CODEWITHSUNDEEP
google-app-engineapp-engine-ndb
Pascal Bourque
Pascal Bourque

Reputation: 5309

Is it safe to yield a ndb.Future more than once?

Is it safe to do this?

@ndb.tasklet
def foo():
    # Note that I do not yield right here
    future = some_key.get_async()

    # Perform some other code

    if some_condition:
        # I need the get_async result here
        entity = yield future

    # I also need the get_async result here.
    # If some_condition was true, I would be yielding this future
    # for the second time. Is this ok?
    entity = yield future

Please don't tell me that I could just yield at the top of the function and use entity in the rest of the code. My actual function is a little more elaborate than this, and I have a few conditional codepaths that may need to use entity and I want to yield at the latest moment possible to be able to perform my other code while the entity is being fetched in the background.

Upvotes: 2

Views: 168

Answers (1)

tesdal
tesdal

Reputation: 2459

Yes, it's safe!

If you check the Future class in ndb, it will set result when done, and multiple yields or get_result will check if it's done and return the stored result.

google/appengine/ext/ndb/tasklets.py, line 324 in SDK 1.7.4

Upvotes: 2

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