Multiprocessor support for event-driven programs

This paper presents a new asynchronous program-ming library (libasync-smp) that allows event-driven ap-plications to take advantage of multiprocessors by run-ning code for event handlers in parallel. To control the concurrency between events, the programmer can spec-ify a color for each event: events with the same color (the default case) are handled serially; events with dif-ferent colors can be handled in parallel. The program-mer can incrementally expose parallelism in existing event-driven applications by assigning different colors to computationally-intensive events that do not share muta-ble state. An evaluation of libasync-smp demonstrates that ap-plications achieve multiprocessor speedup with little pro-gramming effort. As an example, parallelizing the cryp-tography in the SFS file server required about 90 lines of changed code in two modules, out of a total of about 12,000 lines. Multiple clients were able to read large cached files from the libasync-smp SFS server running on a 4-CPU machine 2.5 times as fast as from an unmod-ified uniprocessor SFS server on one CPU. Applications without computationally intensive tasks also benefit: an event-driven Web server achieves 1.5 speedup on four CPUs with multiple clients reading small cached files.