Semaphore using EventMachine gratifications.

semaphore.rb

  # Execute an IMAP command from the frontend
  # API on a specific user's ImapConnection.
  #
  # @param command [symbol] the command to execute.
  # @param params [Hash] the parameters for the command.
  def execute_imap_command(command, params)
    log_info("executing #{command} for #{email}")

    # we should re-select the mailbox
    # once per command executed.
    @imap_connection.mailbox = nil
    previous_command = @previous_command

    # Use EM gratifications to create a mutex on imap commands.
    if previous_command && previous_command.instance_variable_get(:@deferred_status) == :unknown
      @previous_command = previous_command.
        bind! do
          @imap_connection.send(command, params)
        end
    else
      @previous_command = @imap_connection.send(command, params)
    end
end