1. A computer-implemented method for facilitating 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 merging the creation runtime context and the subsequent-execution runtime context into a single merged context and executing the single merge context by a single thread.