How do you implement Coroutines in C++

There's no easy way to implement coroutine. Because coroutine itself is out of C/C++'s stack abstraction just like thread. So it cannot be supported without language level changes to support.

Currently(C++11), all existing C++ coroutine implementations are all based on assembly level hacking which is hard to be safe and reliable crossing over platforms. To be reliable it needs to be standard, and handled by compilers rather than hacking.

There's a standard proposal - N3708 for this. Check it out if you're interested.

For posterity,

Dmitry Vyukov's wondeful web site has a clever trick using ucontext and setjump to simulated coroutines in c++.

Also, Oliver Kowalke's context library was recently accepted into Boost, so hopefully we'll be seeing an updated version of boost.coroutine that works on x86_64 soon.

On POSIX, you can use makecontext()/swapcontext() routines to portably switch execution contexts. On Windows, you can use the fiber API. Otherwise, all you need is a bit of glue assembly code that switches the machine context. I have implemented coroutines both with ASM (for AMD64) and with swapcontext(); neither is very hard.

Yes it can be done without a problem. All you need is a little assembly code to move the call stack to a newly allocated stack on the heap.

I would look at the boost::coroutine library.

The one thing that you should watch out for is a stack overflow. On most operating systems overflowing the stack will cause a segfault because virtual memory page is not mapped. However if you allocate the stack on the heap you don't get any guarantee. Just keep that in mind.