def test_recently_written_and_lock_not_acquired( global_watch, global_compare_and_swap ): global_watch.return_value = _future_result(True) global_compare_and_swap.return_value = _future_result(False) lock = _cache.global_lock_for_read(b"key", _cache._LOCKED_FOR_WRITE).result() assert lock is None
def test_lock_acquired(global_set_if_not_exists): global_set_if_not_exists.return_value = _future_result(True) lock = _cache.global_lock_for_read(b"key", None).result() assert lock.startswith(_cache._LOCKED_FOR_READ)
def test_lock_not_acquired(global_set_if_not_exists): global_set_if_not_exists.return_value = _future_result(False) lock = _cache.global_lock_for_read(b"key", None).result() assert lock is None
def lookup(key, options): """Look up a Datastore entity. Gets an entity from Datastore, asynchronously. Checks the global cache, first, if appropriate. Uses batching. Args: key (~datastore.Key): The key for the entity to retrieve. options (_options.ReadOptions): The options for the request. For example, ``{"read_consistency": EVENTUAL}``. Returns: :class:`~tasklets.Future`: If not an exception, future's result will be either an entity protocol buffer or _NOT_FOUND. """ context = context_module.get_context() use_datastore = context._use_datastore(key, options) if use_datastore and options.transaction: use_global_cache = False else: use_global_cache = context._use_global_cache(key, options) if not (use_global_cache or use_datastore): raise TypeError("use_global_cache and use_datastore can't both be False") entity_pb = _NOT_FOUND key_locked = False if use_global_cache: cache_key = _cache.global_cache_key(key) result = yield _cache.global_get(cache_key) key_locked = _cache.is_locked_value(result) if not key_locked: if result: entity_pb = entity_pb2.Entity() entity_pb.MergeFromString(result) elif use_datastore: lock = yield _cache.global_lock_for_read(cache_key, result) if lock: yield _cache.global_watch(cache_key, lock) else: # Another thread locked or wrote to this key after the call to # _cache.global_get above. Behave as though the key was locked by # another thread and don't attempt to write our value below key_locked = True if entity_pb is _NOT_FOUND and use_datastore: batch = _batch.get_batch(_LookupBatch, options) entity_pb = yield batch.add(key) # Do not cache misses if use_global_cache and not key_locked: if entity_pb is not _NOT_FOUND: expires = context._global_cache_timeout(key, options) serialized = entity_pb.SerializeToString() yield _cache.global_compare_and_swap( cache_key, serialized, expires=expires ) else: yield _cache.global_unwatch(cache_key) raise tasklets.Return(entity_pb)