The full API is browsable here.

Async is a library for asynchronous programming, i.e., programming where some part of the program must wait for things that happen at times determined by some external entity (like a human or another program). This includes pretty much any program that uses blocking calls (e.g., networking code, disk access), timeouts, or event loops (e.g., GUIs).

In a nutshell, the idea is to use non-preemptive user-level threads and first-class blocking operations with blocking expressed in the type system.

Read more in Chapter 18 of Real World OCaml.


Async comprises three packages, Async_kernel, Async_unix, and Async_extra.

You can most easily understand Async's API by reading the documentation of these individually.