Skip list implementation

Typedefs
typedef int(*	apr_skiplist_compare) (void *, void *)
typedef void(*	apr_skiplist_freefunc) (void *)
typedef struct apr_skiplist	apr_skiplist
typedef struct apr_skiplistnode	apr_skiplistnode

Functions
void *	apr_skiplist_alloc (apr_skiplist *sl, size_t size)
void	apr_skiplist_free (apr_skiplist *sl, void *mem)
apr_status_t	apr_skiplist_init (apr_skiplist **sl, apr_pool_t *p)
void	apr_skiplist_set_compare (apr_skiplist *sl, apr_skiplist_compare XXX1, apr_skiplist_compare XXX2)
void	apr_skiplist_add_index (apr_skiplist *sl, apr_skiplist_compare XXX1, apr_skiplist_compare XXX2)
apr_skiplistnode *	apr_skiplist_getlist (apr_skiplist *sl)
void *	apr_skiplist_find_compare (apr_skiplist *sl, void *data, apr_skiplistnode **iter, apr_skiplist_compare func)
void *	apr_skiplist_find (apr_skiplist *sl, void *data, apr_skiplistnode **iter)
void *	apr_skiplist_last_compare (apr_skiplist *sl, void *data, apr_skiplistnode **iter, apr_skiplist_compare comp)
void *	apr_skiplist_last (apr_skiplist *sl, void *data, apr_skiplistnode **iter)
void *	apr_skiplist_next (apr_skiplist *sl, apr_skiplistnode **iter)
void *	apr_skiplist_previous (apr_skiplist *sl, apr_skiplistnode **iter)
void *	apr_skiplist_element (apr_skiplistnode *iter)
apr_skiplistnode *	apr_skiplist_insert_compare (apr_skiplist *sl, void *data, apr_skiplist_compare comp)
apr_skiplistnode *	apr_skiplist_insert (apr_skiplist *sl, void *data)
apr_skiplistnode *	apr_skiplist_add_compare (apr_skiplist *sl, void *data, apr_skiplist_compare comp)
apr_skiplistnode *	apr_skiplist_add (apr_skiplist *sl, void *data)
apr_skiplistnode *	apr_skiplist_replace_compare (apr_skiplist *sl, void *data, apr_skiplist_freefunc myfree, apr_skiplist_compare comp)
apr_skiplistnode *	apr_skiplist_replace (apr_skiplist *sl, void *data, apr_skiplist_freefunc myfree)
int	apr_skiplist_remove_node (apr_skiplist *sl, apr_skiplistnode *iter, apr_skiplist_freefunc myfree)
int	apr_skiplist_remove_compare (apr_skiplist *sl, void *data, apr_skiplist_freefunc myfree, apr_skiplist_compare comp)
int	apr_skiplist_remove (apr_skiplist *sl, void *data, apr_skiplist_freefunc myfree)
void	apr_skiplist_remove_all (apr_skiplist *sl, apr_skiplist_freefunc myfree)
void	apr_skiplist_destroy (apr_skiplist *sl, apr_skiplist_freefunc myfree)
void *	apr_skiplist_pop (apr_skiplist *sl, apr_skiplist_freefunc myfree)
void *	apr_skiplist_peek (apr_skiplist *sl)
size_t	apr_skiplist_size (const apr_skiplist *sl)
int	apr_skiplist_height (const apr_skiplist *sl)
int	apr_skiplist_preheight (const apr_skiplist *sl)
void	apr_skiplist_set_preheight (apr_skiplist *sl, int to)
apr_skiplist *	apr_skiplist_merge (apr_skiplist *sl1, apr_skiplist *sl2)

Detailed Description

Refer to http://en.wikipedia.org/wiki/Skip_list for information about the purpose of and ideas behind skip lists.

Typedef Documentation

apr_skiplist

typedef struct apr_skiplist apr_skiplist

Opaque structure used to represent the skip list

apr_skiplist_compare

typedef int(* apr_skiplist_compare) (void *, void *)

apr_skiplist_compare is the function type that must be implemented per object type that is used in a skip list for comparisons to maintain order

apr_skiplist_freefunc

typedef void(* apr_skiplist_freefunc) (void *)

apr_skiplist_freefunc is the function type that must be implemented to handle elements as they are removed from a skip list.

apr_skiplistnode

typedef struct apr_skiplistnode apr_skiplistnode

Opaque structure

Function Documentation

apr_skiplist_add()

apr_skiplistnode* apr_skiplist_add	(	apr_skiplist *	sl,
		void *	data
	)

Add an element into the skip list using the existing comparison function allowing for duplicates.

Parameters

sl	The skip list
data	The element to insert

Remarks

If no comparison function has been set for the skip list, the element will not be inserted and NULL will be returned.

apr_skiplist_add_compare()

apr_skiplistnode* apr_skiplist_add_compare	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplist_compare	comp
	)

Add an element into the skip list using the specified comparison function allowing for duplicates.

