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SBCL Fibers – Lightweight Cooperative Threads

256Kb stack per Fiber is still insane overhead compared to Actors. I guess if we survey programming community, I’d guesstimate that less than 2% of devs even know what the Actor model is, and an even smaller percentage have actually used it in production.

Any program that has at least one concurrent task that runs on a thread (naturally they’ll be more than one) is a perfect reason to switch to Actor programming model.

Even a simple print() function can see performance boost from running on a 2nd core. There is a lot of backround work to print text (parsing font metrics, indexing screen buffers, preparing scene graphs etc) and its really inefficient to block your main application while doing all this work while background cores sit idle. Yet most programmers dont know about this performance boost. Sad state of our education and the industry.

an hour agosmallstepforman

256k is just's just a placeholder for now. The default will get reduced as we get more experience with the draft implementation. The proposal isn't complete yet.

39 minutes agoatgreen

Fibers are primarily when you have a problem which is easily expressible as thread-per-unit-of-work, but you want N > large. They can be useful for eg a job system as well, and in that case the primary advantage is the extremely low context switch time, as well as the manual yielding

There are lots of problems where I wouldn't recommend fibers though

an hour ago20k

I strongly recommend having a look at the mailing list to get some context:

https://sourceforge.net/p/sbcl/mailman/sbcl-devel/thread/CAF...

and

https://sourceforge.net/p/sbcl/mailman/sbcl-devel/thread/CAC...

This will certainly speak to some people taking part in some of the more controversial discussions taking place on HN recently, to put it mildly.

2 hours agonothrabannosir

Hmm, must have missed that ; tried to find. There was a SBCL discussion a few days ago but didn't read much controversial things in that? I'm a fanboy though so possibly i'm blind to these things.

2 hours agoanonzzzies

I personally like the name fiber better than green threads. But everywhere I’ve worked in user space cooperative threads, it’s always been green threads.

7 hours agomatthewfcarlson

They are different things perhaps? Fibers imply strict cooperative behaviour; I have to explicitly “yield” to give the other fibers a go, green threads are just runtime managed threads?

4 hours agolll-o-lll

I really thought this was gonna be a sick material science paper. Still cool though

an hour agotheParadox42

Is there a similar document for the memory arena feature? I tried searching the official documentation, but found scant references and no instructions on how and when to use it.

4 hours agoHexDecOctBin

Serious question - I thought LLMs were bad at balancing parentheses?

2 hours agolukasb

They are much better these days.

38 minutes agoatgreen

SBCL - Steel Bank Common Lisp

3 hours agopestatije

They should be called Anthony Green Threads. Seriously though, great to see.