safe-thread-yielding.rb

require 'thread'

def thing_yielder(&block)
  things = %i( a b c )
  yieldings = Queue.new

  threads = things.map do |thing|
    Thread.new do
      sleep rand(1..3) # Simulate work
      yieldings << thing
    end
  end

  threads.each(&:join)

  while thing = yieldings.shift(true) rescue nil
    yield thing
  end
end

puts "Main thread: #{Thread.current.object_id}"

thing_yielder do |thing|
  puts "Thread #{thing} yielded with thread #{Thread.current.object_id}"
end

# Main thread: 70313379624840
# Thread a yielded with thread 70313379624840
# Thread b yielded with thread 70313379624840
# Thread c yielded with thread 70313379624840

thread-yielding.rb

require 'thread'

def thing_yielder
  things = %i( a b c )
  
  threads = things.map do |thing|
    Thread.new do
      sleep rand(1..3)
      yield thing
    end
  end
  
  threads.each(&:join)
end

puts "Main thread: #{Thread.current.object_id}"

thing_yielder do |thing|
  puts "Thread #{thing} yielded with thread #{Thread.current.object_id}"
end

# Main thread: 70325593438120
# Thread a yielded with thread 70325610046980
# Thread b yielded with thread 70325610046460
# Thread c yielded with thread 70325610046180