Zenpy Cachetools implementation is not ThreadSafe and doesn't have a lock

[Vygo]

We've been getting KeyError from Cachetool and after internal investigation we found out that it is coming from with the zenpy usage of cachetools

Zenpy uses cachetools internally and doesn’t have a lock

In zenpy/lib/cache there exists class ZenpyCache(object): which has a lock around the purge function but nothing else.

def purge(self):
    """ Purge the cache of all items. """
    with self.purge_lock:
        self.cache.clear()

The issue is that other functions on the class such as

def __delitem__(self, key):
    del self.cache[key]

have no lock, and if multiple deletes happen at the same time in different threads, it causes a key error. This is the sequence of events within cachetools

Thread 1: Check for things ready for delete -> Finds key ABC123
Thread 2: Check for things ready for delete -> Finds key ABC123
Thread 1: Deletes ABC123 -> Success
Thread 2: Deletes ABC123 -> KeyError!

[cryptomail]

Interesting.....I don't know the state of the project as it relates to thread safety but this potentially could be shored up. Would you like to:

1. create a PR against this to synchronize access/deletes?
2. create tests that prove you've defeated the race conditions?

[cryptomail]

Closing due to inactivity. While I think it's a good idea, no one has stepped up to take this issue on.