Messages in this thread | | | Date | Fri, 19 Jan 2007 14:41:55 -0800 | From | Randy Dunlap <> | Subject | Re: [PATCH] Documentation/rbtree.txt |
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On Thu, 18 Jan 2007 15:33:25 -0500 Rob Landley wrote:
> Signed-off-by: Rob Landley <rob@landley.net> > > Documentation for lib/rbtree.c. > > -- > > I'm not an expert on this but I was asked to write up some documentation > for rbtree in the Linux kernel, and as long as it's there... > > I'm sure if I screwed something up somebody will point it out to me, loudly. > :)
Hi,
Looks pretty good to me. I have a few minor nits (below).
> --- /dev/null 2006-05-30 21:33:22.000000000 -0400 > +++ linux-2.6.19.2/Documentation/rbtree.txt 2007-01-18 11:57:50.000000000 -0500 > @@ -0,0 +1,186 @@ > +Red-black Trees (rbtree) in Linux > +January 18, 2007 > +Rob Landley <rob@landley.net> > +============================= > + > +What are red-black trees, and what are they for? > +------------------------------------------------ > + > +Red-black trees are a type of self-balancing binary search tree, used for > +storing sortable key/value data pairs. This differs from radix trees (which > +are used to efficiently store sparse arrays and thus use long integer indexes > +to insert/access/delete nodes) and hash tables (which are not kept sorted to > +be easily traversed in order, and must be tuned for a specific size and > +hash function where rbtrees scale gracefully storing arbitrary keys). > + > +Red-black trees are similar to AVL trees, but provide faster realtime bounded
real-time
> +worst case performance for insertion and deletion (at most two rotations and > +three rotations, respectively, to balance the tree), with slightly slower > +(but still O(log n)) lookup time. > + > +To quote Linux Weekly News: > + ... > + > +This document covers use of the Linux rbtree implementation. For more > +information on the nature and implementation of Red Black Trees, see: > + ... > + > +Linux implementation of red-black trees > +--------------------------------------- > + > +Linux's rbtree implementation lives in the file "lib/rbtree.c". To use it, > +"#include <linux/rbtree.h>". > + > +The Linux rbtree implementation is optimized for speed, and thus has one > +less layer of indirection (and better cache locality) than more traditional > +tree implementations. Instead of using pointers to separate rb_node and data > +structures, each instance of struct rb_node is embedded in the data structure > +it organizes. And instead of using a comparison callback function pointer, > +users are expected to write their own tree search and insert functions > +which call the provided rbtree functions. Locking is also left up to the > +user of the rbtree code. > + > +Creating a new rbtree > +--------------------- > + > +Data nodes in an rbtree tree are structures containing a struct rb_node member: > + > + struct mytype { > + struct rb_node node; > + char *keystring; > + }; > + > +When dealing with a pointer to the embedded struct rb_node, the containing data > +structure may be accessed with the standard container_of() macro. In addition, > +individual members may be accessed directly via rb_entry(node, type, member). > + > +At the root of each rbtree is a rb_root structure, which is initialized to be > +empty via:
an rb_root
> + > + struct rb_root mytree = RB_ROOT; > + > +Searching for a value in an rbtree > +---------------------------------- > + > +Writing a search function for your tree is fairly straightforward: start at the > +root, compare each value, and follow the left or right branch as necessary. > + > +Example: > + > + struct mytype *my_search(struct rb_root *root, char *string) > + { > + struct rb_node *node = root->rb_node; > + > + while (node) { > + struct mytype *data = container_of(node, struct mytype, node); > + int result; > + > + result = strcmp(string, data->keystring); > + > + if (result < 0) node = node->rb_left; > + else if (result > 0) node = node->rb_right; > + else return data; > + } > + return NULL; > + } > + > +Inserting data into an rbtree > +----------------------------- > + > +Inserting data in the tree involves first searching for the place to insert the > +new node, then inserting the node and rebalancing ("recoloring") the tree. > + > +The search for insertion differs from the previous search by finding the > +location of the pointer on which to graft the new node. The new node also > +needs a link to its' parent node for rebalancing purposes.
its
> + > +Example: > + > + int my_insert(struct rb_root *root, struct mytype *data) > + { > + struct rb_node **new = &(root->rb_node), *parent = NULL; > + > + // Figure out where to put new node > + while (*new) { > + struct mytype *this = container_of(*new, struct mytype, node); > + int result = strcmp(data->keystring, this->keystring); > + > + parent = *new; > + if (result < 0) new = &((*new)->rb_left); > + else if (result > 0) new = &((*new)->rb_right); > + else return FALSE; > + } > + > + // Add new node and rebalance tree. > + rb_link_node(data->node, parent, new); > + rb_insert_color(data->node, root); > + > + return TRUE; > + }
Please use kernel CodingStyle in the kernel Documentation/ directory. That would mean /*...*/ comments instead of // and expanding the if/else lines to have their statements on separate lines....
> +Removing or replacing existing data in an rbtree > +------------------------------------------------ > + ... > + > +Iterating through the elements stored in an rbtree (in sort order) > +------------------------------------------------------------------ > + > +Four functions are provided for iterating through an rbtree's contents in > +sorted order. These work on arbitrary trees, and should not need to be > +modified or wrapped (except for locking purposes): > + > + struct rb_node *rb_first(struct rb_root *tree); > + struct rb_node *rb_last(struct rb_root *tree); > + struct rb_node *rb_next(struct rb_node *node); > + struct rb_node *rb_prev(struct rb_node *node); > + > +To start iterating, call rb_first() or rb_last() with a pointer to the root > +fo the tree, which will return a pointer to the node structure contained in
of
> +the first or last element in the tree. To continue, fetch the next or previous > +node by calling rb_next() or rb_prev() on the current node. This will return > +NULL when there are no more nodes left. > + > +The iterator functions return a pointer to the embedded struct rb_node, from > +which the containing data structure may be accessed with the container_of() > +macro, and individual members may be accessed directly via > +rb_entry(node, type, member).
Thanks.
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