Signals, Timers, and Continuations for Multithreaded User-Level Protocols

Precise timing and asynchronous I/O are appealing features for many applications. Unix kernels provide such features on a per-process basis, using signals to communicate asynchronous events to applications. Per-process signals and timers are grossly inadequate for complex multithreaded applications that require perthread signals and timers that operate at finer granularities. To respond to this need, we present a scheme that integrates asynchronous (Unix) signals with userlevel threads, using the Ariadne system as a platform. This is done with a view towards support for portable, multithreaded, and multiprotocol distributed applications viz. the CLAM (connectionless, lightweight, and multiway) communications library. In the same context, we propose the use of continuations as an efficient mechanism for reducing (thread) context-switching and busy-wait overheads in multithreaded protocols. Our proposal for integrating timers and signal-handling mechanisms not only solves problems relate..