[ruby-core:117461] [Ruby master Bug#20414] `Fiber#raise` should recurse to `resumed_fiber` rather than failing.
From:
"ioquatix (Samuel Williams) via ruby-core" <ruby-core@...>
Date:
2024-04-07 14:26:04 UTC
List:
ruby-core #117461
Issue #20414 has been updated by ioquatix (Samuel Williams).
With the proposed change, the following program:
```ruby
root_fiber = Fiber.current
f1 = Fiber.new do
puts "f1 enter"
root_fiber.transfer
puts "f1 exit"
ensure
puts "f1 ensure"
end
f2 = Fiber.new do
puts "f2 enter"
f1.resume
puts "f2 exit"
ensure
puts "f2 ensure"
end
f2.transfer
begin
puts "raise"
f2.raise(Interrupt)
rescue Interrupt => e
puts "rescue Interrupt"
end
```
... generates the following output:
```
f2 enter
f1 enter
raise
f1 ensure
f2 ensure
rescue Interrupt
```
----------------------------------------
Bug #20414: `Fiber#raise` should recurse to `resumed_fiber` rather than failing.
https://bugs.ruby-lang.org/issues/20414#change-107848
* Author: ioquatix (Samuel Williams)
* Status: Open
* Assignee: ioquatix (Samuel Williams)
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
The following program will fail with `FiberError`, and is difficult to properly clean up:
```ruby
root_fiber = Fiber.current
f1 = Fiber.new do
root_fiber.transfer
end
f2 = Fiber.new do
f1.resume
end
f2.transfer
f2.raise("error") # => `raise': attempt to transfer to a resuming fiber (FiberError)
```
This program deliberately set's up a scenario where `f2` is resuming `f1`. Trying to raise an exception on `f2` is impossible, because the only way control flow can return to it, is when `f1` yields or exits.
We can avoid this problem, by raising the exception on f1, and we can do this automatically using the following logic:
```c
static VALUE
fiber_raise(rb_fiber_t *fiber, VALUE exception)
{
// Add this recursive step:
if (fiber->resuming_fiber) {
return fiber_raise(fiber->resuming_fiber, exception);
}
// Existing code ...
else if (FIBER_SUSPENDED_P(fiber) && !fiber->yielding) {
return fiber_transfer_kw(fiber, -1, &exception, RB_NO_KEYWORDS);
}
else {
return fiber_resume_kw(fiber, -1, &exception, RB_NO_KEYWORDS);
}
}
```
This makes `Fiber#raise` much more robust and useful for the purpose of stopping fibers, without knowing exactly what they are doing.
--
https://bugs.ruby-lang.org/
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