A computer program implemented method controls interruption of execution of tasks running in a multi-processing computer system to permit user intervention. The system includes a repository of data identifying preselected tasks for interruption and identifying the user defined circumstances for such interruption. It also has a plurality of task caches for storing subsets of the repository data for respective tasks. According to the method, the repository is scanned during an initiation phase of any task for data relevant to the task. Any such relevant data is stored in the respective task cache. The task is then executed and if a defined circumstance for the task arises by reference to the task cache, the task is interrupted to enable user intervention. This can include updating the repository to redefine the circumstances for interruption. Execution is then resumed and the respective task cache refreshed with any relevant repository updates.