Older blog entries for oubiwann (starting at number 285)

29 Oct 2012 (updated 14 Mar 2013 at 04:03 UTC) »

Async in Clojure: Playing with Agents, Part I

Clojure has a very interesting async primitive: the agent. There is some good documentation on agents, but for those that come from a background such as mine (Python at Twisted), I thought it might be nice to present one way of using agents to mimic the familiar async + callback reactive-style programming.

Do note, however, that Clojure agents run in one of two threadpools (one intended for CPU-intensive tasks, and the other for I/O-intensive tasks). As such, this is quite different than the event-loop approach that Twisted uses (or async frameworks that utilize libraries such as libevent or libev). Twisted has the deferToThread functionality, which is ... well, not exactly close, really. Regardless, let's get started.

In the following examples, we're going to pretend we have huge files we'll be reading off a local disk.

What to Call
Clojure's agent function is very, very simple: you pass it a value (it's initial state) and some options, if needed. That's it.

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