From: "ioquatix (Samuel Williams) via ruby-core" <ruby-core@...>
Date: 2026-07-01T22:45:42+00:00
Subject: [ruby-core:125905] [Ruby Bug#20081] Transfered Fiber doesn't return to Fiber that started it

Issue #20081 has been updated by ioquatix (Samuel Williams).


I think the crux of the issue here is that there is no way for a user to a final transfer (or raise that transfers) that goes back to a specific fiber, but it probably should be possible.

```
fiber = Fiber.new do
  # Do stuff
  
  # Final transfer is back to scheduler:
  scheduler.transfer
end

# from scheduler
fiber.transfer
fiber.alive? # false
```

Basically, in order to exit a fiber (for it to become dead) you have to rely on it exiting, but you don't have control over where it goes. I'm still not sure what the right solution here is but the above PR was just an experiment.

----------------------------------------
Bug #20081: Transfered Fiber doesn't return to Fiber that started it
https://bugs.ruby-lang.org/issues/20081#change-117840

* Author: rmosolgo (Robert Mosolgo)
* Status: Open
* ruby -v: ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-darwin22]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
Hi! I'm trying to figure out how to make sure that Fibers started with `.transfer` end up _terminated_, not just suspended. (If they're suspended, Rails thinks they're still alive, and they continue to hold onto database connections, see: https://github.com/rmosolgo/graphql-ruby/issues/4739#issuecomment-1866930914.)

So, I'm looking for way to make sure that any Fiber I start with `.transfer` will be properly terminated. But what I noticed is that when a transfer-based Fiber terminates, it gives control back to the top-most Fiber, not the Fiber which transfered to it. Is this intended? Here's a script to replicate the issue: 


```ruby
manager = Fiber.new do
  parent = Fiber.current
  worker = Fiber.new do
    puts "2. Begin Worker"
    parent.transfer
    puts "4. End Worker"
  end

  puts "1. Transfer 1"
  worker.transfer
  puts "3. Transfer 2"
  worker.transfer
  puts "5. Finished manager"
end

manager.transfer
puts "6. Finished script"
```

I expect the steps to print in order: 

```
1. Transfer 1
2. Begin Worker
3. Transfer 2
4. End Worker
5. Finished manager
6. Finished script
```

But instead, `5. ...` is skipped: 

```
1. Transfer 1
2. Begin Worker
3. Transfer 2
4. End Worker
6. Finished script
```

I think that's because my `worker` fiber terminates and passes control back to the top-level Fiber. 

Should it have passed control back to the `manager`? Or is there another way to make sure `worker` is terminated, and `manager` gets control?



-- 
https://bugs.ruby-lang.org/
______________________________________________
 ruby-core mailing list -- ruby-core@ml.ruby-lang.org
 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
 ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/