The present invention provides an array of parallel programmable processing engines interconnected by a switching network. At least some of the processing engines execute a thread, and at least some threads communicate with each other through communication objects either internally within one processing engine or through the network. A scheduling step of the parallel programmable processing engines is initiated by one or more events, an event being defined by a change of a state variable of a communication object. The array comprises: means for scheduling a scheduling step of the processing engines, the scheduling means comprising means for executing at least a first set of threads in parallel, means for updating state values of communications objects in response to the parallel executing step, and means for repeatedly and sequentially scheduling the executing means and the updating means until no more events occur. The present invention also provides a deterministic method of operating such an array.