[urcu.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 <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

#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 CONFIG_URCU_AVOID_SIGNALS are much slower. Account this in
 * the delay.
 */
#ifdef CONFIG_URCU_AVOID_SIGNALS
/* 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 CONFIG_URCU_AVOID_SIGNALS
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)

/*
 * 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;

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