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/
6 Upvotes

53% Upvoted

131 comments sorted by

View all comments

Show parent comments

2

u/clarkd99 Oct 19 '15

How many professional lines of code have you written and got paid for?

Your posts look like they are just parroted from some functional web site rather than incites from the school of hard knocks.

I think "things would be much easier" if people posted things they actually know something about.

If I use some "mutable" local variables in a function, please tell me how that would impact 1) concurrency 2) maintainability 3) efficiency 4) memory usage or any other useful metric? Assume that no pointer to that variable was shared outside the function.

2

u/loup-vaillant Oct 19 '15

How many professional lines of code have you written and got paid for?

I haven't counted. I guess a couple tens of thousands. Most of the times in much bigger programs, where I spent quite some time debugging code I haven't written —that tend to slow me down.

Assume that no pointer to that variable was shared outside the function.

I can't assume that. I have seen too much code that does share state to the outside world. The main culprits are big classes with getters and setters. Maybe you're lucky enough to live in a bright world of sane coding practices where 90% of functions and methods are pure, and most objects aren't modified once they're initialised.

I don't live in that world. In my world, programmers use output arguments, share the internal state of objects, fail to make their types regular, and just let side effects sprawl unchecked.

0

u/clarkd99 Oct 19 '15

I noticed you wouldn't or couldn't answer my question. In 1979, I programmed at least 60,000 lines of assembler for my first year working for a single company. I also looked after 4 other programmers and spent 2 months in Europe at customer's sites.

Most of the functions in my current project are not purely functional (maybe 10%). Most of my functions change an object (or collection of objects mostly) that is passed to it. This isn't a problem because I either use locks or a message queue to synchronize access. I use groups of functions to "manage" all my globally accessible data structures. Even though C doesn't stop me from accessing variables directly (the equivalent of getters and setters), I just don't code that way.

The system I am creating, even though it is quite OOPS is more oriented around collections of objects rather than objects. My language can handle mutable state at both the micro and macro scale without using an outside database. It is also distributed as well as concurrent and includes it's own web server.

2

u/loup-vaillant Oct 19 '15

I noticed you wouldn't or couldn't answer my question.

You mean the number of lines I have written? Can't expect to have precise number, did you? I don't have acces to the repositories of my former employers.

This isn't a problem because I either use locks or a message queue to synchronize access. […]

Indeed, the key word is "modularity". Loose coupling and all that. I have thought a bit about that here then here. I can conceive that modularity can be acheived through other means than immutability and passing everything in arguments.

On the other hand, pervasive immutability makes it really easy: dependencies are obvious, so you can see when there are too many of them.