patterns_page_2.clj

;; managing state

;; agents
;; --------------

(def score (agent 0))
(deref score) ;; 0
@score ;; 0
;; an agent is in charge of managing state.
;; agents guarantee that changes happen in the order they arrive.

(send score inc) ;; #<Agent@6d8f3cc5: 0>
;; send is async.
;; you have to send a function to the agent, which will be applied by
;; the agent, with its current state as a argument.
@score ;; 1

(send score + 100)
;; the first argument to the update function is always the state
;; an agent manages, but additional arguments to the function can be
;; supplied.

(send-off some-agent some-io-bound-fn)
;; Clojure uses a thead pool of cpu-count + 1 for send calls.
;; Instead, when using send-off, Clojure uses a separate thread, since
;; having a lot of i/o-bound threads in one pool can block the pool unnecessarily.
;; so use send-off for i/o-bound functions.