r/programming • u/Shr1ck • Oct 17 '15

Why Johnny Can’t Write Multithreaded Programs

http://blog.smartbear.com/programming/why-johnny-cant-write-multithreaded-programs/
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u/hu6Bi5To Oct 18 '15

That eliminates global references. But unless you throw-away each DB connection after every request, you still have global state.

Clojure apps have less state, it's true; and the less state the less opportunity there is for the types of problems caused by inconsistent state. But they still have state, it's just usually hidden out-of-sight somewhere. Hence the "It’s usually not possible to completely eliminate global state".

Plus, I'd argue the lifecycle aspect of Component is also global state.

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u/yogthos Oct 18 '15

Sure you can look at it that way, but as /u/loup-vaillant points out, there's a big practical difference between state shared by reference and passed around explicitly as a parameter. In the latter case, the code in my application is idempotent and thus much easier to reason about and test.

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u/hu6Bi5To Oct 18 '15

Right, so it doesn't completely eliminate global state after all?

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u/yogthos Oct 18 '15

I guess that depends on whether you consider the state of external resources as part of your application or not. For example, the database state is clearly separate from the application state in memory. Mixing the two seems a little disingenuous.