Question

Why does this code work (I see the output 1 2 3):

for i in 1..3
    Thread.new{
        puts i
    }
end

However, the following code does not produce the same output (I do not see the output 1 2 3)?

for i in 1..3
    Thread.new{
        sleep(5)
        puts i
    }
end

Answer 1

When you hit the end of the script, Ruby exits. If you add sleep 10 after the final loop, you can see the output show up. (Albeit, as 3 each time, because the binding to i reflects the value at the end of processing, and the sleep causes a thread switch back to the loop.)

You might want something like:

threads = []
for i in 1..3
  threads << Thread.new {
    sleep 5
    puts i
  }
end
threads.map {|t| t.join }

That will wait for all the threads to terminate before exiting.