Execution Shadow processing was motivated, in part, by a tool called AE that supports abstract execution [17]. AE is used for efficient generation of detailed program traces. A source program, in C, is instrumented to record a small set of key events during execution. After execution these events serve as input to an abstract version of the original program that can recreate a full trace of the original program. The events recorded by the original program include control flow decisions. These are essentially the same data needed by a shadow process to follow a main process. AE is a post-run technique that shifts some of the costs involved in tracing certain incidents during a program's execution to the program that uses those incidents. In contrast, shadow processing is a run-time technique that removes expensive tracing from the critical execution path of a program and shifts it to another processor. Table 7: Concurrent Guarding using Shadow Processing: (user + system) time Program ...