A Procedural Interface for Program Directing 1 Rok

1 Summary Debugging and performance measurement tools are becoming more important in the development and maintenance of increasingly complex software. These tools belong to a class of programs, called directors, which are programs that monitor and control other programs. Through monitoring, directors analyze program execution at run time. Monitoring provides tracing primitives as well as access to program's variables, dynamic data structures, and its internal state. Results of the monitoring analysis can be used by the director itself to change the future program behavior or presented to a human user for an interactive review and possible feedback actions. The future program behavior is changed through controlling primitives which provide an organized way to modify data values as well as the program code. This paper presents a library of directing commands that enable the construction of powerful directors. The interface has been implemented as a run time subsystem running in the directed program's address space. The paper provides the description of the interface and the basic programming techniques in building directors. Examples of novel applications, built on the top of the directing interface, are illustrated by the directors for the visualization of program control and structured snapshots.