Ruby threads and variable

Question

Why the result is not from 1 to 10, but 10s only?

require \'thread\'

def run(i)
  puts i
end

while true
  for i in 0..10
    Thread.new{ run(i)}
  end
  sl         


        

Answer 1

The block that is passed to Thread.new may actually begin at some point in the future, and by that time the value of i may have changed. In your case, they all have incremented up to 10 prior to when all the threads actually run.

To fix this, use the form of Thread.new that accepts a parameter, in addition to the block:

require 'thread'

def run(i)
  puts i
end

while true
  for i in 0..10
    Thread.new(i) { |j| run(j) }
  end
  sleep(100)
end

This sets the block variable j to the value of i at the time new was called.