Random crashes vs Swizzling

[choulepoka]

Hello there!

I have a curious story to tell, and perhaps this will be of use to somebody else in the Sentry Customer Community.

I have been tracking a random crash in our app for the last 2 years, the crash occurs when downloading a file locally (i.e.: URLSessionDownloadTask). Always seemed to be near the NSProgress update process, but the stack trace keep changing, and there are no references to any of our code.

I always assumed that this was caused by some obscure bug in our code, because the crash occurred randomly, and no matter what I did, what the user were using (device, OS version, app version), there would always be at least 1 or 2 daily occurence of these crashes.

Fast forward December 2023, where due to a bad merge conflict resolution, swizzling was disabled for Sentry, and it went live on the App store. (TLDR, no new build would be uploaded until mid January, where I could reactivate Swizzling)

However, much to my surprise, after almost 4 full weeks on the app store with the new version (with 90% upgrade rate for our user-base), there are zero crash for the last 4 weeks for that specific build. The users that did not upgrade to that specific build continued to experience the crashes, and the newest build that had the swizzling restored also started to exhibit the crashes too.

So I am tempted to permanently disabled Swizzling, even though I would loose some theoretically useful feature, but the fact is: I am only really interested by the crash reports

For anybody out there experiencing those random crashes, try disabling swizzling, it may help.

[philipphofmann]

@choulepoka, I'm sorry you experience random crashes when swizzling is enabled. Can you share some of them with us so we have to change to look into them and fix them?

We sometimes think about adding a guide or an extra package for auto-performance tracing that does not require the usage of swizzling. The downside is that it will require manual setup, but the benefit is no swizzling. Would you be interested in such a solution?