Demonstration of a race condition in RabbitMQ Bunny's Channel#wait_for_confirms (https://github.com/ruby-amqp/bunny/issues/424)

demonstrate-bunny-wait_for_confirms-race-condition.rb

require 'thread'
require 'bunny'

operations_log = []
operations_log_mutex = Mutex.new

c = Bunny::Session.new
c.start

ch = c.create_channel

ch.confirm_select(proc { |tag, _, is_nack|
  operation = "#{'n' if is_nack}ack of #{tag}"
  operations_log_mutex.synchronize { operations_log << operation }
})

x = ch.default_exchange
q = ch.queue('', exclusive: true)

x.publish('msg', routing_key: q.name)
sleep 0.5 # Wait for the confirmation to be processed

# Artificially simulate a slower Ack
def (x.channel).handle_ack_or_nack(delivery_tag_before_offset, multiple, nack)
  sleep 1
  super
end

x.publish('msg', routing_key: q.name)
sleep 0.5
x.publish('msg', routing_key: q.name)

if x.wait_for_confirms
  operation = 'all confirmed'
  operations_log_mutex.synchronize { operations_log << operation }
end

# Wait a bit for the last confirm to arrive
sleep 2

# Check the operations log
#
# Expected: ["ack of 1", "ack of 2", "ack of 3", "all confirmed"]
# Actual:   ["ack of 1", "all confirmed", "ack of 2", "ack of 3"]
p operations_log