1. A method for initiating processing of blocks of data within at least one flow of data input to a graph having a plurality of process stages, including at least one subscriber process stage, at least one publisher process stage, and optionally at least one intermediate process stage, the method including: generating a compute point indicator in response to a trigger event; propagating the compute point indicator through the graph, from each subscriber process stage through any intermediate process stages to each publisher process stage, as part of the flow of data; for each process stage, processing a current block of data associated with the process stage in response to receipt by the process stage of at least one compute point indicator from an immediately previous process stage associated with the process stage.