Good afternoon friends!
Can't figure out why metricKit doesn't send MXDiagnosticPayload reports right away? But only once every 24 hours
"The system then delivers metric reports at most once per day, and diagnostic reports immediately in iOS 15 and later and macOS 12 and later." - Apple Documentation
iPhone 7, iOS 15
I reverse-engineered MetricKit to get to the bottom of this. The short version is that in practice there is a "probationary period" before you get your first MXDiagnosticPayload. I suspect this is some confusion on MetricKit's part about what payloads are delivered in realtime vs what are on a 24-hour basis, but it could also be a feature.
To reproduce the "not delivered" behavior, install an app with a new bundle ID never seen before, it won't get crash reports. To reproduce the "delivered in real-time behavior", charge the device to 100%, reboot it while plugged in, and leave it locked on your desk for 15 minutes, crash reports occurring after that will be delivered in real time.
Behind the scenes, failed crash deliveries will log statements like
default 05:37:23.812310-0500 ReportCrash [bundle id] is not a MetricKit client
This is true even though, when calling MXMetricManager.shared.add(subscriber), metrickitd logs that you are a client.
The discrepancy seems to happen because some step inbetween these processes is disintermediated by duet scheduler (dasd). duet considers factors like "is the device being used?" and "didn't we do this a few minutes ago?" when deciding to give cputime to tasks. So if you are currently testing this behavior, or troubleshooting why it works in one app and not in another, that actually changes the behavior which makes it very hard to understand or troubleshoot.
Following the instructions from @drewcrawford works - crash diagnostics are delivered to apps immedately after they relaunch and register a subscriber.
Hang diagnostics, though, never seem to be delivered - at least not for simple cases of blocking the main thread for 5 seconds. Does anyone have insights into why they are not being received?