Abstract PicoThreads: Lightweight Threads in Java

often require complicated, split-phase, event-based implementations. Threads appear to be an attractive alternative because they allow the programmer to write a single sequence of operations and ignore the points at which the execution may be blocked. Unfortunately, the typical amount of memory required to support this technique prevents applications from scaling to large numbers of threads. Rather than relying on event-based programming, we use a program transformation to provide a lowcost thread implementation. This transformation retains the advantages of user-scheduled, eventbased programs, yet efficiently supports large numbers of threads. We replace the standard Java thread mechanism with lightweight PicoThreads and a cooperative, event-based, user-level scheduler. This is accompanied by a PicoThread-aware, asynchronous network library. To evaluate our implementation, we measure the performance of a simple web crawler running thousands of threads. Our results show that PicoThreaded programs perform comparably or substantially better than threaded programs when using large numbers of threads.