CODEWITHSUNDEEP
google-app-enginegoogle-cloud-datastore
KTB
KTB

Reputation: 1529

Locking mechanism at GAE

I'm working with a app that has both online datastore(GAE) and an offline datastore(HTML5 websql). So to resolve synchronizing problems, i'm trying to implement a locking mechanism. It should work like a semaphore, or as master-slave mechanism. User can get the lock, and if not available, can request for it. (although starvation is possible, it is handled by an user-policy)

So is there any facilities provided in App Engine to implementing this locking mechanism.

thanks in advance...

Upvotes: 1

Views: 553

Answers (1)

Peter Knego
Peter Knego

Reputation: 80330

There is no explicit mechanism for locking in GAE Datastore.

However, Datastore supports transactions, so you could create (for example) a SyncLock entity and set a property locked to true inside a transaction.

Note that creating a SyncLock is not covered by transaction, but updating an existing one is. So different sessions should try to access the same SyncLock entity and this can only be achieved if entities have the same ID. So you should use userID as ID for SyncLock.

Upvotes: 2

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