AB tests not working when sending activation event right after activating remote config #3687
Description
[REQUIRED] Step 2: Describe your environment
- Xcode version: 10.3
- Firebase SDK version: 6.6.0
- Firebase Component: Remote Config/AB Testing
- Component version: 4.2.1/3.0.0
[REQUIRED] Step 3: Describe the problem
We have an ongoing issue since last year where activating an experiment (i.e. sending an activation event) exactly after calling [[FIRRemoteConfig remoteConfig] activateFetched] didn't work. That is because activateFetched presumably did some property setting related to AB tests in the background. We figured that out by logging firebase messages to the console.
We found that also to be the case because doing this
[[FIRRemoteConfig remoteConfig] activateFetched];
// This is a workaround for A/B tests not working when the activation event is sent too soon after `activateFetched`.
// Basically we delay further UI initialization and Analytics event dispatch enough that Firebase AB Testing framework has
// time to set-up a conditional user property internally used for marking ab test behaviour with activation event.
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
// send activation event here
});
made it work. But obviously this is not the way we wan't to use the API.
We were thrilled to see that fetchAndActivateWithCompletionHandler which should have async completion was added. But it seems the issue is still not fixed. AB tests still don't get activated.
I was looking at the newly open sourced code of Remote Config and AB testing and I think I can pin point the problem:
**fetchAndActivateWithCompletionHandler** calls **activateFetched** which in turn calls **activateWithCompletionHandler**
**activateWithCompletionHandler** calls **[strongSelf updateExperiments]** which does not have a completion handler but if you follow the updateExperiments method down the rabbit hole you'll find a call like this in **FIRExperimentController**
- (void)updateExperimentsWithServiceOrigin:(NSString *)origin
events:(FIRLifecycleEvents *)events
policy:(ABTExperimentPayload_ExperimentOverflowPolicy)policy
lastStartTime:(NSTimeInterval)lastStartTime
payloads:(NSArray<NSData *> *)payloads {
FIRExperimentController *__weak weakSelf = self;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
FIRExperimentController *strongSelf = weakSelf;
[strongSelf updateExperimentsInBackgroundQueueWithServiceOrigin:origin
events:events
policy:policy
lastStartTime:lastStartTime
payloads:payloads];
});
}
which as you can see calls something on the background queue and it isn't synched to the original activateWithCompletionHandler.
Steps to reproduce:
-
Create an AB test that requires an activation even
-
Call fetchAndActivateWithCompletionHandler and in the completion block send the activation event
Relevant Code:
[[FIRRemoteConfig remoteConfig] fetchAndActivateWithCompletionHandler:^(FIRRemoteConfigFetchAndActivateStatus status, NSError * _Nullable error) {
if (error) {
return;
}
[FIRAnalytics logEventWithName:@"ActivationEvent" parameters:nil];
}];