CODEWITHSUNDEEP
ruby
daremkd
daremkd

Reputation: 8424

Why is this Ruby threading code outputting 2?

Thread.abort_on_exception = true
threads = 4.times.map do |number|
  Thread.new(number) do |i|
    raise "Boom!" if i == 1
    print "#{i}\n"
  end
end

puts "Waiting"
threads.each {|t| t.join }
puts "Done"

produces 0, 2 and then the error. I don't understand why it outputs 2 every time when it makes sense to output only 0 and then exit?

Upvotes: 0

Views: 50

Answers (1)

Niels B.
Niels B.

Reputation: 6310

It's a scheduling issue. The threads don't truly run in parallel. Instead the Ruby interpreter continuously switches between the executing threads.

In this case, thread 1 raises an exception which must be handled. This presumably takes enough time to allow thread 2 to execute.

Try putting in a sleep 0.1 between the raise and the print line, that should result in no output at all.

Upvotes: 2

Related Questions