[issue9945] Improper locking in logging

[Armin Ronacher]

New submission from Armin Ronacher <armin.ronacher at active-4.com>:

I found a a useless lock acquiring in the 27 maintenance branch in logging and a missing one as well:

Logger.removeHandler() locks around a handler lock, however the code executed in this lock is not depending on anything of that lock.  However there is a race condition when two pieces of code try to remove the same handler at the same time because between the if and the remove() no locking takes place.

I would recommend this instead (and also add locking to the addHandler):

    def addHandler(self, hdlr):
        """
        Add the specified handler to this logger.
        """
        _acquireLock()
        try:
            if hdlr not in self.handlers:
                self.handlers.append(hdlr)
        finally:
            _releaseLock()

    def removeHandler(self, hdlr):
        """
        Remove the specified handler from this logger.
        """
        _acquireLock()
        try:
            if hdlr in self.handlers:
                self.handlers.remove(hdlr)
        finally:
            _releaseLock()

I suppose in 3.x there might be something similar.

----------
assignee: vinay.sajip
components: Library (Lib)
messages: 117364
nosy: aronacher, vinay.sajip
priority: normal
severity: normal
status: open
title: Improper locking in logging
type: behavior
versions: Python 2.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue9945>
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