Whats the cost of recursivity in Ruby?

Question

I have a ruby service that keeps running forever and I wonder whats the cost of recursivity. When I ctrl-c the service after some time, I get the following error printed:

^Cff.rb:169:in `sleep': Interrupt
    from ff.rb:169:in `fetch'
    from ff.rb:170:in `fetch'
    from ff.rb:187:in `fetch'
    from ff.rb:180:in `fetch'
    from ff.rb:170:in `fetch'
    from ff.rb:187:in `fetch'
    from ff.rb:177:in `fetch'
    from ff.rb:170:in `fetch'
 .... and continue for each recursive call

This makes me wonder if this has a memory cost or if it eventually will fail? Is it bad to use recursive in Ruby like this? Would another solution be better? Ty.

Looks like you need a loop instead of a recursive call. Recursion is not intended to run deeper forever, and it doesn't matter if it is Ruby, C or whatever. — sidyll, Sep 24 '11 at 13:08
@JacobRelkin It's on [wiktionary](http://en.wiktionary.org/wiki/recursivity) so it must be true ;) — Dave Newton, Sep 24 '11 at 13:08
@grm Sure, there's a memory cost--the stack keeps growing. That doesn't make recursion fundamentally bad, though--it's only bad it there's no "stop it!" condition. Doesn't mean you should be using recursion in *this* situation, though; we don't know. — Dave Newton, Sep 24 '11 at 13:11
You've heard of the expression "select is not broken", right? — Andrew Grimm, Sep 24 '11 at 14:13
For some reason I assumed it had no cost in ruby and was surprised. Thanks for your help! — grm, Sep 24 '11 at 16:10

score 1 · Accepted Answer · answered Sep 24 '11 at 13:09

1

AFIAK, Ruby never turns tail call recursion into loops. If you keep calling a function recursively, eventually you'll run out of memory.

answered Sep 24 '11 at 13:09

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It's possible to make YARV support tail call optimization. See http://stackoverflow.com/questions/824562/does-ruby-perform-tail-call-optimization/824831#824831 – Andrew Grimm Sep 24 '11 at 14:10

Whats the cost of recursivity in Ruby?

1 Answers1