In a processor system for executing a plurality of tasks, which respectively control execution of one or more of a plurality of processes, a method of restarting execution of a first process which is under control of a specific task being executed, after the first process is stopped to wait for occurrence of an event associated with at least one second process different from the first process, includes the steps of (a) detecting whether or not the event associated with the second process has occurred; (b) restarting the execution of the first process when it is detected that the event has occurred; (c) determining whether or not there is an execution waiting process when the event has not yet occurred; (d) executing an executing waiting process when there is any; and (e) repeating the steps (a) to (d) after execution of an execution waiting process when there is any or after the step (c) when there is not such an execution waiting process.