Using channels to communicate data safely

If sharing variables between fibers is not the proper way to communicate between fibers, then what is? The answer is channels. A channel is a way to communicate between fibers without needing to worry about race conditions, locks, semaphores, or other special structures. Let's take a look at the following example:

input_channel = Channel(Int32).new
output_channel = Channel(Int32).new
 
spawn do
  output_channel.send input_channel.receive * 2
end
 
input_channel.send 2
 
puts output_channel.receive

The preceding example creates two channels that contain the Int32 input and output values. Then it spawns a fiber that first receives a value from the input channel, doubles it, and sends it to the output channel. We then send the input channel an initial value of 2, and, finally, print the result we receive back from the output channel. As mentioned in the previous section, the fiber itself does not execute when we spawn it,...