Bug #10620: #define_singleton_method keeps object from being garbage collected

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: 2.1.5
• Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN

[[e-mail] (Sean Dilda)]

After using #define_singleton_method on an object, the object is never garbage collected

Sample code:
#!/usr/bin/env ruby

obj = Object.new
obj_id = obj.object_id
obj = nil

GC.start
GC.start
GC.start
GC.start
begin
ObjectSpace._id2ref obj_id
puts "GC failed, object still exists"
rescue RangeError
puts "GC worked"
end

obj = Object.new
obj.define_singleton_method(:f) { "F" }
obj_id = obj.object_id
obj = nil

GC.start
GC.start
GC.start
GC.start
begin
ObjectSpace._id2ref obj_id
puts "GC failed, object still exists"
rescue RangeError
puts "GC worked"
end

This outputted:
GC worked
GC failed, object still exists

The object without the singleton method was cleaned up properly, the object with defined_singleton_method used never got cleaned up.

[normalperson (Eric Wong)]

Try the following infinite loop, I see stable memory usage:

loop do
  obj = Object.new
  obj.define_singleton_method(:f) { "F" }
end

Not even multiple calls to GC.start can guarantee an object is
collected, as the current Ruby GC is conservative and not precise.
Precise GC should solve the problem, but that is a lot of work
(and we'd still need a conservative part for 3rd party extensions
for years)

[[e-mail] (Sean Dilda)]

Thanks for the quick response.

I tried your code and saw what you did.. it cleans up the objects, just a lot slower than I expected.
Please feel free to close out this bug. I'd do so, but I'm not seeing the option.

[shugo (Shugo Maeda)]

• Status changed from Open to Closed

[usa (Usaku NAKAMURA)]

• Status changed from Closed to Rejected