ruby-core

Issue #15088 has been reported by william101 (William Tabi).

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Bug #15088: Leaky behaviour when GC disabled
https://bugs.ruby-lang.org/issues/15088

* Author: william101 (William Tabi)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.4p296 (2018-03-28 revision 63013) [x86_64-darwin17]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
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Hello

I've observed some leaky behaviour when creating dynamic Symbols ("string".to_sym) when GC is disabled. Creating a dynamic symbol after running `GC.disable` creates an extra string allocation that isn't garbage collected when GC is enabled later on in the code. 

Based on https://bugs.ruby-lang.org/issues/9634 and https://bugs.ruby-lang.org/issues/7791,  I would have expected all the memory allocated by #to_sym to be GC'ed 


I can reproduce this using

~~~ ruby
# frozen_string_literal: true

require 'objspace'

GC.start

puts"Before - All: #{ObjectSpace.each_object.count}"
puts"Before - Symbols: #{Symbol.all_symbols.size}"

GC.start
GC.disable

100_000.times do |i|
  "to_sym_#{i}".to_sym
end

GC.enable
GC.start

puts"After - All: #{ObjectSpace.each_object.count}"
puts"After - Symbols: #{Symbol.all_symbols.size}"

~~~

This is the output:

with latest master v2.6.0-dev
~~~
$ RBENV_VERSION=2.6.0-dev ruby -v /tmp/test.rb
ruby 2.6.0dev (2018-09-07 trunk 64657) [x86_64-darwin17]
Before - All: 10740
Before - Symbols: 3206
After - All: 110739
After - Symbols: 3206
~~~

with ruby v2.2.2
~~~
$ RBENV_VERSION=2.2.2 ruby -v /tmp/test.rb
ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-darwin17]
Before - All: 6342
Before - Symbols: 2536
After - All: 106344
After - Symbols: 2536
~~~

Would anyone know if this is expected behaviour or a bug?




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