Python Really Thread Safe Dictionary (“RuntimeErro

问题:

I've accidentialy got a threaded application due to the use of web.py and pyinotify packages :)

The application keeps sorta state in JSON files, which it may change and which can be changed by anyone else. Changed JSON is reloaded back into a dict by inotify watcher thread.

The application runs a dozen of threads in quite simple conditions.

Well, finally I observe

RuntimeError: dictionary changed size during iteration.

I realized, I need a lock around each and every dictionary operation. On this (these actually) dictionary, I mean.

I tried to work it around in quite different ways (yes, digging stackoverflow mostly).

I faced deadlocks in case of non-reentrant locks (that looks obvious to me now).

I ended up with this approach:

DictLock = threading.RLock # use reentrant locks here!

class ThreadSafeDict(dict):
    '''It must avoid things like
       RuntimeError: dictionary changed size during iteration.

       Inspired by https://stackoverflow.com/questions/13456735
       and https://stackoverflow.com/questions/3278077
    '''

    def __init__(self, *av, **kw):
        self._lock = kw.pop('_lock') if '_lock' in kw else DictLock()
        super(ThreadSafeDict, self).__init__(*av, **kw)
        self._thread = None

    # do NO LOCKS here!

    def replace(self, dictionary):
        super(ThreadSafeDict, self).clear()
        super(ThreadSafeDict, self).update(dictionary)
        return self

    def load_json(self, filename):
        with open(filename) as fp:
            super(ThreadSafeDict, self).clear()
            super(ThreadSafeDict, self).update(json.load(fp))
        return self

    def save_json(self, filename, indent=2):
        with open(filename, 'w') as fp:
            json.dump(self, fp, indent=indent)
        return self

    # all locking is being performed below

    def __getattribute__(self, name):
        if name == '_lock':
            return super(ThreadSafeDict, self).__getattribute__(name)
        with self._lock:
            self._thread = threading.current_thread()
            item = super(ThreadSafeDict, self).__getattribute__(name)
            if not callable(item):
                log.debug('[%r]=>%r', name, item)
                return item # return property value as is
            def wrapper(*a, **k):
                with self._lock:
                    return item(*a, **k)
            log.debug('%r()=>{%r}', name, item.__name__)
        return wrapper # return locked calls for methods

#end class ThreadSafeDict

The problem looks gone...

The questions is: Did I do it right? (I hope, this doesn't violate the "We prefer questions that can be answered, not just discussed." rule: it can be answered, anyway).