From: "ioquatix (Samuel Williams) via ruby-core" <ruby-core@...>
Date: 2023-12-26T11:34:41+00:00
Subject: [ruby-core:115903] [Ruby master Bug#20082] Killing fibers across threads: unexpected exception

Issue #20082 has been updated by ioquatix (Samuel Williams).


> Raises FiberError if called on a fiber belonging to another thread.

I agree the error is a little confusing, but the reality is it's probably okay.

"in `kill': attempt to resume a resumed fiber (double resume) (FiberError)"

You are literally reaching across into a fiber which is currently resumed and executing sleep. This is a text book definition of a double resume.

To get the error message I imagine you are after:

```ruby
fibers = []

Thread.new {
  f = Fiber.new { Fiber.yield }
  f.resume
  fibers << f
}.join

fibers.last.kill
```

> without resuming, the code doesn't see any problem at all (despite the claim about killing other thread's fibers):

A fiber is lazily constructed according to the first thread it is resumed on. So, this behaviour looks okay to me.

----------------------------------------
Bug #20082: Killing fibers across threads: unexpected exception
https://bugs.ruby-lang.org/issues/20082#change-105858

* Author: zverok (Victor Shepelev)
* Status: Open
* Priority: Normal
* Assignee: ioquatix (Samuel Williams)
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
For providing the example in a changelog, I tried to imitate killing fibers belonging to other threads.
Documentation [claims](https://docs.ruby-lang.org/en/master/Fiber.html#method-i-kill)

> Raises FiberError if called on a fiber belonging to another thread.

So, I created this artificial example to check how it works:
```ruby
fibers = []

Thread.new {
  f = Fiber.new { (1..).each { sleep(0.1) } }
  fibers << f
  f.resume
}
sleep(0.1) # to make sure the thread has started

fibers.last.kill
```
The example indeed fails with `FiberError`, but the error message is confusing:
```
in `kill': attempt to resume a resumed fiber (double resume) (FiberError)
```

Is this an expected message for such case? Or am I misunderstanding something?



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