The tasks that the blog mentions are serviced by a background thread pool where possible. Only a certain number of threads can be spun up in that pool because we don’t want to “swamp” the CPU by spinning up too many.

If a task which might otherwise be serviced by that thread pool needs work and the maximum allowed threads are currently being used to do other things, then the threadpool message gets thrown and there is no “hand off” to the threadpool – the work gets done on the CURRENT thread.

So yeah, we’re dealing with threads and therefore the CPU, but it doesn’t necessarily mean the CPU is under pressure…just that we’ve maxxed out the background threadpool.