From: "mame (Yusuke Endoh)" <noreply@...>
Date: 2021-09-16T14:20:59+00:00
Subject: [ruby-core:105306] [Ruby master Bug#17568] Thread.handle_interrupt is per-Thread but should probably be per-Fiber

Issue #17568 has been updated by mame (Yusuke Endoh).


ko1 (Koichi Sasada) wrote in #note-2:
> mame-san also proposed `Fiber.handle_interrupt` for fiber local handler to set fiber local setting.

No I didn't propose it actually. In today's dev meeting, we discussed that there are a case where per-Thread mask is needed (e.g., to take an element from an external enumerator), and a case where per-Fiber mask may be needed (I'm unsure about a concrete case though). I just said that, if so, it is theoretically possible to have both `Thread.handle_interrupt` for per-Thread mask and `Fiber.handle_interrupt` for per-Fiber mask (maybe per-Fiber mask takes precedence if any). But I have no idea whether per-Fiber mask is practically needed.

----------------------------------------
Bug #17568: Thread.handle_interrupt is per-Thread but should probably be per-Fiber
https://bugs.ruby-lang.org/issues/17568#change-93716

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
`Thread.handle_interrupt` and the pending interrupts is currently kept as state on the thread (`rb_thread_t`).
However, that seems potentially confusing when `Fiber`s are used.

For instance, this innocent-looking `Fiber` will forever disable interrupts in the main thread:
```ruby
main_thread = Thread.current

never_die = Fiber.new do
  Thread.handle_interrupt(RuntimeError => :never) do
    Fiber.yield
  end
end

begin
  Thread.new { main_thread.raise "interrupt1" }.join
rescue => e
  puts "raised: #{e}"
end

never_die.resume

Thread.new { main_thread.raise "interrupt2" }.join

Thread.new { main_thread.raise "interrupt3" }.join

p :after
```

Output is:
```
raised: interrupt1
:after
```

(I noticed these weird semantics when implementing `Thread.handle_interrupt` on TruffleRuby, and got a fairly subtle bug due to multiple `Fiber`s of the same `Thread` queuing the same interrupt multiple times in the `Thread`'s interrupt queue).



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