Apple released GCD a two years ago. GCD is a basically parallel programming toolkit, with super-efficient, lightweight asynchronous tools, like dispatch queues, semaphores, asynchronous I/O tools etc. Here is the reference:
I have created a patch, that uses dispatch_semaphore_t instead of pthread_mutex_t in Standard_Mutex, and it seems to give some performance improvement over the phtread_mutex implementation. I have attached the patch for further examination.
The other thing where it can be useful, is the replacement of Intel TBB parallel_for_each, with dispatch queues, they can be easily implemented, reducing the 3rd party dependencies of OCCT. I also attached a simple implementation of it. It uses std::function, which is a C++11 feature, but C++11 is supported by Apple since 10.7+ and iOS 5.0+, so this should not be a problem. Otherwise, it can be rewritten work just like TBB's parallel_for_each.
These should not be considered as tested, and reviewed codes, these rather ideas, and suggestions for using this state of the art technology where it is available.
PS.: I could not attach the file, becasue only "jpg jpeg gif png txt doc xls pdf ppt pps odt ods odp" files are allowed (why?) so here is it: