I have a dext that creates a periodic timer on its own dispatch queue. The callback is declared as follows: virtual void HandleTimer( OSAction *action, uint64_t time ) TYPE(IOTimerDispatchSource::TimerOccurred); The timer is allocated as follows: CreateActionHandleTimer( size, &ivars->TimerHandler ); IODispatchQueue::Create( "TimerQueue", 0, 0, &ivars->TimerDispatchQueue ); IOTimerDispatchSource::Create( ivars->TimerDispatchQueue, &ivars->TimerDispatchSrc ); I can start up the timer and it works just fine. However, in my Stop() method, when trying to shut the timer down, I get an assertion in OSAction::Cancel() for TimerHandler: Assertion failed: (queue), function Cancel, file uioserver.cpp, line 4401. What does this assertion indicate or is the source code available? If so, where? I'm using macOS 15.5. Note I am attempting to cancel the handler after the dispatch source and queue are canceled and the cleanup methods have been called (which is working). But, cancelling TimerHandler first also asserts.

After some experimentation with copying multiple DriverKit SDKs into /Applications/Xcode.app/Contents/Developer/Platforms/DriverKit.platform/Developer/SDKs/DriverKit, it's become clear that Xcode only supports the DriverKit version that ships with it. There is no way to configure an alternative SDK within a project and changing to a different one results in strange build warnings and errors. This begs the question - how are developers supposed to develop and support dexts? Here's one example scenario: SCSIDriverKit introduced a breaking change in DriverKit 24.4 (macOS 15.4 and Xcode 16.3) due to a new feature. Once a dext is built against that kit, it will not function on macOS 15.0-15.3 whether that feature is implemented or not. We found a similar thing with NetworkingDriverKit as well. So, over the course of maintaining a Sequoia product while working in Sequoia itself, simply updating Xcode breaks the product. Not to mention trying to maintain a Sequoia product in Tahoe when it is released. How is this a good developer experience? Are developers resigned to having a myriad of Xcode versions which may require booting into multiple macOS versions to use? That would in turn produce a myriad of product versions that would need to be deciphered by the user or an installer? Shouldn't developers be able to use the latest tooling while still being able to produce products for OSes that are just a year or two old? Or should DriverKit files be conditionalized so configuring a deployment version in Xcode actually builds the right thing even with the latest SDK? I just don't get it. Help me understand. Replacing kexts with dexts seems like a development nightmare.