[urcu.git] / urcu.h

#ifndef _URCU_H
#define _URCU_H

/*
 * urcu.h
 *
 * Userspace RCU header
 *
 * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
 *
 * Credits for Paul e. McKenney <paulmck@linux.vnet.ibm.com>
 * for inspiration coming from the Linux kernel RCU and rcu-preempt.
 *
 * The barrier, mb, rmb, wmb, atomic_inc, smp_read_barrier_depends, ACCESS_ONCE
 * and rcu_dereference primitives come from the Linux kernel.
 *
 * 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")

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_unregister_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	*
5e7e64b9 MD	11	* Credits for Paul e. McKenney <paulmck@linux.vnet.ibm.com>
	12	* for inspiration coming from the Linux kernel RCU and rcu-preempt.
	13	*
	14	* The barrier, mb, rmb, wmb, atomic_inc, smp_read_barrier_depends, ACCESS_ONCE
	15	* and rcu_dereference primitives come from the Linux kernel.
	16	*
b257a10b MD	17	* Distributed under GPLv2
	18	*/
	19
27b012e2 MD	20	/* The "volatile" is due to gcc bugs */
	21	#define barrier() __asm__ __volatile__("": : :"memory")
	22
	23	/* x86 32/64 specific */
	24	#define mb() asm volatile("mfence":::"memory")
	25	#define rmb() asm volatile("lfence":::"memory")
	26	#define wmb() asm volatile("sfence" ::: "memory")
	27
27b012e2 MD	28	static inline void atomic_inc(int *v)
	29	{
	30	asm volatile("lock; incl %0"
f69f195a	31	: "+m" (*v));
27b012e2 MD	32	}
	33
	34	/* Nop everywhere except on alpha. */
	35	#define smp_read_barrier_depends()
	36
41718ff9 MD	37	/*
	38	* Prevent the compiler from merging or refetching accesses. The compiler
	39	* is also forbidden from reordering successive instances of ACCESS_ONCE(),
	40	* but only when the compiler is aware of some particular ordering. One way
	41	* to make the compiler aware of ordering is to put the two invocations of
	42	* ACCESS_ONCE() in different C statements.
	43	*
	44	* This macro does absolutely -nothing- to prevent the CPU from reordering,
	45	* merging, or refetching absolutely anything at any time. Its main intended
	46	* use is to mediate communication between process-level code and irq/NMI
	47	* handlers, all running on the same CPU.
	48	*/
	49	#define ACCESS_ONCE(x) ((volatile typeof(x) )&(x))
	50
	51	/**
	52	* rcu_dereference - fetch an RCU-protected pointer in an
	53	* RCU read-side critical section. This pointer may later
	54	* be safely dereferenced.
	55	*
	56	* Inserts memory barriers on architectures that require them
	57	* (currently only the Alpha), and, more importantly, documents
	58	* exactly which pointers are protected by RCU.
	59	*/
	60
	61	#define rcu_dereference(p) ({ \
	62	typeof(p) _________p1 = ACCESS_ONCE(p); \
	63	smp_read_barrier_depends(); \
	64	(_________p1); \
	65	})
	66
27b012e2 MD	67	#define SIGURCU SIGUSR1
	68
	69	/* Global quiescent period parity */
	70	extern int urcu_qparity;
	71
	72	extern int __thread urcu_active_readers[2];
	73
	74	static inline int get_urcu_qparity(void)
	75	{
	76	return urcu_qparity;
	77	}
	78
	79	/*
	80	* returns urcu_parity.
	81	*/
	82	static inline int rcu_read_lock(void)
	83	{
	84	int urcu_parity = get_urcu_qparity();
	85	urcu_active_readers[urcu_parity]++;
	86	/*
	87	* Increment active readers count before accessing the pointer.
	88	* See force_mb_all_threads().
	89	*/
	90	barrier();
	91	return urcu_parity;
	92	}
	93
	94	static inline void rcu_read_unlock(int urcu_parity)
	95	{
	96	barrier();
	97	/*
	98	* Finish using rcu before decrementing the pointer.
	99	* See force_mb_all_threads().
	100	*/
	101	urcu_active_readers[urcu_parity]--;
	102	}
	103
41718ff9 MD	104	extern void rcu_write_lock(void);
	105	extern void rcu_write_unlock(void);
	106
cdcb92bb	107	extern void urcu_publish_content(void ptr, void new);
27b012e2 MD	108
	109	/*
	110	* Reader thread registration.
	111	*/
	112	extern void urcu_register_thread(void);
5e7e64b9	113	extern void urcu_unregister_thread(void);
27b012e2 MD	114
27b012e2 MD	115	#endif /* _URCU_H */