1. A computer-implemented method in a graphical modeling environment, the method comprising: providing a first control initiator, where the first control initiator is connected to a first sub graph by a first control signal, where: the first control initiator is a block that uses the first control signal to explicitly control execution of the first subgraph; executing the first subgraph in a first thread whose execution is explicitly controlled; providing a second control initiator, where the second control initiator is connected to a second subgraph by a second control signal; executing the second subgraph in a second thread whose execution is explicitly controlled; interacting with a data synchronization block, where: the interacting allows a result from the first subgraph to be used by the second subgraph when the second sub graph is executing; with the data synchronization block, waiting for the first thread to finish executing before allowing the result to be used by the second subgraph when the second subgraph is executing; and producing an error when the result is used in the second thread without passing through the data synchronization block.