High Performance Relaying of C++11 Objects across Processes and Logic-Labeled Finite-State Machines

Abstract

We present gusimplewhiteboard, a software architecture analogous to ROS:services and ROS:messages, that enables the construction and extremely efficient inter-process relaying of message-types as C++11 objects, All gusimplewhiteboard objects reside in shared memory. Moreover, our principle is to use idempotent message communication, in direct contrast to previously released platforms for roboticmodule communication, that are based on an event-driven subscriber model that queues and multi-threads. We combine this with compiled, time-triggered, logic-labeled finite state machines (llfsms) the are executed concurrently, but scheduled sequentially, in an extremely efficient manner, removing all race conditions and requirements for explicit synchronisation. Together, these tools enable effective robotic behaviour design, where arrangements of llfsms can be organised as hierarchies of machines and submachines, enabling composition of very complex systems. They have proven to be very powerful for Model-Driven Development, capable of simulation, validation, and formal verification.

Communication Within Multi-FSM Based Robotic Systems

“…The architecture of an embodied agent presented in Section 3 is implemented using several earlier-mentioned concepts. Here we shall concentrate on two important ones associated with the communication and behaviour selection [31]: the whiteboard, which is used as the main communication means between subsystems, and Logic-Labelled Finite State Machines (LLFSMs), which govern the actions of each of the subsystems present in the agent, including the exchange of information between subsystems. The whiteboard is our implementation of the general concept of a blackboard [42], thus whenever we refer here to the former we refer to our implementation and for the general concept, the latter is referred to.…”

“…The gusimplewhiteboard (Griffith University Simple Whiteboard) is a library for organising inter-process communication [31]. It implements a mutation of the general blackboard concept [42].…”

“…The implementation of the distributed version of the whiteboard uses efficient, fault-tolerant communication for distributed systems as presented in [11,51,57] [52,53]. Compared to the DCPS [58], the whiteboard does not offer inherent mechanisms for distributed reconfiguration, but offers a statically defined data classes and O(1), fail-silent communication within bounded real-time constraints [31]. A more detailed discussion of the networked version of the whiteboard [61] is presented in Section 6.…”

“…Whilst the proposed whiteboard can be used in both push and pull modes, the latter should be the method of choice. In the majority of middleware, the structure of the contents of the messages transferred is limited, whilst in gusimplewhiteboard any C++11 objects can be used [31].…”

“…As none of the ROS communication mechanisms satisfies the above-mentioned requirements, the whiteboard was chosen (in fact, a ROS package for the whiteboard is available at [67]). This approach provides intra-system inter-process communication, which does not block neither the producer nor the consumer; as it operates on common memory it is very low-latency [31,47]; by using the pull mode of operation it operates in time triggered mode; and moreover it can be used both by threads and processes in the same fashion.…”