Watchdog killed the app because PrintKit is performing XPC operations on the main thread,see the call stacks below.
__dispatch_sema4_timedwait
__dispatch_semaphore_wait_slow
+[_PK_OneShotXPC withTimeout:doSyncronousOneShot:]
__pk_mdns_resolveSynchronous
-[PKPrinter(PKPrinterPrivate) resolveWithTimeout:]
-[PKPrinter printerURL]
-[UIPrinter _initWithPrinter:]
-[UIPrinterSelectionOption setPrinter:]
-[UIPrinterBrowserViewController tableView:didSelectRowAtIndexPath:]
-[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:isCellMultiSelect:deselectPrevious:performCustomSelectionAction:]
-[UITableView _userSelectRowAtPendingSelectionIndexPath:]
-[_UIAfterCACommitBlock run]
-[_UIAfterCACommitQueue flush]
__runAfterCACommitDeferredBlocks
__cleanUpAfterCAFlushAndRunDeferredBlocks
__UIApplicationFlushCATransaction
__UIUpdateSequenceRun
_schedulerStepScheduledMainSection
_runloopSourceCallback
___CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
___CFRunLoopDoSource0
___CFRunLoopDoSources0
___CFRunLoopRun
_CFRunLoopRunSpecific
_GSEventRunModal
-[UIApplication _run]
_UIApplicationMain
main main.m:26
start
