Profile-directed optimization of event-based programs

Events are used as a fundamental abstraction in programs ranging from graphical user interfaces (GUIs) to systems for building customized network protocols. While providing a flexible structuring and execution paradigm, events have the potentially serious drawback of extra execution overhead due to the indirection between modules that raise events and those that handle them. This paper describes an approach to addressing this issue using static optimization techniques. This approach, which exploits the underlying predictability often exhibited by event-based programs, is based on first profiling the program to identify commonly occurring event sequences. A variety of techniques that use the resulting profile information are then applied to the program to reduce the overheads associated with such mechanisms as indirect function calls and argument marshaling. In addition to describing the overall approach, experimental results are given that demonstrate the effectiveness of the techniques. These results are from event-based programs written for X Windows, a system for building GUIs, and Cactus, a system for constructing highly configurable distributed services and network protocols.