Hi, thanks for your answer and and video recommendation. Yes, I have the same impression that people are using GCD for everything. The sad part is that apple didn't stop the trend or at least to come with some videos, maybe something like GCD in depth, to make devs aware of the +/-. One result of this is that more and more forums have as accepted answers things like Never use NSLock, always use queue.sync from any synchronization without any explanation. I've read that os_unfair_lock is faster than pthread_mutex/NSLock, but as you mention it is a little problematic in swift. I've used in the past pthread_mutex, or std::mutex in C++ for UNIX-like, and they performed ok plus it is available in the UNIX-like world. Regarding the video, I think it is interesting. Please correct me if I'm wrong. I think the approach of this queue "tree" is a result of overuse dispatch/queues, too many threads created or blocked. They also emphasize to try to have queues per subsystem and not per class. Have a nice day :)