Bug #21149: Strange behavior of ObjectSpace.each_object after Ractor.new

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-linux]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[wanabe (_ wanabe)]

I found the strange behavior of ObjectSpace.each_object.
It misses some objects after Ractor.new.

$ ruby -ve 'class Foo; end; foo = Foo.new; Ractor.new do buz = Foo.new end.take; bar = Foo.new; p [ObjectSpace.each_object(Foo).to_a, foo.class, bar.class]'
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-linux]
-e:1: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
[[], Foo, Foo]

Of course it works well without Ractor.new.

$ ruby -ve 'class Foo; end; foo = Foo.new; bar = Foo.new; p [ObjectSpace.each_object(Foo).to_a, foo.class, bar.class]'
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-linux]
[[#<Foo:0x00007fa84f4b26d0>, #<Foo:0x00007fa84f4b27c0>], Foo, Foo]

[nobu (Nobuyoshi Nakada)]

Interesting.
It seems irrelevant what is done in the new Ractor.
Even if the block is empty, the result is same.

[luke-gru (Luke Gruber)]

Yes, this is a known bug. Currently, objects don't record which ractor they belong to. Therefore, after you start new Ractor Ruby can't know if it should yield an unshareable object to ObjectSpace.each_object, because it would violate Ractor safety if it yielded it and that object didn't belong to the ractor that called each_object. You can see that shareable objects (like if you froze it) are yielded.

You can see the code here: https://github.com/ruby/ruby/blob/master/gc.c#L1526-L1528

From what I remember, this is documented somewhere but I could be wrong. If it's not documented, it should be.

[wanabe (_ wanabe)]

• Status changed from Open to Rejected

Thank you. I forgot to search existing issues before opening the ticket. Now I can see many related tickets:

• [Feature #17270] ObjectSpace.each_object should be restricted on multi-Ractors
• [Bug #17360] Objects disappear from ObjectSpace after using Ractor
• [Bug #19387] Issue with ObjectSpace.each_objects not returning objects after starting a ractor

I will reject this #21149 as duplicated.

[wanabe (_ wanabe)]

• Related to Feature #17270: ObjectSpace.each_object should be restricted on multi-Ractors added

[wanabe (_ wanabe)]

• Is duplicate of Bug #17360: Objects disappear from ObjectSpace after using Ractor added
• Is duplicate of Bug #19387: ObjectSpace.each_objects only returns shareable objects after starting a Ractor added