Might as well start by saying: I have no idea. And that tends to mean that you'll not find anyone else on here capable of answering.
My experience with C++ is rather limited, though I do understand and have some experience with threading.
I'll understand if my saying as much precludes any response =P
That said, this actually isn't intended as a useless reply.. however much it may seem or prove to be.
You mentioned OpenMP working on various commercial compilers for years. I'm assuming you don't have a license for one of those compilers, resulting in the lack of (older versions of) GCC support being a problem?
And though I'll be attempting to look into the Boost and OpenMP libraries, I am curious:
What other implementations have you looked at?
How do you mean that they can't be used properly with object-oriented mechanics? (read: what are you looking for?)
And finally, given the results of my latest google searches and your post.. am I to understand that C++ doesn't have any core support for threading?
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Unbelievably awesomesauce to the absurd degree that I wet myself.
Who else has created a LW/magnets
so explicit the mods deleted a screencap of it? =P