Multithreading – how do I implement atoms in clojurescript?

In clojure to address concurrency, we can use an atom to write:

user=> (def my-atom (atom 0))
#'user/my-atom

user=> @my-atom
0

user=> (swap! my-atom inc)
1

user=> @my-atom
1

user=> (swap! my-atom (fn [n] (* (+ n n) 2)))
4

We know that this (in the clojure Implementation) is a wrapper around the Java atomic object

Interestingly, atoms are replicated in clojurescript is at the syntactic level - even if JavaScript runs without atomic references

My question is, how do I implement atoms in clojurescript? Are they just an object wrapper?

Solution

It only returns and assigns values

At the source https://github.com/clojure/clojurescript/blob/master/src/main/cljs/cljs/core.cljs#L4081

(deftype Atom [state Meta validator watches]
  ...
  IDeref
  (-deref [_] state) 
  ...)

And https://github.com/clojure/clojurescript/blob/master/src/main/cljs/cljs/core.cljs#L4110

(defn atom
  "Creates and returns an Atom ..."
  ([x] (Atom. x nil nil nil))
  ([x & {:keys [Meta validator]}] (Atom. x Meta validator nil)))

Check the implementation of swap! And reset! You will find:

(set! (. - status a) new value)

Then, go to https://github.com/clojure/clojurescript/blob/3bb97961cbc958aeaeac506222dc7b9dcb0e9fc1/src/clj/cljs/compiler.clj#L771 Set! You will find that the compiler only issues an 'assignment statement':

(defmethod emit* :set!
  [{:keys [target val env]}]
  (emit-wrap env (emits target " = " val)))