[pron]

The short answer is that you can't just use any blocking code. The Comsat project (https://github.com/puniverse/comsat) contains integrations of popular libraries with Quasar fibers, without change to their API. Under the hood, this is done using transformations made available in the FiberAsync class. Like eitany said, you can use FiberAsync to integrate the library yourself, or wait for an integration module in Comsat.

If library provides asynchronous APIs, it would yield great performance when integrated with Quasar fibers. If not (like JDBC), it would work as well as it does on regular threads, but won't interfere with all the other great stuff fibers can do.