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log

Desc

处理tronado框架中的日志记录。

Notices

  1. tornado.log模块配置的是Python的logging模块中的root logger。tornado.log模块的log相关参数设置都是针对root logger。Tornado框架中的各个自定义的logger最后的日志记录请求都会被委托给root logger，包括日志记录级别(log level)和相应的日志处理器（handler)

  2. Python中logging模块的原理。

  • Python中的logging模块中的logger是树形结构，根节点是root logger，子节点是自定义的logger。每个logger的parent属性指示父logger。root logger的parent属性是None。

  • 默认，root logger在导入logging模块的时候就会被创建，root logger的日志级别是WARNING。

  • 当一个logger被创建的时候，日志级别默认是NOTSET，这会导致：如果接收请求的logger是root logger则所有级别的日志信息都被记录；否则会把相应的日志记录请求委托给父logger。

    • 将日志记录请求委托给父logger的意思：
      • 如果接收请求的logger日志级别是NOTSET,接收请求的logger的所有祖先logger会被逆序遍历直到一个祖先logger的日志级别不是NOTSET或者遍历到root logger。
      • 如果一个日志级别不是NOTSET的祖先logger被遍历到，则这个祖先logger的日志级别会被作为当前logger的有效日志级别，并根据这个有效日志级别来确定是否能处理日志记录请求。
      • 如果最后root logger被遍历到，并且root logger的日志级别是NOTSET，则所有的日志请求都会被满足；否则，将root logger的日志级别作为接收请求的logger的有效日志级别。
      • logging.Logger.getEffectiveLevel
      def getEffectiveLevel(self):
  """
  Get the effective level for this logger.

  Loop through this logger and its parents in the logger hierarchy,
  looking for a non-zero logging level. Return the first one found.
  """
  logger = self
  while logger:
      if logger.level:
          return logger.level
      logger = logger.parent
  return NOTSET

  • 处理器(handler)

    • 在处理日志记录请求的时候，会调用logging.Logger.Callhandlers。该函数的主要功能是在接收请求的logger和祖先logger中进行遍历，直到一个祖先logger的propagate属性变成False或者到达root logger（root logger的parent属性为None)。
    def callHandlers(self, record):
    """
    Pass a record to all relevant handlers.

    Loop through all handlers for this logger and its parents in the
    logger hierarchy. If no handler was found, output a one-off error
    message to sys.stderr. Stop searching up the hierarchy whenever a
    logger with the "propagate" attribute set to zero is found - that
    will be the last logger whose handlers are called.
    """
    c = self
    found = 0
    while c:
        for hdlr in c.handlers:
            found = found + 1
            if record.levelno >= hdlr.level:
                hdlr.handle(record)
        if not c.propagate:
            c = None    #break out
        else:
            c = c.parent
    if (found == 0) and raiseExceptions and not self.manager.emittedNoHandlerWarning:
        sys.stderr.write("No handlers could be found for logger"
                         " \"%s\"\n" % self.name)
        self.manager.emittedNoHandlerWarning = 1
  1. root logger
  • 通过tornado.log.enable_pretty_logging进行配置，包括日志级别(log level)和处理(handler)。
def enable_pretty_logging(options=None, logger=None):
  """Turns on formatted logging output as configured.

  This is called automatically by `tornado.options.parse_command_line`
  and `tornado.options.parse_config_file`.
  """
  if options is None:
      from tornado.options import options
  if options.logging is None or options.logging.lower() == 'none':
      return
  if logger is None:
      logger = logging.getLogger()
  logger.setLevel(getattr(logging, options.logging.upper()))
  if options.log_file_prefix:
      rotate_mode = options.log_rotate_mode
      if rotate_mode == 'size':
          channel = logging.handlers.RotatingFileHandler(
              filename=options.log_file_prefix,
              maxBytes=options.log_file_max_size,
              backupCount=options.log_file_num_backups)
      elif rotate_mode == 'time':
          channel = logging.handlers.TimedRotatingFileHandler(
              filename=options.log_file_prefix,
              when=options.log_rotate_when,
              interval=options.log_rotate_interval,
              backupCount=options.log_file_num_backups)
      else:
          error_message = 'The value of log_rotate_mode option should be ' +\
                          '"size" or "time", not "%s".' % rotate_mode
          raise ValueError(error_message)
      channel.setFormatter(LogFormatter(color=False))
      logger.addHandler(channel)

  if (options.log_to_stderr or
          (options.log_to_stderr is None and not logger.handlers)):
      # Set up color if we are in a tty and curses is installed
      channel = logging.StreamHandler()
      channel.setFormatter(LogFormatter())
      logger.addHandler(channel)
  1. access_log/gen_log/app_log
  • 在tornado.log模块级别进行定义 
    # Logger objects for internal tornado use
access_log = logging.getLogger("tornado.access")
app_log = logging.getLogger("tornado.application")
gen_log = logging.getLogger("tornado.general")
  • 根据1和2的解析，不难理解access_log/gen_log/app_log都没有定义日志级别和注册处理器，所以它们默认会根据2中的解释使用root logger的日志级别和处理器