Hacker News Reader

Comment by M_Bakhtiari | Hacker News Reader

Is the spawning overhead comparable to that of Erlang's BEAM?

The performance tradeoffs are quite different, because this library uses the unmodified Smalltalk virtual machine that underlies Squeak. I would guess spawning is quite fast, because it is more-or-less just a few object allocations (plus a couple of linked list manipulations), but I have not made any serious measurements of performance of the system. Also, the Squeak VM has (IIRC) limited ability to make use of true parallelism.

A second tradeoff is in terms of flexibility: this is an ordinary (and fairly small) Smalltalk library, and so can be quickly sculpted into variations on the theme of Actors. Making similar modifications to Erlang would be very expensive. I aim to use this library as a foundation for experimenting with Syndicate-style ideas (https://syndicate-lang.org/) in a pervasively OO setting.

> Also, the Squeak VM has (IIRC) limited ability to make use of true parallelism.

The Squeak VM is single-threaded, OS-wise, so it's just green threads. I don't even honestly remember to what extent its green threads are preemptive; I do remember that anything hitting C would pause other threads until it concluded, though, which made it really important to make sure that e.g. your database driver was 100% Smalltalk so it wouldn't lock the VM constantly.

Kinda. The VM executes Smalltalk on a single thread (interpreting or running JIT-compiled code). At the Smalltalk level, the unit of concurrency is called a "process". Processes are assigned priorities. Processes with higher priority preempt processes of lower priority, but processes of the same priority are cooperative.

So yes, "green threads". However, the VM does run multiple OS threads. When a Smalltalk process does IO, that gets performed on a different OS thread by the VM and the calling Smalltalk process is blocked, which lets another Smalltalk process get scheduled.

You could do that trick for things like calling ODBC or computationally expensive C code, but if you just call single-threaded C code directly, yeah, it'll block all Smalltalk processes until it returns.

Syndicate seems very cool! Do you know if it's used by anyone or is it more of a research project at this stage? Am I right that the pattern seems very similar to re-frame [0] in Clojurescript? It seems like it might be an excellent way to develop web apps, especially since I see there's a javascript version as well.

[0] https://github.com/Day8/re-frame

It is still a research project, though I am working on a new implementation that brings it up to production standards.

Re-frame does look similar, but Syndicate is general in the same way that the Actor model is general; DOM support and other "I/O devices" are bolt-on drivers, not built in to the core.

Syndicate does make a nice way to develop web apps; for example, the whatsapp-like chat app here https://github.com/tonyg/syndicate/tree/master/examples/webc... shows a few of the ideas, though it's only prototype/experimental quality. The new implementation ought to be suitable for making such applications "for real". See also the handful of in-browser demos, which naturally focus on web-ish things: http://syndicate-lang.org/examples/.

The Racket implementation has been used to implement not only the server side of the webchat app, but also a TCP/IP stack [1], an IRC server [2], and a side-scrolling platform game [3].

I'm afraid that there's very little documentation available (it is still a research project, after all!). You can read more about the ideas behind it here, though: http://syndicate-lang.org/tonyg-dissertation/.

[1] https://github.com/tonyg/syndicate/tree/master/examples/nets...

[2] https://github.com/tonyg/syndicate/tree/master/examples/ircd

[3] https://github.com/tonyg/syndicate/blob/master/examples/plat...

Thanks I will check out those examples! Again, this looks really cool. I just started playing a bit with Racket, so this is nice to dive into.

Reply on news.ycombinator.com