However, I do not have the expertise to pore over assembly instructions, nor do I know whether this is the right approach. Assembler is the only way to access and set stack pointer, instruction
I would probably be just as happy with a slower safe cross-platform library built on OS support, as with the fast (dangerous?) assembly version. On UNIX ucontext_t is deprecated by the new POSIX standard (and might not be available in the next releases of C-libs). This has its reason in
Hello Gordon, thank you for your review - getting input/opinion of other people helps to shape the lib. Am 27.03.2011 14:48, schrieb Gordon Woodhull: pointer and the other registers. the fact that the interface of makecontext() function was designed before C99. It expects a function-pointer of void(*)() and accepts ellipses/var args for the arguments accepted by the function to be called by ucontext_t. I'm not the big C expert but I believe following cast is not legal (even if some compilers accept it): void my_fn( int, char *); (void(*)())my_fn; // not legal But the signature of ucontext-function makecontext( ucontext_t *, void(*)(), int, ...) requires this cast. Even worse - on x86_64/Linux the glibc the usage of non integer values as argument for the var-args is undefined. example: void my_fn( X * x); // to be called by ucontext X * x = new X("abc"); ucontext_t ctx; makecontext( & ctx, (void(*)())(my_fn), 1, x); // not reliable; undefined behaviour In the example above it might work (if the high bits of the address of x are zero) but in some cases makecontext() truncates the high bit of x pointer :/ => segfault Therefore I prefer the fcontext version over ucontext because it hasn't this problem. On Windows I suggest using the Windows Fiber version because as Holger mentioned I've to correct the exception handling.
I hope that people who know better, like Giovanni and Holger, will continue to help make the library more robust.
I hope it too :)
I thought I had understood from discussion that the class is moveable, but this didn't work for me. I ended up having to wrap contexts up in shared_ptrs in order to get my example to work (attached).
It was a misunderstanding the in review version boost::context is noncopyable - but it was in a previous version moveable (pimpl idiom). I currently modify the lib so that boost::context supports move operations.
The documentation is quite spare and completely lacks examples. It needs copy-editing (I can help there).
that would be really nice regards, Oliver