Justin Bronder added the comment:
On 16/07/15 20:03 +0000, R. David Murray wrote:
>
> R. David Murray added the comment:
>
> Can you expand on the deadlock? Are you saying that the "extra" locking is
> causing the deadlock?
>
> ----------
> nosy: +r.david.murray, vinay.sajip
> versions: -Python 3.2, Python 3.3
>
> _______________________________________
> Python tracker <rep...@bugs.python.org>
> <http://bugs.python.org/issue24645>
> _______________________________________
Sure, here is the simplest example of the deadlock I could come up with. Using
__repr__() in the way presented is pretty stupid in this case but it does make
sense if you have objects which are backed by a database where communication is
handled in a separate thread.
What happens is this:
1. The main thread calls into the logger, handle() grabs the I/O lock.
2. String expansion of the Blah instance begins, this makes a request to the
second thread.
3. The second thread wants to log prior to responding, it gets stuck waiting
for
the I/O lock in handle()
import logging
import logging.handlers
import queue
import types
import threading
fmt = logging.Formatter('LOG: %(message)s')
stream = logging.StreamHandler()
stream.setFormatter(fmt)
log_queue = queue.Queue(-1)
queue_handler = logging.handlers.QueueHandler(log_queue)
queue_listener = logging.handlers.QueueListener(log_queue, stream)
queue_listener.start()
def handle(self, record):
rv = self.filter(record)
if rv:
self.emit(record)
return rv
# Uncomment to remove deadlock
#queue_handler.handle = types.MethodType(handle, queue_handler)
logger = logging.getLogger()
logger.addHandler(queue_handler)
logger.setLevel(logging.DEBUG)
class Blah(object):
def __init__(self):
self._in = queue.Queue()
self._out = queue.Queue()
def pub():
self._in.get(block=True)
logging.info('Got a request')
self._out.put('hi')
self._pub_thread = threading.Thread(target=pub)
self._pub_thread.start()
def __repr__(self):
self._in.put('gimme data')
return self._out.get()
def __del__(self):
self._pub_thread.join()
b = Blah()
logger.info('About to log')
logger.info('blah = %s', b)
queue_listener.stop()
----------
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue24645>
_______________________________________
_______________________________________________
Python-bugs-list mailing list
Unsubscribe:
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
