mattmower
I’ve twice now created a parser that hangs, that is given a finite input string a call to parse_xxx it never returns and the beam.smp process is consuming ~100% of a core.
I’m usually making a small, seemingly innocuous, change to the string being parsed that causes the hang.
Should this actually be possible?
Thanks.
Matt
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mattmower
As a further note here, in the (much simpler) parser combinator library I built called Ergo I have implemented cycle detection and the parser will automatically halt with a trace of the history of rules. A bit primitive right now but I’ve found it useful when playing with a new grammar.
mattmower
Thank you Jose.
I had read that but hadn’t appreciated what it was saying. I do have a few cases where
repeatandoptionalget combined and I suspect this is what is happening.Part of the problem is that I find my error handling strategy is “fiddle with it a bit” because I find the error information difficult to work with. Any guidance about (or good examples of) that would be much appreciated.
Thanks.
Matt
josevalim
Yes, it can loop forever. Usually the culprit is
repeat. Its docs has warnings on when such cases may happen:If you are still running into loops, then a minimal parser that reproduces the failure would be welcome.
trarbr
I have seen it hang if I wrote a parser that would infinitely recurse. Unfortunately I can’t recall the details, but I fixed it by changing my parser. If you can’t find any infinite recursion happening, it might be a bug in NimbleParsec?
Anyway, if you want to guard against the parser hanging, you might want to wrap the parsing in a Task