3 ms·

I'm a clojure newb myself, but I thought STM transactions weren't allowed to have side-effects and IO would be a side-effect, no?

• jrheard 14y ago
  Refs and atoms shouldn't have side effects, but agents are great for performing side effects. From page 214 of Clojure Programming: Unlike refs and atoms, it is perfectly safe to use agents to coordinate I/O and perform other blocking operations. This makes them a vital piece of any complete application that use refs and Clojure’s STM to maintain program state over time. Further, thanks to their semantics, agents are often an ideal construct for simplifying asynchronous processing involving I/O even if refs are not involved at all. Further: Agents are integrated into Clojure’s STM implementation such that actions dispatched using send and send-off from within the scope of a transaction will be held in reserve until that transaction is successfully committed. This means that, even if a transaction retries 100 times, a sent action is only dispatched once, and that all of the actions sent during the course of a transaction’s runtime will be queued at once after the transaction commits.