1. A computer-implemented method for simulating data flow using a dataflow computing system, the method comprising: a dataflow diagram that includes a plurality of operators, wherein each of the operators includes at least one input port or at least one output port; a plurality of arcs, wherein each of the arcs connects one of the output ports of one of the plurality operators to one of the input ports of a different one of the plurality of operators; a plurality of data items that flow in streams along the plurality of arcs between the plurality of operators; grouping the plurality of data items into a particle at a first operator included in the plurality of operators to form a particle grouping, wherein the first operator includes meta ports, wherein the meta ports include an arc-level meta port and a particle-level meta port, wherein the arc-level meta-port provides an arc-level meta-state that holds the state execution from a process initialization point to a process termination point, and wherein the particle-level meta-port provides a particle-level meta-state that provides an execution state of an input particle at any given point of time; performing, at the first operator, computations on the particle grouping, resulting in a computed plurality of data items; transmitting, from the first operator, the computed plurality of data items over one of the plurality of arcs to a second operator included in the plurality of operators; producing control data items at one of the meta ports included on the first operator based upon meta-state transitions that are in response to the computations performed by the first operator on the particle grouping; and transmitting the control data items from the first operator to one of the plurality of operators, wherein the control data items control the flow of the computed plurality of data items.