Speculative processing mechanisms in a parallel Lisp machine: BIDDLE

In a system supporting parallel execution, speculative processing can be used to increase the amount of parallelism. The authors propose a speculative execution scheme for the data-driven Lisp machine BIDDLE. Execution priorities are assigned to instructions according to their nested position in conditional statements. These priorities are updated dynamically during execution as results of Boolean guards of conditional execution are returned. The authors describe the ways to maintain the environment and handle side effects and tuplespace in the speculative context. Each speculative branch is given a separate environment. Any side-effects made are merged into the environment of the calling instruction when the speculation is confirmed, and removed if they are unwanted. It is also demonstrated that infinite data structures can be supported by this scheme.