def add(severity, progname, &block)
      return true if io.nil? || severity < level
      message = format_message(severity, progname, yield)
      MUTEX.synchronize { io.write(message) }
      true
    end
def add(severity, progname, &block)
      return true if io.nil? || severity < level
      message = format_message(severity, progname, yield)
      MUTEX.synchronize { io.write(message) }
      true
    end
Add a message to the logger with the given severity and progname.