In user space? None, but if the processors aren't doing any other work and your threads are the only available runnable threads then they're likely to get run. As cores become more numerous, the problem will be keeping them occupied. That's why Intel and AMD want you to start writing multi-threaded code. NOW! You're making them look bad with all those cores doing nothing. :)
They (Intel and AMD) keep saying that. If there's an elite few, it's because there are damn few jobs that require that as a primary skill. Other skills are more important as primary skills and if you have those you don't need threading skills. You'd be better off investing in those other skills.
This is probably true,but if you are a server side programmer, then its useful to keep in mind that programming for multiple processors will be a necessary skill to know in the future and learn whatever little's possible.
That future remains elusively out of reach. I've been doing multi-threaded programming for over two decades and lock-free algorithms nearly as long and it's just as marginal now as it was then.
