Lazy Threads: Implementing a Fast Parallel Call

In this paper, we describe lazy threads, a new approach for implementing multithreaded execution models on conventional machines. We show how they can implement a parallel call at nearly the efficiency of a sequential call. The central idea is to specialize the representation of a parallel call so that it can execute as a parallel-ready sequential call. This allows excess parallelism to degrade into sequential calls with the attendant efficient stack management and direct transfer of control and data, yet a call that truly needs to execute in parallel, gets its own thread of control. The efficiency of lazy threads is achieved through a careful attention to storage management and a code generation strategy that allows us to represent potential parallel work with no overhead.