[pron]

The Paul Turner approach works when you have up to about 10K-20K threads. Beyond that, you lose the ability to model a domain unit-of-concurrency (request/session) as a software unit of concurrency (thread). The kernel-thread approach works as long as you don't hit against the Little's Law wall. Basically, Little's Law tells you exactly when kernel threads become the wrong approach, which depends on the level of concurrency you wish to support and the mean latency of handling each concurrency unit (i.e. request/session).

> My second point is that there is one thread that this blocking-happy approach mostly doesn't apply to, and that is the UI thread.

You're not allowed to block the kernel UI thread, but you can schedule lightweight threads onto the UI thread and block them all you want, so from the programmer's perspective that restriction disappears.