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This can be implemented without assembly using setcontext/getcontext on POSIX-compatible systems, and GetThreadContext/SetThreadContext on Windows.

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Examples of that in the Io source:

https://github.com/stevedekorte/io/blob/master/libs/coroutin...

Not if you care for performance.

get/setcontext do not copy stack, but use an allocated bit of memory space for the stack and swaps stack pointers just like this implementation. I don't see how that's a performance hit.

I do not pretend to know about Windows internals so I won't comment on Windows.

The author of boost.context did some benchmarking[1] and found that get/setcontext was an order of magnitude slower than a custom solution. Whether this matters is an entirely different question, but it's clear that get/setcontext has some overhead.

[1] http://www.boost.org/doc/libs/1_54_0/libs/context/doc/html/c...

See also the notes on various implementation mechanisms of libcoro ( http://cvs.schmorp.de/libcoro/coro.h )

getcontext and setcontext also keep track of signal state, which involves a syscall.

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