I've recently had issues debugging the Universal Link functionality of my app.
I was able to get deep linking to work but it seemed to only work 10% of the time. Since I had just updated to iOS 12, I wanted to make sure there was nothing else I had to do as a developer to ensure the feature worked.
So what was causing intermittent failure?
It seems that iOS has a somewhat strict policy engine for determining when background threads can run.
I was able to observe this by USB tethering to my phone and opening up the debug console for my device
- Xcode –> Windows –> Devices & Simulators
- Click on device in the left pane
- Click Open Console
From there, I was able to filter on "swcd" (SharedWebCredential Daemon). Keeping this console open, I was able to see the daemon at work during app install which is when iOS attempts to pull down the apple-app-site-association file for my app.
As it turns out, dasd (DuetActivitySchedulerDaemon) was failing to run the SharedWebCredential Daemon because my phone had restarted recently, then later it was determined that my phone was too hot...
e.g.
{name: ThunderingHerdPolicy, policyWeight: 1.000, response: {Decision: Must Not Proceed, Score: 0.00, Rationale: [{deviceInUse == 1 AND timeSinceThunderingHerdTriggerEvent < 900}]}}
], FinalDecision: Must Not Proceed}
{name: ThermalPolicy, policyWeight: 5.000, response: {Decision: Absolutely Must Not Proceed, Score: 0.00, Rationale: [{thermalLevel >= 20}]}}
], FinalDecision: Absolutely Must Not Proceed}
Developers beware!
