I have created a class ParallelTimedRotatingFileHandler mainly aimed at allowing multiple processes writing in parallel to a log file.
The problems with parallel processes solved by this class, are:
- The rollover moment when all processes are trying to copy or rename the same file at the same time, gives errors.
- The solution for this problem was exactly the naming convention you suggest. So, for a file name
Service that you supply in the handler, logging does not go to e.g. Service.log but today to Service.2014-08-18.log and tomorrow Service.2014-08-19.log.
- Another solution is to open the files in
a (append) mode instead of w to allow parallel writes.
- Deleting the backup files also needs to be done with caution as multiple parallel processes are deleting the same files at the same time.
- This implementation does not take into account leap seconds (which is not a problem for Unix). In other OS, it might still be 30/6/2008 23:59:60 at the rollover moment, so the date has not changed, so, we take the same file name as yesterday.
- I know that the standard Python recommendation is that the
logging module is not foreseen for parallel processes, and I should use SocketHandler, but at least in my environment, this works.
The code is just a slight variation of the code in the standard Python handlers.py module. Of course copyright to the copyright holders.
Here is the code:
import logging
import logging.handlers
import os
import time
import re
class ParallelTimedRotatingFileHandler(logging.handlers.TimedRotatingFileHandler):
def __init__(self, filename, when='h', interval=1, backupCount=0, encoding=None, delay=False, utc=False, postfix = ".log"):
self.origFileName = filename
self.when = when.upper()
self.interval = interval
self.backupCount = backupCount
self.utc = utc
self.postfix = postfix
if self.when == 'S':
self.interval = 1 # one second
self.suffix = "%Y-%m-%d_%H-%M-%S"
self.extMatch = r"^\d{4}-\d{2}-\d{2}_\d{2}-\d{2}-\d{2}$"
elif self.when == 'M':
self.interval = 60 # one minute
self.suffix = "%Y-%m-%d_%H-%M"
self.extMatch = r"^\d{4}-\d{2}-\d{2}_\d{2}-\d{2}$"
elif self.when == 'H':
self.interval = 60 * 60 # one hour
self.suffix = "%Y-%m-%d_%H"
self.extMatch = r"^\d{4}-\d{2}-\d{2}_\d{2}$"
elif self.when == 'D' or self.when == 'MIDNIGHT':
self.interval = 60 * 60 * 24 # one day
self.suffix = "%Y-%m-%d"
self.extMatch = r"^\d{4}-\d{2}-\d{2}$"
elif self.when.startswith('W'):
self.interval = 60 * 60 * 24 * 7 # one week
if len(self.when) != 2:
raise ValueError("You must specify a day for weekly rollover from 0 to 6 (0 is Monday): %s" % self.when)
if self.when[1] < '0' or self.when[1] > '6':
raise ValueError("Invalid day specified for weekly rollover: %s" % self.when)
self.dayOfWeek = int(self.when[1])
self.suffix = "%Y-%m-%d"
self.extMatch = r"^\d{4}-\d{2}-\d{2}$"
else:
raise ValueError("Invalid rollover interval specified: %s" % self.when)
currenttime = int(time.time())
logging.handlers.BaseRotatingHandler.__init__(self, self.calculateFileName(currenttime), 'a', encoding, delay)
self.extMatch = re.compile(self.extMatch)
self.interval = self.interval * interval # multiply by units requested
self.rolloverAt = self.computeRollover(currenttime)
def calculateFileName(self, currenttime):
if self.utc:
timeTuple = time.gmtime(currenttime)
else:
timeTuple = time.localtime(currenttime)
return self.origFileName + "." + time.strftime(self.suffix, timeTuple) + self.postfix
def getFilesToDelete(self, newFileName):
dirName, fName = os.path.split(self.origFileName)
dName, newFileName = os.path.split(newFileName)
fileNames = os.listdir(dirName)
result = []
prefix = fName + "."
postfix = self.postfix
prelen = len(prefix)
postlen = len(postfix)
for fileName in fileNames:
if fileName[:prelen] == prefix and fileName[-postlen:] == postfix and len(fileName)-postlen > prelen and fileName != newFileName:
suffix = fileName[prelen:len(fileName)-postlen]
if self.extMatch.match(suffix):
result.append(os.path.join(dirName, fileName))
result.sort()
if len(result) < self.backupCount:
result = []
else:
result = result[:len(result) - self.backupCount]
return result
def doRollover(self):
if self.stream:
self.stream.close()
self.stream = None
currentTime = self.rolloverAt
newFileName = self.calculateFileName(currentTime)
newBaseFileName = os.path.abspath(newFileName)
self.baseFilename = newBaseFileName
self.mode = 'a'
self.stream = self._open()
if self.backupCount > 0:
for s in self.getFilesToDelete(newFileName):
try:
os.remove(s)
except:
pass
newRolloverAt = self.computeRollover(currentTime)
while newRolloverAt <= currentTime:
newRolloverAt = newRolloverAt + self.interval
#If DST changes and midnight or weekly rollover, adjust for this.
if (self.when == 'MIDNIGHT' or self.when.startswith('W')) and not self.utc:
dstNow = time.localtime(currentTime)[-1]
dstAtRollover = time.localtime(newRolloverAt)[-1]
if dstNow != dstAtRollover:
if not dstNow: # DST kicks in before next rollover, so we need to deduct an hour
newRolloverAt = newRolloverAt - 3600
else: # DST bows out before next rollover, so we need to add an hour
newRolloverAt = newRolloverAt + 3600
self.rolloverAt = newRolloverAt
