I am using tailable cursors to read a capped collection as it get written:

    while True:
        try:
            with collection.find(tailable=True, await_data=True, timeout=True, sort=[("$natural", ASCENDING)]) as cursor:
                while cursor.alive:
                    for doc in cursor:
                        callback(doc)
                            
            gevent.sleep(1)
        except:
            trace_exception()

It works fine most of the time, however I noticed a problem happening randomly. Sometimes, if I shut down the MongoDB server, the cursor doesn't detect the disconnection, and stays in an endless loop without raising any error.

I think the problem may be in cursor.py. In refresh, self._id appears to be 0, so the "elif self._id" statement is skipped, and the cursor doesn't try to get more data from the server, so no error is ever raised.