single_task.py

def single_instance_task(function=None, timeout=None):
    """Enforce only one celery task at a time."""

    def _dec(run_func):
        """Decorator."""

        @wraps(run_func)
        def _caller(*args, **kwargs):
            """Caller."""
            ret_value = None
            have_lock = False

            s = json.dumps({'a': args, 'kw': kwargs})
            key = "lock.%s.%s.%s" % (run_func.__module__, run_func.__name__, md5(s).hexdigest())
            lock = cache.lock(key, timeout=timeout)
            try:
                have_lock = lock.acquire(blocking=False)
                if have_lock:
                    ret_value = run_func(*args, **kwargs)
            finally:
                if have_lock:
                    lock.release()

            return ret_value

        return _caller

    return _dec(function) if function is not None else _dec


@periodic_task(run_every=10, time_limit=86400)
@single_instance_task(timeout=86400)
def run_stuff():
    # Might take awhile!
    pass