fiber-backtrace.rb

require 'thread'

input = Queue.new
output = Queue.new

thread = Thread.new {
  one = Fiber.new {
    loop {
      p(running: :one)
      output << :one
      sleep 2
      Fiber.yield
    }
  }.resume

  two = Fiber.new {
    loop {
      p(running: :two)
      output << :two
      sleep 2
      Fiber.yield
    }
  }.resume

  while fiber = input.pop
    {one: one, two: two}.resume
  end
}

input << :one
output.pop
puts "backtrace running one"
puts thread.backtrace
input << :two
output.pop
puts "backtrace running two"
puts thread.backtrace