def update(self, doc, process=None):
        if process is None:
            pk = 'id'
            id = doc.id
            doc.synced = False
            set = doc
        elif process == UPDATE_PROCESS:
            if self.db.docs.find({'sid': doc.sid}).count() == 0:
                return self.insert(doc, synced=True)
            pk = 'sid'
            id = doc.sid
            doc.synced = not doc.merged() # must be commited if was merged
            doc.merged(False)
            set = {'tid': doc.tid, 'data': doc.data, 'user': doc.user,
                   'public': doc.public, 'synced': doc.synced}
        elif process == COMMIT_PROCESS:
            pk = 'id'
            id = doc.id
            doc.synced = True
            set = {'sid': doc.sid, 'tid': doc.tid, 'synced': doc.synced}
        else:
            raise DatabaseException('Incorrect update process')

        try:
            rs = self.db.docs.update({pk: id}, {'$set': set}, safe=True)
            assert rs['n'] == 1
        except Exception as e:
            raise DatabaseException(e)
        return doc
def reset_signal_handler(cls, signal_handler):
        """Class state:

        - Overwrites `cls._signal_handler`.
        OS state:
        - Overwrites signal handlers for SIGINT, SIGQUIT, and SIGTERM.

        NB: This method calls signal.signal(), which will crash if not called from the main thread!

        :returns: The :class:`SignalHandler` that was previously registered, or None if this is
                  the first time this method was called.
        """
        assert isinstance(signal_handler, SignalHandler)
        # NB: Modify process-global state!
        for signum, handler in signal_handler.signal_handler_mapping.items():
            signal.signal(signum, handler)
            # Retry any system calls interrupted by any of the signals we just installed handlers for
            # (instead of having them raise EINTR). siginterrupt(3) says this is the default behavior on
            # Linux and OSX.
            signal.siginterrupt(signum, False)

        previous_signal_handler = cls._signal_handler
        # NB: Mutate the class variables!
        cls._signal_handler = signal_handler
        return previous_signal_handler