Python中logging在多进程环境下打印日志

因为涉及到进程间互斥与通信问题，因此默认情况下Python中的logging无法在多进程环境下打印日志。但是查询了官方文档可以发现，推荐了一种利用logging.SocketHandler的方案来实现多进程日志打印。

其原理很简单，概括一句话就是说：多个进程将各自环境下的日志通过Socket发送给一个专门打印日志的进程，这样就可以防止多进程打印的冲突与混乱情况。

本文主要记录下SocketHandler真实的用法情况：

1 时序图

简单说明下逻辑：主进程（MainProcess）启动一个专门打印日志的进程（LogReceiverProcess），并且将自己（主进程）环境下的日志都“重定向”给LogReceiverProcess。同理，在后续逻辑中启动的所有工作子进程（WorkerProcess）都做一样的操作，把自己环境下的日志都“重定向”给日志进程去打印。

2 实现代码

2.1 日志进程

　　日志进程的代码核心在于要建立一个TCP Server来接收并处理Log record，代码如下：

 import os
 import logging
 import logging.handlers
 import traceback
 import cPickle
 import struct
 import SocketServer
 from multiprocessing import Process

 class LogRecordStreamHandler(SocketServer.StreamRequestHandler):
     def handle(self):
         while True:
             try:
                 chunk = self.connection.recv(4)
                 if len(chunk) < 4:
                     break
                 slen = struct.unpack(">L", chunk)[0]
                 chunk = self.connection.recv(slen)
                 while len(chunk) < slen:
                     chunk = chunk + self.connection.recv(slen - len(chunk))
                 obj = self.unpickle(chunk)
                 record = logging.makeLogRecord(obj)
                 self.handle_log_record(record)

             except:
                 break

     @classmethod
     def unpickle(cls, data):
         return cPickle.loads(data)

     def handle_log_record(self, record):
         if self.server.logname is not None:
             name = self.server.logname
         else:
             name = record.name
         logger = logging.getLogger(name)
         logger.handle(record)

 class LogRecordSocketReceiver(SocketServer.ThreadingTCPServer):
     allow_reuse_address = 1

     def __init__(self, host='localhost', port=logging.handlers.DEFAULT_TCP_LOGGING_PORT, handler=LogRecordStreamHandler):
         SocketServer.ThreadingTCPServer.__init__(self, (host, port), handler)
         self.abort = 0
         self.timeout = 1
         self.logname = None

     def serve_until_stopped(self):
         import select
         abort = 0
         while not abort:
             rd, wr, ex = select.select([self.socket.fileno()], [], [], self.timeout)
             if rd:
                 self.handle_request()
             abort = self.abort

 def _log_listener_process(log_format, log_time_format, log_file):
     log_file = os.path.realpath(log_file)
     logging.basicConfig(level=logging.DEBUG, format=log_format, datefmt=log_time_format, filename=log_file, filemode='a+')

     # Console log
     console = logging.StreamHandler()
     console.setLevel(logging.INFO)
     console.setFormatter(logging.Formatter(fmt=log_format, datefmt=log_time_format))
     logging.getLogger().addHandler(console)

     tcp_server = LogRecordSocketReceiver()

     logging.debug('Log listener process started ...')
     tcp_server.serve_until_stopped()

　　关键点：

（1）TCPServer的构建逻辑，拆包还原Log记录；

（2）在日志进程中设定好logging记录级别和打印方式，这里除了指定文件存储还添加了Console打印。

2.2 其他进程

　　除了日志进程之外的进程，设置logging都“重定向”给日志进程，并且要关闭当前进程的日志在Console打印（默认会显示Warning级别及以上的日志到Console），否则Console上日志展示会有重复凌乱的感觉。

 class LogHelper:
     # 默认日志存储路径（相对于当前文件路径）
     default_log_path = os.path.join(os.path.dirname(os.path.realpath(__file__)), '..', 'logs')

