I am working in multi-threading in Ruby. The code snippet is:

  threads_array = Array.new(num_of_threads)  
  1.upto(num_of_threads) do |i|  

    Thread.abort_on_exception = true
      threads_array[i-1] =  Thread.new {
        catch(:exit) do
          print "s #{i}"
          user_id = nil
          loop do
            user_id = user_ids.pop()
            if user_id == nil
              print "a #{i}"
              Thread.stop()
            end
            dosomething(user_id)
          end
        end
      }
    end
    #puts "after thread"
    threads_array.each {|thread| thread.join}

I am not using any mutex locks, but I get a deadlock. This is the output of the above code snippet:

s 2s 6s 8s 1s 11s 7s 10s 14s 16s 21s 24s 5s 26s 3s 19s 20s 23s 4s 28s 9s 12s 18s 22s 29s 30s 27s 13s 17s 15s 25a 4a 10a 3a 6a 21a 24a 16a 9a 18a 5a 28a 20a 2a 22a 11a 29a 8a 14a 23a 26a 1a 19a 7a 12fatal: deadlock detected

The above output tells me that the deadlock is after the user_ids array is null and happening with Thread's join and stop.

What actually is happening and what is the solution to this error?

ruby multithreading deadlock
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