	268	}
	269
	270	/**
	271	* _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
	272	* meant to be read by RCU read-side critical sections. Returns the assigned
	273	* value.
	274	*
	275	* Documents which pointers will be dereferenced by RCU read-side critical
	276	* sections and adds the required memory barriers on architectures requiring
	277	* them. It also makes sure the compiler does not reorder code initializing the
	278	* data structure before its publication.
	279	*
	280	* Should match rcu_dereference_pointer().
	281	*/
	282
	283	#define _rcu_assign_pointer(p, v) \
	284	({ \
	285	if (!__builtin_constant_p(v) \|\| \
	286	((v) != NULL)) \
	287	wmb(); \
	288	STORE_SHARED(p, v); \
	289	})
	290
4d1ce26f MD	291	/**
	292	* _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
	293	* is as expected by "old". If succeeds, returns the previous pointer to the
	294	* data structure, which can be safely freed after waiting for a quiescent state
	295	* using synchronize_rcu(). If fails (unexpected value), returns old (which
	296	* should not be freed !).
	297	*/
	298
	299	#define _rcu_cmpxchg_pointer(p, old, _new) \
	300	({ \
	301	if (!__builtin_constant_p(_new) \|\| \
	302	((_new) != NULL)) \
	303	wmb(); \
	304	cmpxchg(p, old, _new); \
	305	})
	306
adcfce54 MD	307	/**
adcfce54 MD	308	* _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
67ef1a2c	309	* pointer to the data structure, which can be safely freed after waiting for a
adcfce54 MD	310	* quiescent state using synchronize_rcu().
	311	*/
	312
	313	#define _rcu_xchg_pointer(p, v) \
	314	({ \
	315	if (!__builtin_constant_p(v) \|\| \
	316	((v) != NULL)) \
	317	wmb(); \
	318	xchg(p, v); \
	319	})
	320
	321	/*
	322	* Exchanges the pointer and waits for quiescent state.
	323	* The pointer returned can be freed.
	324	*/
	325	#define _rcu_publish_content(p, v) \
	326	({ \
	327	void *oldptr; \
	328	oldptr = _rcu_xchg_pointer(p, v); \
	329	synchronize_rcu(); \
	330	oldptr; \
	331	})
	332
	333	#endif /* _URCU_STATIC_H */