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NAME

pmemobj_list_insert(), pmemobj_list_insert_new(), pmemobj_list_move(), pmemobj_list_remove() - non-transactional persistent atomic lists functions

SYNOPSIS

    #include <libpmemobj.h>
    int pmemobj_list_insert(PMEMobjpool *pop, size_t pe_offset, void *head,
        PMEMoid dest, int before, PMEMoid oid);
    PMEMoid pmemobj_list_insert_new(PMEMobjpool *pop, size_t pe_offset,
        void *head, PMEMoid dest, int before, size_t size,
        uint64_t type_num, pmemobj_constr constructor, void arg);
    int pmemobj_list_move(PMEMobjpool *pop,
        size_t pe_old_offset, void *head_old,
        size_t pe_new_offset, void *head_new,
        PMEMoid dest, int before, PMEMoid oid);
    int pmemobj_list_remove(PMEMobjpool *pop, size_t pe_offset,
        void *head, PMEMoid oid, int free);

DESCRIPTION

In addition to the container operations on internal object collections described in pmemobj_first(3), libpmemobj(7) provides a mechanism for organizing persistent objects in user-defined, persistent, atomic, circular, doubly-linked lists. All the routines and macros operating on the persistent lists provide atomicity with respect to any power-fail interruptions. If any of those operations is torn by program failure or system crash, on recovery they are guaranteed to be entirely completed or discarded, leaving the lists, persistent memory heap and internal object containers in a consistent state.

The persistent atomic circular doubly linked lists support the following functionality:

•   Insertion of an object at the head of the list, or at the end of the list.

•   Insertion of an object before or after any element in the list.

•   Atomic allocation and insertion of a new object at the head of the list, or at the end of the list.

•   Atomic allocation and insertion of a new object before or after any element in the list.

•   Atomic moving of an element from one list to the specific location on another list.

•   Removal of any object in the list.

•   Atomic removal and freeing of any object in the list.

•   Forward or backward traversal through the list.

A list is headed by a list_head structure containing the object handle of the first element on the list. The elements are doubly linked so that an arbitrary element can be removed without the need to traverse the list. New elements can be added to the list before or after an existing element, at the head of the list, or at the tail of the list. A list may be traversed in either direction.

The user-defined structure of each element must contain a field of type list_entry that holds the object handles to the previous and next element on the list. Both the list_head and the list_entry structures are declared in <libpmemobj.h>.

The functions below are intended to be used outside transactions - transactional variants are described in manpages to functions mentioned at TRANSACTIONAL OBJECT MANIPULATION in libpmemobj(7). Note that operations performed using this non-transactional API are independent from their transactional counterparts. If any non-transactional allocations or list manipulations are performed within an open transaction, the changes will not be rolled back if such a transaction is aborted or interrupted.

The list insertion and move functions use a common set of arguments to define where an object will be inserted into the list. dest identifies the element before or after which the object will be inserted, or, if dest is OID_NULL, indicates that the object should be inserted at the head or tail of the list. before determines where the object will be inserted:

•   POBJ_LIST_DEST_BEFORE - insert the element before the existing element dest

•   POBJ_LIST_DEST_AFTER - insert the element after the existing element dest

•   POBJ_LIST_DEST_HEAD - when dest is OID_NULL, insert the element at the head of the list

•   POBJ_LIST_DEST_TAIL - when dest is OID_NULL, insert the element at the tail of the list

    NOTE: Earlier versions of libpmemobj(7) do not define POBJ_LIST_DEST_BEFORE and POBJ_LIST_DEST_AFTER. Use 1 for before, and 0 for after.

The pmemobj_list_insert() function inserts the element represented by object handle oid into the list referenced by head, at the location specified by dest and before as described above. pe_offset specifies the offset of the structure that connects the elements in the list. All the handles head, dest and oid must point to objects allocated from memory pool pop. head and oid cannot be OID_NULL.

The pmemobj_list_insert_new() function atomically allocates a new object of given size and type type_num and inserts it into the list referenced by head at the location specified by dest and before as described above. pe_offset specifies the offset of the structure that connects the elements in the list. The handles head and dest must point to objects allocated from memory pool pop. Before returning, pmemobj_list_insert_new() calls the constructor function, passing the pool handle pop, the pointer to the newly allocated object ptr, and the arg argument. It is guaranteed that the allocated object is either properly initialized or, if the allocation is interrupted before the constructor completes, the memory space reserved for the object is reclaimed. head cannot be OID_NULL. The allocated object is also added to the internal container associated with type_num, as described in POBJ_FOREACH(3).

The pmemobj_list_move() function moves the object represented by object handle oid from the list referenced by head_old to the list referenced by head_new, inserting it at the location specified by dest and before as described above. pe_old_offset and pe_new_offset specify the offsets of the structures that connect the elements in the old and new lists, respectively. All the handles head_old, head_new, dest and oid must point to objects allocated from memory pool pop. head_old, head_new and oid cannot be OID_NULL.

The pmemobj_list_remove() function removes the object represented by object handle oid from the list referenced by head. If free is set, it also removes the object from the internal object container and frees the associated memory space. pe_offset specifies the offset of the structure that connects the elements in the list. Both head and oid must point to objects allocated from memory pool pop and cannot be OID_NULL.

RETURN VALUE

On success, pmemobj_list_insert(), pmemobj_list_remove() and pmemobj_list_move() return 0. On error, they return -1 and set errno appropriately.

On success, pmemobj_list_insert_new() returns a handle to the newly allocated object. If the constructor returns a non-zero value, the allocation is canceled, -1 is returned, and errno is set to ECANCELED. On other errors, OID_NULL is returned and errno is set appropriately.

SEE ALSO

pmemobj_first(3), POBJ_FOREACH(3), libpmemobj(7) and <https://pmem.io>