Application programs supporting multiple contexts on a computer system having an operating system supporting threads. The method comprises processing a context processing instruction from the run-time application program, evaluating said instruction in relation to program-flow control yielding context-defining processing parameters, analyzing the context-defining processing parameters from the execution context of the context processing instruction in regard of program flow management by threads, mapping the context-processing instruction to a selected thread managing instruction, or to a selected set of thread managing instructions, having a respective program flow control effect equivalent to that of context-processing instruction, invoking the selected thread managing instruction or the set thereof, together with selected parameters so that that during runtime of the application program only one thread is allowed to execute at a time, and the program state of a thread is stored at a given point in time and is restored later from the point in time.