Doubly linked list. More...

#include <list.h>

Collaboration diagram for list_elem:

Data Fields
struct list_elem *	prev
	Previous list element. More...

struct list_elem *	next
	Next list element. More...

Detailed Description

Doubly linked list.

This implementation of a doubly linked list does not require use of dynamically allocated memory. Instead, each structure that is a potential list element must embed a struct list_elem member. All of the list functions operate on these `struct list_elem's. The list_entry macro allows conversion from a struct list_elem back to a structure object that contains it.

For example, suppose there is a needed for a list of ‘struct foo’. ‘struct foo’ should contain a ‘struct list_elem’ member, like so:

struct foo { struct list_elem elem; int bar; ...other members... };

Then a list of ‘struct foo’ can be be declared and initialized like so:

struct list foo_list;

list_init (&foo_list);

Iteration is a typical situation where it is necessary to convert from a struct list_elem back to its enclosing structure. Here's an example using foo_list:

struct list_elem *e;

for (e = list_begin (&foo_list); e != list_end (&foo_list); e = list_next (e)) { struct foo *f = list_entry (e, struct foo, elem); ...do something with f... }

You can find real examples of list usage throughout the source; for example, malloc.c, palloc.c, and thread.c in the threads directory all use lists.

The interface for this list is inspired by the list<> template in the C++ STL. If you're familiar with list<>, you should find this easy to use. However, it should be emphasized that these lists do no type checking and can't do much other correctness checking. If you screw up, it will bite you.

Glossary of list terms:

"front": The first element in a list. Undefined in an empty list. Returned by list_front().
"back": The last element in a list. Undefined in an empty list. Returned by list_back().
"tail": The element figuratively just after the last element of a list. Well defined even in an empty list. Returned by list_end(). Used as the end sentinel for an iteration from front to back.
"beginning": In a non-empty list, the front. In an empty list, the tail. Returned by list_begin(). Used as the starting point for an iteration from front to back.
"head": The element figuratively just before the first element of a list. Well defined even in an empty list. Returned by list_rend(). Used as the end sentinel for an iteration from back to front.
"reverse beginning": In a non-empty list, the back. In an empty list, the head. Returned by list_rbegin(). Used as the starting point for an iteration from back to front.
"interior element": An element that is not the head or tail, that is, a real list element. An empty list does not have any interior elements. List element.