Deferrable is one of EventMachine's mechanisms for lightweight concurrency. (Spawned Processes is another.)

Deferrable makes it easy and graceful to initiate a long-running ("deferrable") operation (such as a call to an external web site), and attach any number of code blocks to be executed when the deferrable operation completes.

This page is under construction. The intention is that this page will become the primary resource for learning about Deferrable. For now, see the file DEFERRABLES at the top level of the EM source distro for much more information on Deferrables.