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rb_tree: update augmentation after element change

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For an augmented rb_tree, allow a faster alternative to removing an
element from the tree, tweaking it slightly, and inserting it back
into the tree, knowing that its relative position in the tree is
unchanged. Instead, just change the element and invoke
RB_UPDATE_AUGMENT to fix the augmentation data for all the nodes in
the tree.

Reviewed by:	kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D36010
This commit is contained in:
Doug Moore 2022-08-02 11:19:46 -05:00
parent 3dce6f96e5
commit 35557a0d91
2 changed files with 30 additions and 12 deletions
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24
share/man/man3/tree.3
View File

@ -100,6 +100,7 @@
.Nm RB_REMOVE ,
.Nm RB_REINSERT ,
.Nm RB_AUGMENT
.Nm RB_UPDATE_AUGMENT
.Nd "implementations of splay and rank-balanced (wavl) trees"
.Sh SYNOPSIS
.In sys/tree.h
@ -196,6 +197,8 @@
.Fn RB_REINSERT NAME "RB_HEAD *head" "struct TYPE *elm"
.Ft "void"
.Fn RB_AUGMENT NAME "struct TYPE *elm"
.Ft "void"
.Fn RB_UPDATE_AUGMENT NAME "struct TYPE *elm"
.Sh DESCRIPTION
These macros define data structures for different types of trees:
splay trees and rank-balanced (wavl) trees.
@ -592,12 +595,25 @@ macro updates augmentation data of the element
in the tree.
By default, it has no effect.
It is not meant to be invoked by the RB user.
If RB_AUGMENT is defined by the RB user, then when an element is
inserted or removed from the tree, it is invoked for every element in
the tree that is the root of an altered subtree, working from the
bottom of the tree up to the top.
If
.Fn RB_AUGMENT
is defined by the RB user, then when an element is inserted or removed
from the tree, it is invoked for every element in the tree that is the
root of an altered subtree, working from the bottom of the tree up to
the top.
It is typically used to maintain some associative accumulation of tree
elements, such as sums, minima, maxima, and the like.
.Pp
The
.Fn RB_UPDATE_AUGMENT
macro updates augmentation data of the element
.Fa elm
and its ancestors in the tree.
If RB_AUGMENT is defined by the RB user, then when an element in the
tree is changed, without changing the order of items in the tree,
invoking this function on that element restores consistency of the
augmentation state of the tree as if the element had been removed and
inserted again.
.Sh EXAMPLES
The following example demonstrates how to declare a rank-balanced tree
holding integers.

18
sys/sys/tree.h
View File

@ -371,6 +371,13 @@ struct { \
#define RB_AUGMENT(x) break
#endif
#define RB_UPDATE_AUGMENT(elm, field) do { \
__typeof(elm) tmp = (elm); \
do { \
RB_AUGMENT(tmp); \
} while ((tmp = RB_PARENT(tmp, field)) != NULL); \
} while (0)
#define RB_SWAP_CHILD(head, out, in, field) do { \
if (RB_PARENT(out, field) == NULL) \
RB_ROOT(head) = (in); \
@ -678,11 +685,9 @@ name##_RB_REMOVE(struct name *head, struct type *elm) \
RB_SWAP_CHILD(head, old, elm, field); \
if (child != NULL) \
RB_SET_PARENT(child, parent, field); \
if (parent != NULL) \
if (parent != NULL) { \
name##_RB_REMOVE_COLOR(head, parent, child); \
while (parent != NULL) { \
RB_AUGMENT(parent); \
parent = RB_PARENT(parent, field); \
RB_UPDATE_AUGMENT(parent, field); \
} \
return (old); \
}
@ -714,10 +719,7 @@ name##_RB_INSERT(struct name *head, struct type *elm) \
else \
RB_RIGHT(parent, field) = elm; \
name##_RB_INSERT_COLOR(head, elm); \
while (elm != NULL) { \
RB_AUGMENT(elm); \
elm = RB_PARENT(elm, field); \
} \
RB_UPDATE_AUGMENT(elm, field); \
return (NULL); \
}