Skip list implementation

Overview

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

// 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;

// global 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_next(
    apr_skiplist* sl,
    apr_skiplistnode** iter
);

void*
apr_skiplist_previous(
    apr_skiplist* sl,
    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
);

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);

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

Detailed Documentation

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

Typedefs

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. A value <0 indicates placement after this node; a value of 0 indicates collision with this exact node; a value >0 indicates placement before this node.

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.

typedef struct apr_skiplist apr_skiplist

Opaque structure used to represent the skip list

typedef struct apr_skiplistnode apr_skiplistnode

Opaque structure

Global Functions

void*
apr_skiplist_alloc(
    apr_skiplist* sl,
    size_t size
)

Allocate memory using the same mechanism as the skip list. 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.

Parameters:

sl	The skip list
size	The amount to allocate

void
apr_skiplist_free(
    apr_skiplist* sl,
    void* mem
)

Free memory using the same mechanism as the skip list. 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.

Parameters:

sl	The skip list
mem	The object to free

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

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

Parameters:

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

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

Parameters:

sl	The skip list
XXX1	FIXME
XXX2	FIXME

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

Parameters:

sl	The skip list
XXX1	FIXME
XXX2	FIXME

apr_skiplistnode*
apr_skiplist_getlist(apr_skiplist* sl)

Return the list maintained by the skip list abstraction.

Parameters:

sl	The skip list

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

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

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

Return the next element in the skip list. If iter points to a NULL value on entry, NULL will be returned.

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

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

Return the previous element in the skip list. If iter points to a NULL value on entry, NULL will be returned.

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

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_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 (as determined by the comparison function) If no comparison function has been set for the skip list, the element will not be inserted and NULL will be returned.

Parameters:

sl	The skip list
data	The element to insert

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

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

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. 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.

Parameters:

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

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

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

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. NULL will be returned if there are no elements

Parameters:

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

void*
apr_skiplist_peek(apr_skiplist* sl)

Return the first element in the skip list, leaving the element in the skip list. NULL will be returned if there are no elements

Parameters:

sl	The skip list

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