[urcu.git] / urcu.h

#ifndef _URCU_H
#define _URCU_H

/*
 * urcu.h
 *
 * Userspace RCU header
 *
 * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
 *
 * Distributed under GPLv2
 */

/* The "volatile" is due to gcc bugs */
#define barrier() __asm__ __volatile__("": : :"memory")

/* x86 32/64 specific */
#define mb()    asm volatile("mfence":::"memory")
#define rmb()   asm volatile("lfence":::"memory")
#define wmb()   asm volatile("sfence" ::: "memory")


/* x86 32 */
static inline void atomic_inc(int *v)
{
	asm volatile("lock; incl %0"
		     : "+m" (*v));
}

/* Nop everywhere except on alpha. */
#define smp_read_barrier_depends()

/*
 * Prevent the compiler from merging or refetching accesses.  The compiler
 * is also forbidden from reordering successive instances of ACCESS_ONCE(),
 * but only when the compiler is aware of some particular ordering.  One way
 * to make the compiler aware of ordering is to put the two invocations of
 * ACCESS_ONCE() in different C statements.
 *
 * This macro does absolutely -nothing- to prevent the CPU from reordering,
 * merging, or refetching absolutely anything at any time.  Its main intended
 * use is to mediate communication between process-level code and irq/NMI
 * handlers, all running on the same CPU.
 */
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))

/**
 * rcu_dereference - fetch an RCU-protected pointer in an
 * RCU read-side critical section.  This pointer may later
 * be safely dereferenced.
 *
 * Inserts memory barriers on architectures that require them
 * (currently only the Alpha), and, more importantly, documents
 * exactly which pointers are protected by RCU.
 */

#define rcu_dereference(p)     ({ \
				typeof(p) _________p1 = ACCESS_ONCE(p); \
				smp_read_barrier_depends(); \
				(_________p1); \
				})

#define SIGURCU SIGUSR1

/* Global quiescent period parity */
extern int urcu_qparity;

extern int __thread urcu_active_readers[2];

static inline int get_urcu_qparity(void)
{
	return urcu_qparity;
}

/*
 * returns urcu_parity.
 */
static inline int rcu_read_lock(void)
{
	int urcu_parity = get_urcu_qparity();
	urcu_active_readers[urcu_parity]++;
	/*
	 * Increment active readers count before accessing the pointer.
	 * See force_mb_all_threads().
	 */
	barrier();
	return urcu_parity;
}

static inline void rcu_read_unlock(int urcu_parity)
{
	barrier();
	/*
	 * Finish using rcu before decrementing the pointer.
	 * See force_mb_all_threads().
	 */
	urcu_active_readers[urcu_parity]--;
}

extern void rcu_write_lock(void);
extern void rcu_write_unlock(void);

extern void *urcu_publish_content(void **ptr, void *new);

/*
 * Reader thread registration.
 */
extern void urcu_register_thread(void);
extern void urcu_register_thread(void);

#endif /* _URCU_H */
Commit	Line	Data
27b012e2 MD	1	#ifndef _URCU_H
	2	#define _URCU_H
	3
b257a10b MD	4	/*
	5	* urcu.h
	6	*
	7	* Userspace RCU header
	8	*
	9	* Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
	10	*
	11	* Distributed under GPLv2
	12	*/
	13
27b012e2 MD	14	/* The "volatile" is due to gcc bugs */
	15	#define barrier() __asm__ __volatile__("": : :"memory")
	16
	17	/* x86 32/64 specific */
	18	#define mb() asm volatile("mfence":::"memory")
	19	#define rmb() asm volatile("lfence":::"memory")
	20	#define wmb() asm volatile("sfence" ::: "memory")
	21
	22
	23
	24	/* x86 32 */
	25	static inline void atomic_inc(int *v)
	26	{
	27	asm volatile("lock; incl %0"
f69f195a	28	: "+m" (*v));
27b012e2 MD	29	}
	30
	31	/* Nop everywhere except on alpha. */
	32	#define smp_read_barrier_depends()
	33
41718ff9 MD	34	/*
	35	* Prevent the compiler from merging or refetching accesses. The compiler
	36	* is also forbidden from reordering successive instances of ACCESS_ONCE(),
	37	* but only when the compiler is aware of some particular ordering. One way
	38	* to make the compiler aware of ordering is to put the two invocations of
	39	* ACCESS_ONCE() in different C statements.
	40	*
	41	* This macro does absolutely -nothing- to prevent the CPU from reordering,
	42	* merging, or refetching absolutely anything at any time. Its main intended
	43	* use is to mediate communication between process-level code and irq/NMI
	44	* handlers, all running on the same CPU.
	45	*/
	46	#define ACCESS_ONCE(x) ((volatile typeof(x) )&(x))
	47
	48	/**
	49	* rcu_dereference - fetch an RCU-protected pointer in an
	50	* RCU read-side critical section. This pointer may later
	51	* be safely dereferenced.
	52	*
	53	* Inserts memory barriers on architectures that require them
	54	* (currently only the Alpha), and, more importantly, documents
	55	* exactly which pointers are protected by RCU.
	56	*/
	57
	58	#define rcu_dereference(p) ({ \
	59	typeof(p) _________p1 = ACCESS_ONCE(p); \
	60	smp_read_barrier_depends(); \
	61	(_________p1); \
	62	})
	63
27b012e2 MD	64	#define SIGURCU SIGUSR1
	65
	66	/* Global quiescent period parity */
	67	extern int urcu_qparity;
	68
	69	extern int __thread urcu_active_readers[2];
	70
	71	static inline int get_urcu_qparity(void)
	72	{
	73	return urcu_qparity;
	74	}
	75
	76	/*
	77	* returns urcu_parity.
	78	*/
	79	static inline int rcu_read_lock(void)
	80	{
	81	int urcu_parity = get_urcu_qparity();
	82	urcu_active_readers[urcu_parity]++;
	83	/*
	84	* Increment active readers count before accessing the pointer.
	85	* See force_mb_all_threads().
	86	*/
	87	barrier();
	88	return urcu_parity;
	89	}
	90
	91	static inline void rcu_read_unlock(int urcu_parity)
	92	{
	93	barrier();
	94	/*
	95	* Finish using rcu before decrementing the pointer.
	96	* See force_mb_all_threads().
	97	*/
	98	urcu_active_readers[urcu_parity]--;
	99	}
	100
41718ff9 MD	101	extern void rcu_write_lock(void);
	102	extern void rcu_write_unlock(void);
	103
27b012e2 MD	104	extern void urcu_publish_content(void ptr, void new);
	105
	106	/*
	107	* Reader thread registration.
	108	*/
	109	extern void urcu_register_thread(void);
	110	extern void urcu_register_thread(void);
	111
	112	#endif /* _URCU_H */