Question

I have a thread doing things in background and I want to suspend it whenever my program has a real thing to do. Once that is finished I want the background thread to continue. E.g.

ta = Thread.new { loop { print 'a'; sleep 0.2 } }

sleep 0.5

# put ta to sleep
5.times { print 'b'; sleep 0.2 }
# let ta resume

sleep 0.8
puts

The output should be something like aaabbbbbaaaaa. Currently it is aaabababababaaaaa.

Although a thread can stop itself through Thread.stop, I found no method to stop a thread from “outside”. Is there a simple solution?

Answer 1

What you need is a Mutex:

$my_mutex = Mutex.new

t1 = Thread.new do
  loop do
    $my_mutex.synchronize do
      print 'a'
    end
    sleep 0.2
  end
end

sleep 0.5

$my_mutex.synchronize do
  5.times do
    print 'b'
    sleep 0.2
  end
end

sleep 0.8

puts
sleep

Output:

aaabbbbbaaaaa
aaaaaaaaaaaaaaaaa...