We build a small project that watches multiple metrics until one of them finds something, I found ThreadsWait in the stdlib and it was easy to use it. Also added error re-raising so the threads do not die silently and cleanup.

require 'thwait'

def wait_for_first_block_to_complete(*blocks)
  threads = blocks.map do |block|
    Thread.new do
      block.call
    rescue StandardError => e
      e
    end
  end
  waiter = ThreadsWait.new(*threads)
  value = waiter.next_wait.value
  threads.each(&:kill)
  raise value if value.is_a?(StandardError)
  value
end

wait_for_first_block_to_complete(
  -> { sleep 5 }, -> { sleep 1 }, -> { sleep 2 }
) # will stop after 1 second