Long story short: when I call exit() from a process started from QtConcurrent::run() it enters an infinite loop here:
Qt Code: 
  1. 0	pthread_cond_wait	pthread_cond_wait.S	162	0x00007ffff609459c	
  2. 1	wait	qwaitcondition_unix.cpp	87	0x00007ffff6a27a7b	
  3. 2	QWaitCondition::wait	qwaitcondition_unix.cpp	159	0x00007ffff6a27a7b	
  4. 3	QThreadPoolPrivate::waitForDone	qthreadpool.cpp	295	0x00007ffff6a1c808	
  5. 4	QThreadPool::~QThreadPool	qthreadpool.cpp	428	0x00007ffff6a1cfff	
  6. 5	QGlobalStaticDeleter<QThreadPool>::~QGlobalStaticDeleter	qglobal.h	1796	0x00007ffff6a1d695	
  7. 6	__run_exit_handlers	exit.c	78	0x00007ffff55ad045	
  8. 7	exit	exit.c	100	0x00007ffff55ad095	
  9. 8	fsElement::fsElement	fselement.cpp	41	0x000000000040b266	
  10. 9	fsElement::populateDirList	fselement.cpp	65	0x000000000040b70b	
  11. 10	fsElement::findFilesAndDirs	fselement.cpp	120	0x000000000040be77	
  12. 11	fsElement::findFilesAndDirs	fselement.cpp	122	0x000000000040be9c	
  13. 12	fsElement::findFilesAndDirs	fselement.cpp	122	0x000000000040be9c	
  14. 13	fsElement::findFilesAndDirs	fselement.cpp	122	0x000000000040be9c	
  15. 14	fsElement::findFilesAndDirs	fselement.cpp	122	0x000000000040be9c	
  16. 15	fsElement::findFilesAndDirs	fselement.cpp	122	0x000000000040be9c	
  17. 16	fsElement::findFilesAndDirs	fselement.cpp	122	0x000000000040be9c	
  18. 17	fsElement::findFilesAndDirs	fselement.cpp	122	0x000000000040be9c	
  19. 18	fsElement::findFilesAndDirs	fselement.cpp	122	0x000000000040be9c	
  20. 19	QtConcurrent::VoidStoredMemberFunctionPointerCall0<void, fsElement>::runFunctor	qtconcurrentstoredfunctioncall.h	216	0x000000000040adc4	
  21. 20	QtConcurrent::RunFunctionTask<void>::run	qtconcurrentrunbase.h	120	0x000000000040a396	
  22. 21	QThreadPoolThread::run	qthreadpool.cpp	106	0x00007ffff6a1ca4f	
  23. 22	QThreadPrivate::start	qthread_unix.cpp	248	0x00007ffff6a26a25	
  24. 23	start_thread	pthread_create.c	301	0x00007ffff608fc1a	
  25. 24	clone	clone.S	115	0x00007ffff5649a9d
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So I guess I shouldn't use exit() in this fashion. Is there some other way to exit a thread in this situation?

Bonus, longer question: I just want a way to perform some heavy i/o work and still keep the GUI up to date and responsive (I'm writing a file searching app as an exercise). Doing it in a seperate thread worked quite well, but I'd also like to have the ability to pause and cancel the work. Is threading the best way to do it? What should I do to do it right? QThread? QRunnable? Or is QtConcurrent the best way?