From: samuel@...
Date: 2020-12-06T02:02:17+00:00
Subject: [ruby-core:101255] [Ruby master Bug#17331] Let Fiber#raise work	with transferring fibers

Issue #17331 has been updated by ioquatix (Samuel Williams).

Backport set to 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
Tracker changed from Feature to Bug

I consider this a bug fix rather than an interface change. I'll review it and consider merging it today.

----------------------------------------
Bug #17331: Let Fiber#raise work with transferring fibers
https://bugs.ruby-lang.org/issues/17331#change-88932

* Author: nevans (Nicholas Evans)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
It would be useful to use `raise` on transferring fibers just as we can with yielding fibers.

I've added a `transfer` kwarg, so it is not automatic; the caller must know how to handle the fiber.  If you call a yielding fiber with `transfer: true` or a transferring fiber without `transfer: true`, a `FiberError` will be raised. Resuming fibers still raise a `FiberError`.

```ruby
yielding_fiber.raise "message"
# => resumes and raises from the last Fiber.yield

transferring_fiber.raise "message", transfer: true
# => transfers and raises from the last fiber.transfer

resuming_fiber.raise "message"
# => raises FiberError
```

Implementation: https://github.com/ruby/ruby/pull/3783


I also implemented a second version that implicitly and automatically selects `rb_fiber_transfer_kw` for transferring fibers and `rb_fiber_resume_kw` for yielding fibers. The implicit version also raises `FiberError` on resuming fibers.


```ruby
yielding_fiber.raise "message"
# => resumes and raises from the last Fiber.yield

transferring_fiber.raise "message"
# => transfers and raises from the last fiber.transfer

resuming_fiber.raise "message"
# => raises FiberError
```

Alternate implicit implementation: https://github.com/ruby/ruby/pull/3795

I slightly prefer the explicit version, but I'm okay with the implicit version.



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