Class: Que::Listener

Inherits:
Object
  • Object
show all
Defined in:
lib/que/listener.rb

Constant Summary collapse

MESSAGE_FORMATS = 
{}

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(connection:, channel: nil) ⇒ Listener

Returns a new instance of Listener.



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# File 'lib/que/listener.rb', line 9

def initialize(connection:, channel: nil)
  @connection = connection
  @channel    = channel || "que_listener_#{connection.backend_pid}"

  Que.internal_log :listener_instantiate, self do
    {
      backend_pid: connection.backend_pid,
    }
  end
end

Instance Attribute Details

#channel ⇒ Object (readonly)

Returns the value of attribute channel.



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# File 'lib/que/listener.rb', line 7

def channel
  @channel
end

#connection ⇒ Object (readonly)

Returns the value of attribute connection.



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# File 'lib/que/listener.rb', line 7

def connection
  @connection
end

Instance Method Details

#listen ⇒ Object 



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# File 'lib/que/listener.rb', line 20

def listen
  connection.execute "LISTEN #{channel}"
end

#unlisten ⇒ Object 



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# File 'lib/que/listener.rb', line 129

def unlisten
  # Be sure to drain all notifications so that any code that uses this
  # connection later doesn't receive any nasty surprises.
  connection.execute "UNLISTEN *"
  connection.drain_notifications

  Que.internal_log :listener_unlisten, self do
    {
      backend_pid: connection.backend_pid,
      channel:     channel,
    }
  end
end

#wait_for_grouped_messages(timeout) ⇒ Object 



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# File 'lib/que/listener.rb', line 24

def wait_for_grouped_messages(timeout)
  messages = wait_for_messages(timeout)

  output = {}

  messages.each do |message|
    message_type = message.delete(:message_type)

    (output[message_type.to_sym] ||= []) << message.freeze
  end

  output
end

#wait_for_messages(timeout) ⇒ Object 



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# File 'lib/que/listener.rb', line 38

def wait_for_messages(timeout)
  # Make sure we never pass nil to this method, so we don't hang the thread.
  Que.assert(Numeric, timeout)

  Que.internal_log :listener_waiting, self do
    {
      backend_pid: connection.backend_pid,
      channel:     channel,
      timeout:     timeout,
    }
  end

  accumulated_messages = []

  # Notifications often come in batches (especially when a transaction that
  # inserted many jobs commits), so we want to loop and pick up all the
  # received notifications before continuing.
  loop do
    notification_received =
      connection.wait_for_notify(timeout) do |channel, pid, payload|
        # We've received a notification, so zero out the timeout before we
        # loop again to check for another message. This ensures that we
        # don't wait an additional `timeout` seconds after processing the
        # final message before this method returns.
        timeout = 0

        Que.internal_log(:listener_received_notification, self) do
          {
            channel:     channel,
            backend_pid: connection.backend_pid,
            source_pid:  pid,
            payload:     payload,
          }
        end

        # Be very defensive about the message we receive - it may not be
        # valid JSON or have the structure we expect.
        next unless message = parse_payload(payload)

        case message
        when Array then accumulated_messages.concat(message)
        when Hash  then accumulated_messages << message
        else raise Error, "Unexpected parse_payload output: #{message.class}"
        end
      end

    break unless notification_received
  end

  return accumulated_messages if accumulated_messages.empty?

  Que.internal_log(:listener_received_messages, self) do
    {
      backend_pid: connection.backend_pid,
      channel:     channel,
      messages:    accumulated_messages,
    }
  end

  accumulated_messages.keep_if do |message|
    next unless message.is_a?(Hash)
    next unless type = message[:message_type]
    next unless type.is_a?(String)
    next unless format = MESSAGE_FORMATS[type.to_sym]

    if message_matches_format?(message, format)
      true
    else
      error_message = [
        "Message of type '#{type}' doesn't match format!",
        # Massage message and format a bit to make these errors more readable.
        "Message: #{Hash[message.reject{|k,v| k == :message_type}.sort_by{|k,v| k}].inspect}",
        "Format: #{Hash[format.sort_by{|k,v| k}].inspect}",
      ].join("\n")

      Que.notify_error_async(Error.new(error_message))
      false
    end
  end

  Que.internal_log(:listener_filtered_messages, self) do
    {
      backend_pid: connection.backend_pid,
      channel:     channel,
      messages:    accumulated_messages,
    }
  end

  accumulated_messages
end