Arc Forumnew | comments | leaders | submitlogin
3 points by svetlyak40wt 3913 days ago | link | parent

Tried arcueid. It is unstable. For example, running this simple code:

  (thread (while t (prn "Still going")))
Ends very quickly with error like this:

  arcueid: cont.c:54: __arc_mkcont: Assertion `(((struct vmthread_t *)(((struct cell *)(thr))->_obj))->spr) > (((struct vmthread_t *)(((struct cell *)(thr))->_obj))->stkbase)' failed.
  zsh: abort      ~/tmp/arcueid-base/bin/arcueid


2 points by svetlyak40wt 3913 days ago | link

I've changed the test to count iterations:

  (thread (let i 0 (while t (prn "Still going: " i) (++ i))))
and it every time broke on 7270 iteration.

-----

2 points by svetlyak40wt 3913 days ago | link

Recursive code like this:

  (def my-loop ((o i 0)) (prn "Still going: " i) (my-loop (++ i)))
  (my-loop)
Performs much better. It fails only after 21799 iteration:

  Still going: 21799
  arcueid: env.c:83: __arc_mkenv: Assertion `(((struct vmthread_t *)(((struct cell *)(thr))->_obj))->spr) > (((struct vmthread_t *)(((struct cell *)(thr))->_obj))->stkbase)' failed.
  Still going: zsh: abort      ~/tmp/arcueid-base/bin/arcueid
:(

-----

1 point by akkartik 3913 days ago | link

I think all the errors you're seeing are due to running out of heap. How much memory do you have? Is there some per-process limit, perhaps to RLIMIT_AS?

Edit 35 minutes later. I can reproduce that it dies for me at the precise same iteration as you. And RLIMIT_AS is infinity, so that's not the issue. I've pinged the author for comment.

-----

2 points by svetlyak40wt 3911 days ago | link

Thank you. But now I think it would be wise not to complain about the issue on the forum, but rather to create an issue on the project's github. Will do it now.

Update: done — https://github.com/dido/arcueid/issues/60

-----

2 points by dido 3909 days ago | link

Well, thanks for the bug report. Well, I'll look into it when I have the time: the work which pays my bills has caught up with me once again and I don't have a lot of time to do hobby development. :)

-----

2 points by svetlyak40wt 3913 days ago | link

Well, actually, even without threading, arcueid running code:

  (let i 0 (while t (prn "Still going: " i) (++ i)))
Fails with exception:

  arcueid: cont.c:58: __arc_mkcont: Assertion `(((struct vmthread_t *)(((struct cell *)(thr))->_obj))->spr) > (((struct vmthread_t *)(((struct cell *)(thr))->_obj))->stkbase)' failed.
after 7266 iterations.

-----

2 points by dido 3909 days ago | link

The assertion error is a stack overflow. :) At present Arcueid makes use of a fixed-size stack within its virtual machine, and since the compiler still can't properly optimise tail recursion, your code overflows the stack.

-----

1 point by akkartik 3909 days ago | link

That was what I thought :) Is there a place where I can increase the size of the fixed stack? I looked for the limit in the code, but couldn't find it.

-----

3 points by dido 3908 days ago | link

src/vmengine.h:236:

#define TSTKSIZE 65536

Increase it as high as you like. :)

-----

1 point by akkartik 3908 days ago | link

Thanks!

Does it make sense to resize it on the fly when we discover we've overflowed the stack? Or are there potentially continuation pointers into the stack that would be non-trivial to track down?

-----

1 point by akkartik 3907 days ago | link

Yeah, no luck: https://github.com/akkartik/arcueid/commit/ae31b82540

-----

1 point by akkartik 3898 days ago | link

Possibly relevant: http://wingolog.org/archives/2014/03/17/stack-overflow

-----