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.
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.
People fixate on stack size, but memory fragmentation is what bites as fiber counts grow, and actors dodge some of that at the cost of more message-passing overhead plus debugging hell once state gets hairy. Atomics or explicit channels cost cycles that never show up in naive benchmarks. If you need a million concurrent 'things' and they are not basically stateless, you're already in Erlang country, and the rest is wishful thinking.
Actors are a model, I have no clue why you're saying that there is a particular memory cost to them on real hardware. To me, you can implement actors using fibers and a postbox.
I've no idea what the majority of programmers know or do not know about, but async logging isn't unknown and is supported by libraries like Log4j.
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
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.
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.
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?
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.
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.
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.
People fixate on stack size, but memory fragmentation is what bites as fiber counts grow, and actors dodge some of that at the cost of more message-passing overhead plus debugging hell once state gets hairy. Atomics or explicit channels cost cycles that never show up in naive benchmarks. If you need a million concurrent 'things' and they are not basically stateless, you're already in Erlang country, and the rest is wishful thinking.
Actors are a model, I have no clue why you're saying that there is a particular memory cost to them on real hardware. To me, you can implement actors using fibers and a postbox.
I've no idea what the majority of programmers know or do not know about, but async logging isn't unknown and is supported by libraries like Log4j.
I remember Joe Armstrong saying something like 2kB in his talks, for an Erlang process. That's 1/128 of 256kB.
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
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.
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.
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.
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?
Green threads are cooperative threads. Preemption requires ability to handle hardware interrupts, which are typically handled by the OS.
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.
Huh, you're right.
Apparently it's still considered experimental (even though Google uses it in production) so it's not in the User Manual. There's this: https://github.com/sbcl/sbcl/blob/master/doc/internals-notes...
I really thought this was gonna be a sick material science paper. Still cool though
Serious question - I thought LLMs were bad at balancing parentheses?
They are much better these days.
SBCL - Steel Bank Common Lisp
They should be called Anthony Green Threads. Seriously though, great to see.