Clojure core.async, channel vs port

Question

In Clojure core.async, are channels and ports the same thing? If not what's the difference? In watching the video Timothy Baldridge - Core.Async, he creates a channel

(def c (chan))

Then later

(<!! c)

c is channel yet the docs for <!! state (emphasis added)

Usage: (<!! port) takes a val from port. Will return nil if closed. Will block if nothing is available.

It's not clear looking at the core.async docs.

Aleš Roubíček · Accepted Answer · 2015-05-05 13:47:58Z

14

Yes, chans are ports.

port is in the name of the protocol that these implement

(defprotocol ReadPort
  (take! [port fn1-handler] "derefable val if taken, nil if take was enqueued"))

which is used by impl/take in:

(defn <!!
  "takes a val from port. Will return nil if closed. Will block if nothing is available."
  [port]
  (let [p (promise)
        ret (impl/take! port (fn-handler (fn [v] (deliver p v))))]
    (if ret
      @ret
      (deref p))))

and the name port is used very consistently throughout async.clj. Conceptually this is useful because not everything that core.async works on will be a channel. other things can implement ReadPort and WritePort and therefore play nicely with core.async.

edited May 5, 2015 at 13:47

Aleš Roubíček

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answered May 2, 2015 at 0:57

Arthur Ulfeldt

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2 Comments

Petrus Theron Over a year ago

Your answer, while well-written, does not explain why I need to know the difference between a chan and a port. The documentation shows <! being called in a go-block, but not <!!. Why?

Arthur Ulfeldt Over a year ago

you only need to know the difference if you are adding a new datatype that implements the port interfaces to allow it to send and receive data from other things in the core.async ecosystem. Chans are ports, and other things are as well.

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