Improving the Parallel Execution of Behavior Trees

TL;DR

This paper introduces Concurrent Behavior Trees (CBTs), a generalized framework that enables safe parallel execution of actions in autonomous agents, addressing concurrency issues and enhancing modular control design.

Contribution

The paper proposes Concurrent BTs with progress and resource concepts, providing a mathematical foundation and practical robotics use cases for safe parallel action execution.

Findings

CBTs allow safe concurrent execution of actions.

Mathematical analysis supports the approach.

Use cases demonstrate practical benefits in robotics.

Abstract

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.