Race condition in ServiceObject.prototype.get

[jcking]

Environment details

• OS: Ubuntu 14.04
• Node.js version: v6.9.5
• npm version: 3.10.10
• google-cloud-node version: google-cloud@0.46.1 @google-cloud/pubsub@0.8.0

Steps to reproduce

This can be reproduced under specific conditions when using the "get or create" functionality described in ServiceObject.protoype.get() with { autoCreate: true }. I discovered it while using the pubsub API. If you run 2 ServiceObject.protoype.get() at the same time with the same arguments for a resource that does not exist prior, it is possible for one to succeed and the other to fail. This does not seem like intended behavior to me.

1. Request 1 -> get
2. Request 2 -> get
3. Request 1 <- 404 Not Found
4. Request 2 <- 404 Not Found
5. Request 1 -> create
6. Request 1 <- 200 OK
7. Request 2 -> create
8. Request 2 <- 409 Conflict

If these requests occur in different orders it is possible for both to pass or one to fail and the other pass.

Thoughts?

I have a proposed fix that modifies the ServiceObject.prototype.get() when { autoCreate: true } that wraps the call to ServiceObject.prototype.create() to re-run ServiceObject.prototype.get() with { autoCreate: false } if a 409 Already Exists error is detected on the call to ServiceObject.prototype.create().

[stephenplusplus]

Sounds good!

[jcking]

@stephenplusplus I also noticed service-object.js#L221 and service-object.js#L225 pass metadata as the third argument, however the documentation states the third argument to the callback should be the apiResponse. Are these equivalent or do you want me to modify it to be the apiResponse as well?

[stephenplusplus]

Yep, metadata is actually the apiResponse. Thanks for the help!

[danoscarmike]

@stephenplusplus can this one be closed now?