In one embodiment, a method includes receiving a request to execute first program code that is configured to perform a step of a computation, wherein the request includes a current state of the computation, determining whether the first program code is to be invoked based on an execution condition, when the execution condition is true, executing the first program code based on the current state of the computation, and returning a response that includes a result of executing the first program code, and when the execution condition is false, returning a response indicating that the result of the executing is invalid. The execution condition may be false when an amount of time that has passed since a previous execution of the first program code is greater than a threshold time limit.