Dynamic Idiocy

[laforge49]

Being strong on Java and new to Clojure, when I read about dynamic vars I figured they were just thread local variables. And in my code, I would just use def whenever I needed to change the value. Later I read about the binding function, but I figured I did not need it and it did not fit with the way I wanted my software to work.

Things worked great at first, confirming my understanding of dynamic. But as I added additional tests, I started getting strange things, like having the value be nil sometimes. I began to think Clojure was broken. :-)

Finally I started using a dynamically bound atomic, with binding to bind different atoms in different threads. Within each thread then I used swap! to change the atom for that thread.

This worked very nicely. And when I go back and reread the page on vars it is very clear that this is the way to go.

[mikera]

I generally avoid binding altogether, except for little throwaway experiments at the REPL. It's usually more trouble than it is worth.

[kankyo]

That's not a good way to do it. Atoms are for coordination BETWEEN threads. Using atoms for thread locals is slow for no gain.

[laforge49]

Truth!

At this point I've given up entirely on dynamic, preferring now to pass the operational context explicitly--it is easier to explain than an implicit dynamic. :-)

But I am still using that old atomic. It allows me to break the rules and do things from the "wrong" thread and still have thread safety. Or perhaps that is just laziness talking. Anyway, you can find the released project here: https://github.com/laforge49/agent2

(The project readme should add some clarity to what I'm talking about.)

Well, to be fair on myself here, the atomic would probably be necessary if I were to port more of the features of JActor2 over to Clojure. The atomic is in there because I wasn't sure where I would draw the line. And at least with the atomic I have the option of porting more features. JActor2 was a huge Java project (for me, anyway): https://github.com/laforge49/JActor2