     # 记录当前实际的日志所在目录
     current_log_path = ''

     # 记录当前实际的日志完整路径
     current_log_file = ''

     # 日志文件内容格式
     log_format = '[%(asctime)s.%(msecs)03d][%(processName)s][%(levelname)s][%(filename)s:%(lineno)d] %(message)s'

     # 日志中时间格式
     log_time_format = '%Y%m%d %H:%M:%S'

     # 日志进程
     log_process = None

     def __init__(self):
         pass

     @staticmethod
     def print_console_log(level, message):
         print '--------------------------------------------------'
         if level == logging.WARN:
             level_str = '[WARN]'
         elif level == logging.ERROR:
             level_str = '[ERROR]'
         elif level == logging.FATAL:
             level_str = '[FATAL]'
         else:
             level_str = '[INFO]'
         print '\t%s %s' % (level_str, message)
         print '--------------------------------------------------'

     @staticmethod
     def init(clear_logs=True, log_path=''):
         #
         console = logging.StreamHandler()
         console.setLevel(logging.FATAL)
         logging.getLogger().addHandler(console)

         try:
             # 如果外部没有指定日志存储路径则默认在common同级路径存储
             if log_path == '':
                 log_path = LogHelper.default_log_path
                 if not os.path.exists(log_path):
                     os.makedirs(log_path)
             LogHelper.current_log_path = log_path

             # 清理旧的日志并初始化当前日志路径
             if clear_logs:
                 LogHelper.clear_old_log_files()
             LogHelper.current_log_file = LogHelper._get_latest_log_file()

             socket_handler = logging.handlers.SocketHandler('localhost', logging.handlers.DEFAULT_TCP_LOGGING_PORT)
             logging.getLogger().setLevel(logging.DEBUG)
             logging.getLogger().addHandler(socket_handler)

             #
             LogHelper.start()

         except Exception, ex:
             LogHelper.print_console_log(logging.FATAL, 'init() exception: %s' % str(ex))
             traceback.print_exc()

     @staticmethod
     def start():
         if LogHelper.log_process is None:
             LogHelper.log_process = Process(target=_log_listener_process, name='LogRecorder', args=(LogHelper.log_format, LogHelper.log_time_format, LogHelper.current_log_file))
             LogHelper.log_process.start()
         else:
             pass

     @staticmethod
     def stop():
         if LogHelper.log_process is None:
             pass
         else:
             LogHelper.log_process.terminate()
             LogHelper.log_process.join()

     @staticmethod
     def _get_latest_log_file():
         latest_log_file = ''
         try:
             if os.path.exists(LogHelper.current_log_path):
                 for maindir, subdir, file_name_list in os.walk(LogHelper.current_log_path):
                     for file_name in file_name_list:
                         apath = os.path.join(maindir, file_name)
                         if apath > latest_log_file:
                             latest_log_file = apath

             if latest_log_file == '':
                 latest_log_file = LogHelper.current_log_path + os.sep + 'system_'
                 latest_log_file += time.strftime("%Y%m%d_%H%M%S", time.localtime(time.time())) + '.log'

         except Exception, ex:
             logging.error('EXCEPTION: %s' % str(ex))
             traceback.print_exc()

         finally:
             return latest_log_file

     @staticmethod
     def get_log_file():
         return LogHelper.current_log_file

     @staticmethod
     def clear_old_log_files():
         if not os.path.exists(LogHelper.current_log_path):
             logging.warning('clear_old_log_files() Not exist: %s' % LogHelper.current_log_path)
             return

         try:
             for maindir, subdir, file_name_list in os.walk(LogHelper.current_log_path):
                 for file_name in file_name_list:
                     apath = os.path.join(maindir, file_name)
                     if apath != LogHelper.current_log_file:
                         logging.info('DEL -> %s' % str(apath))
                         os.remove(apath)
                     else:
                         with open(LogHelper.current_log_file, 'w') as f:
                             f.write('')

             logging.debug('Clear log done.')

         except Exception, ex:
             logging.error('EXCEPTION: %s' % str(ex))
             traceback.print_exc()