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)