Parameters

sl	The skip list
data	The element to add
comp	The comparison function to use for placement into the skip list

apr_skiplist_add_index()

void apr_skiplist_add_index	(	apr_skiplist *	sl,
		apr_skiplist_compare	XXX1,
		apr_skiplist_compare	XXX2
	)

Set the indexing functions to the specified comparison functions and rebuild the index.

Parameters

sl	The skip list
XXX1	FIXME
XXX2	FIXME

Remarks

If an index already exists, it will not be replaced and the comparison functions will not be changed.

apr_skiplist_alloc()

void* apr_skiplist_alloc	(	apr_skiplist *	sl,
		size_t	size
	)

Allocate memory using the same mechanism as the skip list.

Parameters

sl	The skip list
size	The amount to allocate

Remarks

If a pool was provided to apr_skiplist_init(), memory will be allocated from the pool or from a free list maintained with the skip list. Otherwise, memory will be allocated using the C standard library heap functions.

apr_skiplist_destroy()

void apr_skiplist_destroy	(	apr_skiplist *	sl,
		apr_skiplist_freefunc	myfree
	)

Remove each element from the skip list.

Parameters

sl	The skip list
myfree	A function to be called for each removed element

apr_skiplist_element()

void* apr_skiplist_element

(

apr_skiplistnode *

iter

)

Return the element of the skip list node

Parameters

iter	The skip list node

apr_skiplist_find()

void* apr_skiplist_find	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplistnode **	iter
	)

Return the next matching element in the skip list using the current comparison function.

Parameters

sl	The skip list
data	The value to search for
iter	A pointer to the returned skip list node representing the element found

apr_skiplist_find_compare()

void* apr_skiplist_find_compare	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplistnode **	iter,
		apr_skiplist_compare	func
	)

Return the next matching element in the skip list using the specified comparison function.

Parameters

sl	The skip list
data	The value to search for
iter	A pointer to the returned skip list node representing the element found
func	The comparison function to use

apr_skiplist_free()

void apr_skiplist_free	(	apr_skiplist *	sl,
		void *	mem
	)

Free memory using the same mechanism as the skip list.

Parameters

sl	The skip list
mem	The object to free

Remarks

If a pool was provided to apr_skiplist_init(), memory will be added to a free list maintained with the skip list and be available to operations on the skip list or to other calls to apr_skiplist_alloc(). Otherwise, memory will be freed using the C standard library heap functions.

apr_skiplist_getlist()

apr_skiplistnode* apr_skiplist_getlist

(

apr_skiplist *

sl

)

Return the list maintained by the skip list abstraction.

Parameters

sl	The skip list

apr_skiplist_height()

int apr_skiplist_height

(

const apr_skiplist *

sl

)

Return the height of the list (number of skip paths), in O(1).

Parameters

sl	The skip list

apr_skiplist_init()

apr_status_t apr_skiplist_init	(	apr_skiplist **	sl,
		apr_pool_t *	p
	)

Allocate a new skip list

Parameters

sl	The pointer in which to return the newly created skip list
p	The pool from which to allocate the skip list (optional).

Remarks

Unlike most APR functions, a pool is optional. If no pool is provided, the C standard library heap functions will be used instead.

apr_skiplist_insert()

apr_skiplistnode* apr_skiplist_insert	(	apr_skiplist *	sl,
		void *	data
	)

Insert an element into the skip list using the existing comparison function if it does not already exist.

Parameters

sl	The skip list
data	The element to insert

Remarks

If no comparison function has been set for the skip list, the element will not be inserted and NULL will be returned.

apr_skiplist_insert_compare()

apr_skiplistnode* apr_skiplist_insert_compare	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplist_compare	comp
	)

Insert an element into the skip list using the specified comparison function if it does not already exist.

Parameters

sl	The skip list
data	The element to insert
comp	The comparison function to use for placement into the skip list

apr_skiplist_last()

void* apr_skiplist_last	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplistnode **	iter
	)

Return the last matching element in the skip list using the current comparison function.

Parameters

sl	The skip list
data	The value to search for
iter	A pointer to the returned skip list node representing the element found

apr_skiplist_last_compare()

void* apr_skiplist_last_compare	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplistnode **	iter,
		apr_skiplist_compare	comp
	)

Return the last matching element in the skip list using the specified comparison function.

Parameters

sl	The skip list
data	The value to search for
iter	A pointer to the returned skip list node representing the element found
comp	The comparison function to use

apr_skiplist_merge()

apr_skiplist* apr_skiplist_merge	(	apr_skiplist *	sl1,
		apr_skiplist *	sl2
	)

Merge two skip lists. XXX SEMANTICS

Parameters

sl1	One of two skip lists to be merged
sl2	The other of two skip lists to be merged

apr_skiplist_next()

void* apr_skiplist_next	(	apr_skiplist *	sl,
		apr_skiplistnode **	iter
	)

Return the next element in the skip list.

Parameters

sl	The skip list
iter	On entry, a pointer to the skip list node to start with; on return, a pointer to the skip list node representing the element returned

Remarks

If iter points to a NULL value on entry, NULL will be returned.

apr_skiplist_peek()

void* apr_skiplist_peek

(

apr_skiplist *

sl

)

Return the first element in the skip list, leaving the element in the skip list.

