27 Dec
2023
27 Dec
'23
9:53 p.m.
Issue #20089 has been updated by ioquatix (Samuel Williams).
Transfer is uni-directional and keeps no state about the caller. It's up to the caller
to implement its own control flow if preferred. It's a low level operation which must
be used more carefully.
```ruby
manager = Fiber.new do
worker = Fiber.new do
puts "2. Begin Worker"
manager.transfer
Fiber.current.kill
puts "This should never print -- killed"
ensure
manager.transfer
end
puts "1. Transfer to Worker"
worker.transfer
puts "3. Killing Worker"
worker.transfer
puts "4. Finished manager"
end
manager.transfer
puts "5. Finished script"
```
By explicitly adding the flow control, we can achieve your desired output. Hope this
helps.
----------------------------------------
Bug #20089: Fiber#kill transfers to root fiber
https://bugs.ruby-lang.org/issues/20089#change-105895
* Author: rmosolgo (Robert Mosolgo)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-darwin22]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
I was hoping to use `Fiber#kill` to clean up formerly `.transfer`-d Fibers and work around
https://bugs.ruby-lang.org/issues/20081, but I found that `Fiber#kill` has a similar
control flow jump behavior. Is this on purpose, or a bug?
Here's a script to test the behavior:
```ruby
manager = Fiber.new do
worker = Fiber.new do
puts "2. Begin Worker"
manager.transfer
puts "This should never print -- killed"
end
puts "1. Transfer to Worker"
worker.transfer
puts "3. Killing Worker"
worker.kill
puts "4. Finished manager"
end
manager.transfer
puts "5. Finished script"
```
I expected items `1` through `5` to be printed in order, but in fact, `4` is never
printed:
```
$ ruby fiber_transfer_test.rb
1. Transfer to Worker
2. Begin Worker
3. Killing Worker
5. Finished script
```
It seems like `worker.kill` is transferring control to the top-level fiber instead of
giving it back to `manager`.
I also tried having the thread kill _itself_, hoping it would return to the fiber that
originally `.transfer`ed to it, but it also seems to jump out:
```ruby
manager = Fiber.new do
worker = Fiber.new do
puts "2. Begin Worker"
manager.transfer
Fiber.current.kill
puts "This should never print -- killed"
end
puts "1. Transfer to Worker"
worker.transfer
puts "3. Killing Worker"
worker.transfer
puts "4. Finished manager"
end
manager.transfer
puts "5. Finished script"
```
Prints:
```
1. Transfer to Worker
2. Begin Worker
3. Killing Worker
5. Finished script
```
--
https://bugs.ruby-lang.org/