Atomic Operations
[Apache Portability Runtime library]

Functions
apr_status_t	apr_atomic_init (apr_pool_t *p)
apr_uint32_t	apr_atomic_read32 (volatile apr_uint32_t *mem)
void	apr_atomic_set32 (volatile apr_uint32_t *mem, apr_uint32_t val)
apr_uint32_t	apr_atomic_add32 (volatile apr_uint32_t *mem, apr_uint32_t val)
void	apr_atomic_sub32 (volatile apr_uint32_t *mem, apr_uint32_t val)
apr_uint32_t	apr_atomic_inc32 (volatile apr_uint32_t *mem)
int	apr_atomic_dec32 (volatile apr_uint32_t *mem)
apr_uint32_t	apr_atomic_cas32 (volatile apr_uint32_t *mem, apr_uint32_t with, apr_uint32_t cmp)
apr_uint32_t	apr_atomic_xchg32 (volatile apr_uint32_t *mem, apr_uint32_t val)
void *	apr_atomic_casptr (volatile void **mem, void *with, const void *cmp)
void *	apr_atomic_xchgptr (volatile void **mem, void *with)

---

Function Documentation

apr_uint32_t apr_atomic_add32	(	volatile apr_uint32_t *	mem,
		apr_uint32_t	val
	)

atomically add 'val' to an apr_uint32_t

Parameters:

	mem	pointer to the object
	val	amount to add

Returns:

old value pointed to by mem

apr_uint32_t apr_atomic_cas32	(	volatile apr_uint32_t *	mem,
		apr_uint32_t	with,
		apr_uint32_t	cmp
	)

compare an apr_uint32_t's value with 'cmp'. If they are the same swap the value with 'with'

Parameters:

	mem	pointer to the value
	with	what to swap it with
	cmp	the value to compare it to

Returns:

the old value of *mem

void* apr_atomic_casptr	(	volatile void **	mem,
		void *	with,
		const void *	cmp
	)

compare the pointer's value with cmp. If they are the same swap the value with 'with'

Parameters:

	mem	pointer to the pointer
	with	what to swap it with
	cmp	the value to compare it to

Returns:

the old value of the pointer

int apr_atomic_dec32

(

volatile apr_uint32_t *

mem

)

atomically decrement an apr_uint32_t by 1

Parameters:

mem

pointer to the atomic value

Returns:

zero if the value becomes zero on decrement, otherwise non-zero

apr_uint32_t apr_atomic_inc32

(

volatile apr_uint32_t *

mem

)

atomically increment an apr_uint32_t by 1

Parameters:

mem

pointer to the object

Returns:

old value pointed to by mem

apr_status_t apr_atomic_init

(

apr_pool_t *

p

)

this function is required on some platforms to initialize the atomic operation's internal structures

Parameters:

p

pool

Returns:

APR_SUCCESS on successful completion

Remarks:

Programs do NOT need to call this directly. APR will call this automatically from apr_initialize.

apr_uint32_t apr_atomic_read32

(

volatile apr_uint32_t *

mem

)

atomically read an apr_uint32_t from memory

Parameters:

mem

the pointer

void apr_atomic_set32	(	volatile apr_uint32_t *	mem,
		apr_uint32_t	val
	)

atomically set an apr_uint32_t in memory

Parameters:

	mem	pointer to the object
	val	value that the object will assume

void apr_atomic_sub32	(	volatile apr_uint32_t *	mem,
		apr_uint32_t	val
	)

atomically subtract 'val' from an apr_uint32_t

Parameters:

	mem	pointer to the object
	val	amount to subtract

apr_uint32_t apr_atomic_xchg32	(	volatile apr_uint32_t *	mem,
		apr_uint32_t	val
	)

exchange an apr_uint32_t's value with 'val'.

Parameters:

	mem	pointer to the value
	val	what to swap it with

Returns:

the old value of *mem

void* apr_atomic_xchgptr	(	volatile void **	mem,
		void *	with
	)

exchange a pair of pointer values

Parameters:

	mem	pointer to the pointer
	with	what to swap it with

Returns:

the old value of the pointer