81,285 research outputs found
Improving the Parallel Execution of Behavior Trees
Behavior Trees (BTs) have become a popular framework for designing
controllers of autonomous agents in the computer game and in the robotics
industry. One of the key advantages of BTs lies in their modularity, where
independent modules can be composed to create more complex ones. In the
classical formulation of BTs, modules can be composed using one of the three
operators: Sequence, Fallback, and Parallel. The Parallel operator is rarely
used despite its strong potential against other control architectures as Finite
State Machines. This is due to the fact that concurrent actions may lead to
unexpected problems similar to the ones experienced in concurrent programming.
In this paper, we introduce Concurrent BTs (CBTs) as a generalization of BTs in
which we introduce the notions of progress and resource usage. We show how CBTs
allow safe concurrent executions of actions and we analyze the approach from a
mathematical standpoint. To illustrate the use of CBTs, we provide a set of use
cases in robotics scenarios
Concurrent rebalancing on hyperred-black trees
The HyperRed-Black trees are a relaxed version of Red-Black
trees accepting high degree of concurrency. In the Red-Black trees
consecutive red nodes are forbidden. This restriction has been
withdrawn in the Chromatic trees. They have been introduced by
O.~Nurmi and E.~Soisalon-Soininen to work in a concurrent
environment. A Chromatic tree can have big clusters of red nodes
surrounded by black nodes. Nevertheless, concurrent rebalancing of
Chromatic trees into Red-Black trees has a serious drawback:
in big cluster of red nodes only the top node can be updated. Direct
updating inside the cluster is forbidden. This approach gives us
limited degree of concurrency. The HyperRed-Black trees has been
designed to solve this problem. It is possible to update red nodes in
the inside of a red cluster. In a HyperRed-Black tree nodes can
have a multiplicity of colors; they can be red, black or hyper-red.Postprint (published version
A Unified approach to concurrent and parallel algorithms on balanced data structures
Concurrent and parallel algorithms are different. However, in the case of dictionaries, both kinds of algorithms share many
common points. We present a unified approach emphasizing these points. It is based on a careful analysis of the sequential
algorithm, extracting from it the more basic facts, encapsulated later on as local rules. We apply the method to the
insertion algorithms in AVL trees. All the concurrent and parallel insertion algorithms have two main phases. A
percolation phase, moving the keys to be inserted down, and a rebalancing phase. Finally, some other algorithms and
balanced structures are discussed.Postprint (published version
Efficient Lock-free Binary Search Trees
In this paper we present a novel algorithm for concurrent lock-free internal
binary search trees (BST) and implement a Set abstract data type (ADT) based on
that. We show that in the presented lock-free BST algorithm the amortized step
complexity of each set operation - {\sc Add}, {\sc Remove} and {\sc Contains} -
is , where, is the height of BST with number of nodes
and is the contention during the execution. Our algorithm adapts to
contention measures according to read-write load. If the situation is
read-heavy, the operations avoid helping pending concurrent {\sc Remove}
operations during traversal, and, adapt to interval contention. However, for
write-heavy situations we let an operation help pending {\sc Remove}, even
though it is not obstructed, and so adapt to tighter point contention. It uses
single-word compare-and-swap (\texttt{CAS}) operations. We show that our
algorithm has improved disjoint-access-parallelism compared to similar existing
algorithms. We prove that the presented algorithm is linearizable. To the best
of our knowledge this is the first algorithm for any concurrent tree data
structure in which the modify operations are performed with an additive term of
contention measure.Comment: 15 pages, 3 figures, submitted to POD
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