1. A computer-implemented method in a graphical modeling environment, the method comprising: providing a control initiator, where the control initiator provides a control signal to a control signal splitter, where: the control initiator is a block that uses a control signal to explicitly control execution of one or more subgraphs, and the control signal splitter accepts the control signal from the control initiator and splits the control signal into a first split control signal and a second split control signal; providing a first subgraph in the modeling environment, where: the first subgraph includes one or more blocks, and the first subgraph is connected to the control signal splitter; providing a second subgraph in the modeling environment, where: the second subgraph includes one or more blocks, and the second subgraph is connected to the control signal splitter; executing the first subgraph in a first thread to produce a first result when the first subgraph receives the first split control signal from the control signal splitter; and executing the second subgraph in a second thread to produce a second result when the second subgraph receives the second split control signal from the control signal splitter and where: the first split control signal and the second split control signal are output from the control signal splitter in an order that honors data dependencies from the first subgraph and second subgraph.