We have developed a new, portable I/O event manager for the Glasgow Haskell
Compiler (GHC) that scales to the needs of modern server applications. Our new code
is transparently available to existing Haskell applications. Performance at lower
concurrency levels is comparable with the existing implementation. We support
millions of concurrent network connections, with millions of active timeouts, from
a single multithreaded program, levels far beyond those achievable with the current
I/O manager. In addition, we provide a public API to developers who need to create
event-driven network applications.