Data inconsistency in the Google+ Hangout App shared data object? - google-plus

Question

I'm getting inconsistent results when setting and getting values using submitDelta, setValue, clearValue, and getState. It appears that these are asynchronous methods, so my synchronous commands (e.g., console.log) execute using a local data object. Then eventually the shared data object updates and in turn updates the local data object. Is this a correct assessment? Is there a way to run these data commands synchronously, i.e., wait for the shared data object to update before moving on in the program?

Answer 1

Yes, data operations in the Hangouts API are asynchronous. To achieve synchronicity you would have to listen to onStateChanged events and only continue whatever you are doing in those events.
The event will be called for all participants, also the local participant that triggered the change.

Answer 2

It doesn't look possible to write synchronous shared data object calls because if you have more than one onStateChange in your code, they all fire together. In other words, I can't tie one shared data object update to one onStateChange.
It looks like Google+ Hangouts executes database APIs in this order:
Getting and setting values in the local data object (using getState)
Getting values from the shared data object using getState.
Changing values in the shared data object (setValue, clearValue, submitDelta, etc.).
onStateChange to listen for shared data object changes.
The following (pseudo)code
setValue('counter', '11')
getValue('counter')
onStateChanged (getValue('counter'))
submitDelta( {'counter': '22'} )
getValue('counter')
onStateChanged (getValue('counter'))
clearValue('counter')
getValue('counter')
onStateChanged (getValue('counter'))
submitDelta( {'counter': '33'} )
getValue('counter')
onStateChanged (getValue('counter'))
would return
undefined
undefined
undefined
undefined
33
33
33
33
33
33
33
33
33
33
33
33
33
33
33
33
because the four getValues execute first, then setValue, submitDelta, clearValue, and submitDelta execute, then the four onStateChanged execute together, four times each because the shared data object is changed four times.
Does that sound right?