There are two issues in this case:
1. XPC messages are processed in a private queue making OEDeviceManager calls unsafe when retrieving device handlers. We solve this problem by making thread safe operations.
2. Sometimes we may receive binding updates on the emulator process before the process has had the time to recognize a device that is connected. This is solved by using placeholder device objects that we replace with real devices in OEHIDEvent when the device is finally parsed. This is possible because if a device is added to the UI process it will be added to the emulator process eventually.
clobber
Christoph Leimbrock
Kyle Lacy
Remy Demarest