Parameters

sl	The skip list

Remarks

NULL will be returned if there are no elements

apr_skiplist_pop()

void* apr_skiplist_pop	(	apr_skiplist *	sl,
		apr_skiplist_freefunc	myfree
	)

Return the first element in the skip list, removing the element from the skip list.

Parameters

sl	The skip list
myfree	A function to be called for the removed element

Remarks

NULL will be returned if there are no elements

apr_skiplist_preheight()

int apr_skiplist_preheight

(

const apr_skiplist *

sl

)

Return the predefined maximum height of the skip list.

Parameters

sl	The skip list

apr_skiplist_previous()

void* apr_skiplist_previous	(	apr_skiplist *	sl,
		apr_skiplistnode **	iter
	)

Return the previous element in the skip list.

Parameters

sl	The skip list
iter	On entry, a pointer to the skip list node to start with; on return, a pointer to the skip list node representing the element returned

Remarks

If iter points to a NULL value on entry, NULL will be returned.

apr_skiplist_remove()

int apr_skiplist_remove	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplist_freefunc	myfree
	)

Remove an element from the skip list using the existing comparison function for locating the element. In the case of duplicates, the 1st entry will be removed.

Parameters

sl	The skip list
data	The element to remove
myfree	A function to be called for each removed element

Remarks

If the element is not found, 0 will be returned. Otherwise, the heightXXX will be returned.

If no comparison function has been set for the skip list, the element will not be removed and 0 will be returned.

apr_skiplist_remove_all()

void apr_skiplist_remove_all	(	apr_skiplist *	sl,
		apr_skiplist_freefunc	myfree
	)

Remove all elements from the skip list.

Parameters

sl	The skip list
myfree	A function to be called for each removed element

apr_skiplist_remove_compare()

int apr_skiplist_remove_compare	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplist_freefunc	myfree,
		apr_skiplist_compare	comp
	)

Remove an element from the skip list using the specified comparison function for locating the element. In the case of duplicates, the 1st entry will be removed.

Parameters

sl	The skip list
data	The element to remove
myfree	A function to be called for each removed element
comp	The comparison function to use for placement into the skip list

Remarks

If the element is not found, 0 will be returned. Otherwise, the heightXXX will be returned.

apr_skiplist_remove_node()

int apr_skiplist_remove_node	(	apr_skiplist *	sl,
		apr_skiplistnode *	iter,
		apr_skiplist_freefunc	myfree
	)

Remove a node from the skip list.

Parameters

sl	The skip list
iter	The skip list node to remove
myfree	A function to be called for the removed element

apr_skiplist_replace()

apr_skiplistnode* apr_skiplist_replace	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplist_freefunc	myfree
	)

Add an element into the skip list using the existing comparison function removing the existing duplicates.

Parameters

sl	The skip list
data	The element to insert
myfree	A function to be called for each removed duplicate

Remarks

If no comparison function has been set for the skip list, the element will not be inserted, none will be replaced, and NULL will be returned.

apr_skiplist_replace_compare()

apr_skiplistnode* apr_skiplist_replace_compare	(	apr_skiplist *	sl,
		void *	data,
		apr_skiplist_freefunc	myfree,
		apr_skiplist_compare	comp
	)

Add an element into the skip list using the specified comparison function removing the existing duplicates.

Parameters

sl	The skip list
data	The element to insert
comp	The comparison function to use for placement into the skip list
myfree	A function to be called for each removed duplicate

Remarks

If no comparison function has been set for the skip list, the element will not be inserted, none will be replaced, and NULL will be returned.

apr_skiplist_set_compare()

void apr_skiplist_set_compare	(	apr_skiplist *	sl,
		apr_skiplist_compare	XXX1,
		apr_skiplist_compare	XXX2
	)

Set the comparison functions to be used for searching the skip list.

Parameters

sl	The skip list
XXX1	FIXME
XXX2	FIXME

Remarks

If existing comparison functions are being replaced, the index will be replaced during this call. That is a potentially expensive operation.

apr_skiplist_set_preheight()

void apr_skiplist_set_preheight	(	apr_skiplist *	sl,
		int	to
	)

Set a predefined maximum height for the skip list.

Parameters

sl	The skip list
to	The preheight to set, or a nul/negative value to disable.

Remarks

When a preheight is used, the height of each inserted element is computed randomly up to this preheight instead of the current skip list's height plus one used by the default implementation. Using a preheight can probably ensure more fairness with long living elements (since with an adaptative height, former elements may have been created with a low height, hence a longest path to reach them while the skip list grows). On the other hand, the default behaviour (preheight <= 0) with a growing and decreasing maximum height is more adaptative/suitable for short living values.

Note

Should be called before any insertion/add.

apr_skiplist_size()

size_t apr_skiplist_size

(

const apr_skiplist *

sl

)

Return the size of the list (number of elements), in O(1).

Parameters

sl	The skip list