[ruby-core:53462] [ruby-trunk - Feature #7791] Let symbols be garbage collected

Issue #7791 has been updated by Student (Nathan Zook).


kstephens (Kurt  Stephens) wrote:
> Student (Nathan Zook) wrote:
> > Questions: 
> > 1) How certain are you that this covers all of the cases?
> 
> With the unit and functional tests that already exist.  What cases do you have in mind?
> 

The existing test cases all assume that symbol behaves the way that it currently does.  There are tests to check a against certain deviations, but not all possible ones.  This is what I meant earlier about the probability that such a change will introduce bugs.  We absolutely cannot rely on the current test suite to guarantee the safety/sanity of a change of this magnitude.


> > 2) In order to actually recover the memory, the symbol table has to be walked each time a symbol is created.  What are the implications of this?
> 
> The symbol table only has to be walked during sweep and can be done incrementally.

That assumes that you reassign all symbols after a gap.  DANGER, WILL ROBINSON!!! DANGER!!!

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Feature #7791: Let symbols be garbage collected
https://bugs.ruby-lang.org/issues/7791#change-37645

Author: rosenfeld (Rodrigo Rosenfeld Rosas)
Status: Feedback
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: next minor


Lots of Denial-of-Service security vulnerabilities exploited in Ruby programs rely on symbols not being collected by garbage collector.

Ideally I'd prefer symbols and strings to behave exactly the same being just alternate ways of writing strings but I'll let this to another ticket.

This one simply asks for symbols to be allowed to be garbage collected when low on memory. Maybe one could set up some up-limit memory constraints dedicated to storing symbols. That way, the most accessed symbols would remain in that memory region and the least used ones would be reclaimed when the memory for symbols is over and a new symbol is created.

Or you could just allow symbols to be garbage collected any time. Any reasons why this would be a bad idea? Any performance benchmark demonstrating how using symbols instead of strings would make a real-world software perform much better?

Currently I only see symbols slowing down processing because people don't want to worry about it and will often use something like ActiveSupport Hash#with_indifferent_access or some other method to convert a string to symbol or vice versa...


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