1. A computer-implemented method for facilitating the development and execution of a software program, comprising: during execution of the software program: receiving a first context identifier that identifies a creation runtime context and a creation thread that are used to create a closure that captures a variable; receiving a second context identifier that identifies a subsequent-execution runtime context and a subsequent-execution thread for a subsequent execution of the closure; and preventing unsafe sharing of variables captured by closures by ensuring that the subsequent-execution runtime context corresponds to the creation runtime context by: in response to determining that the first context identifier does not correspond to the second context identifier, preventing the unsafe sharing of variables captured by closures by modifying the closure to execute within the creation thread.