[ruby-core:122496] [Ruby Bug#21401] ObjectSpace can't count Fibers after using a Ractor
From:
"rmosolgo (Robert Mosolgo) via ruby-core" <ruby-core@...>
Date:
2025-06-09 15:29:19 UTC
List:
ruby-core #122496
Issue #21401 has been reported by rmosolgo (Robert Mosolgo).
----------------------------------------
Bug #21401: ObjectSpace can't count Fibers after using a Ractor
https://bugs.ruby-lang.org/issues/21401
* Author: rmosolgo (Robert Mosolgo)
* Status: Open
* ruby -v: ruby 3.5.0dev (2025-06-09T14:38:29Z master f9966b9b76) +PRISM [x86_64-darwin22]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Hi, thanks for all your great work, Ruby crew!
I have a test in my project that uses `ObjectSpace.each_object(Fiber).count` to see how many Fibers have been started by my code. This test started failing when I added other tests using `Ractor`s. I was able to isolate it with this script:
```ruby
require "objspace"
f = Fiber.new { 1 + 1 }
GC.start
p ObjectSpace.each_object(Fiber).count
# => 2
Ractor.new { 1 + 1 }.take
p ObjectSpace.each_object(Fiber).count
# => 0 (should be 2)
# The fiber _is_ there!
p f
# #<Fiber:0x0000000100c568a8 ractor_fibers.rb:4 (created)>
```
It seems like `ObjectSpace` can't count fibers for some reason, but I expect it to return the number of Fibers in memory. Other classes like `Hash` and `String` are not affected.
It fails on Ruby 3.4.1 and 3.5-dev. I used:
- `ruby 3.5.0dev (2025-06-09T14:38:29Z master f9966b9b76) +PRISM [x86_64-darwin22]`
- `ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-darwin22]`
Please let me know if I can help with anything else in tracking down this bug. Thanks again!
--
https://bugs.ruby-lang.org/
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