Disallow pending interrupts to be checked during FiberScheduler#unblock

[luke-gruber]

Ractors can send signals at any time, so the previous debug assertion can fail if a Ractor sends a signal.

require 'async/scheduler'

scheduler = Async::Scheduler.new
Fiber.set_scheduler(scheduler)

Signal.trap(:INT) do
end

q =  Thread::Queue.new

Thread.new do
  loop do
    Ractor.new do
      Process.kill(:INT, $$)
    end.value
  end
end

Fiber.schedule do
  Fiber.schedule do
    1.upto(1000000) do |i|
      sleep 0.01
      q.pop
      q.push(1)
      puts "1 iter push/pop"
    end
  end
  Fiber.schedule do
    1.upto(1000000) do |i|
      sleep 0.01
      q.push(i)
      q.pop
      puts "1 iter push/pop#2"
    end
  end
end

[samuel-williams-shopify]

I worked on a PR (ruby#14588), but I think your implementation is probably better. I'm going to try your implementation (will apply a commit on top of my PR to track progress).

[samuel-williams-shopify]

My PR is updated with this fix, I've tested and confirmed the fix according to the reproduction, and have created an upstream bug report. https://bugs.ruby-lang.org/issues/21610

[ioquatix]

Merged upstream.

[luke-gruber]

Awesome, thanks! ❤️