Lazy Threads: Compiler and Runtime Structures for Fine-Grained Parallel Programming

Many modern parallel languages support dynamic creation of threads or require multithreading in their implementations. The threads describe the logical parallelism in the program. For ease of expression and better resource utilization, the logical parallelism in a program often exceeds the physical parallelism of the machine and leads to applications with many fine-grained threads. In practice, however, most logical threads need not be independent threads. Instead, they could be run as sequential calls, which are inherently cheaper than independent threads. The challenge is that one cannot generally predict which logical threads can be implemented as sequential calls. In lazy multithreading systems each logical thread begins execution sequentially (with the attendant efficient stack management and direct transfer of control and data). Only if a thread truly must execute in parallel does it get its own thread of control.