SIGNAL GTi: implementing task preemption and time intervals in the synchronous data flow language SIGNAL

This paper presents SIGNAL GTi, the encoding and implementation of an extension to the reactive data flow language SIGNAL with constructs for hierarchical task preemption. Tasks are defined as the association of a data-flow process with a time interval on which it is executed. The motivation for introducing these preemption structures is the need for the specification of different modes of interactions with the environment, and transitions between them (i.e. sequencing) an a nested way, especially in complex applications like robotics and discrete event control systems. A pre-processor to the SIGNAL compiler implements the encoding of the new constructs in the dataflow framework. This way, both data-flow and tasking paradigms are available within the same language-level framework, and the tools of the SIGNAL environment for optimization, simulation or proof are available.