> `dispatch_semaphore/dispatch_sync` blocks the thread instead of yielding asychronously (can cause "thread explosion") dispatch_group can do waits without blo

> `dispatch_semaphore/dispatch_sync` blocks the thread instead of yielding asychronously (can cause "thread explosion") dispatch_group can do waits without blocking threads, but asynchronicity is overrated, and dispatch's design makes it easy to overdo. Having default global concurrent queues was probably a mistake. Swift concurrency is a more modern design here.