Hacker News Reader

Comment by BlanketLogic | Hacker News Reader

Very informative. Thank you.

Anyone here has any experience with the GCs of Allegro or LispWorks or any other commercial Lisp implementations?

LispWorks has a lot of features in its GC. Years ago it was used in a demanding telco application, an ATM switch. It was also used on a space mission experiment. Generally the runtime is very very nice.

Franz Inc uses Allegro CL in a large database. They tuned the GC quite a bit for that. But there were also other GC demanding applications on Allegro CL, for example in CAD and 3D design. They are now working on a concurrent GC, something which is still rare in the Lisp world.

Why are concurrent GCs rare?

I am guessing[1] that GCs are easier to code correctly without the concurrency and that a GC language is already expected to be slower so it doesn't make sense to do a concurrent GC. Also possibly, the language doesn't support concurrency well. Like a Python or Ruby.

[1] just an educated guess. I have no real knowledge of GCs other than skimming how they work in articles and runtime/language docs.

Mostly because there are very very few people in the world who are able to develop such a complex thing for Lisp (or similar runtimes). Since the market is relatively small and many applications are not overly concurrent, there is very little money to support the development.

are there many platforms, besides JVM and .Net, that have good-quality concurrent GCs?

The Erlang Vm (BEAM), is another one at least.

It doesn't actually implement concurrent GC, although what it does implement is far simpler and has a similar effect (low latencies) as concurrent GC.

Each Erlang process has a separate heap that is collected independently; because the process heap is usually small a stop-the-process collection does not take much time.

The downside is that sending messages between processes requires copying all the data that is sent between process heaps.

Who used lispworks in an ATM switch? My very first job was working on ATM/IMA switches.

Lucent. The switching nodes were running LispWorks and the control system was running Allegro CL + OO database. That's quite some time ago... ;-)

I've worked a lot with LispWorks and tuning the gc had the same method of programmatically calling a full GC after every N operations. We also found setting the gc threshold to high amount helped a bunch.

Supposedly they have a concurrent GC in the works but I haven't played with it.

Thanks.

> I've worked a lot with LispWorks and tuning the gc had the same method of programmatically calling a full GC after every N operations.

What is "full GC", here? Do you mean, even the "older" generations? (Assuming Lispworks also has generational GC a la sbcl)

In other words, Would it have helped if the implementation was a mark-compact rather than generational?

We normally used

http://www.lispworks.com/documentation/lw60/LW/html/lw-712.h...

with the full set to nil.

Reply on news.ycombinator.com