[libvirt] RFC: Use __attribute__ ((cleanup) in libvirt ?

For those who don't already know, GCC and CLang both implement a C language extension that enables automatic free'ing of resources when variables go out of scope. This is done by annotating the variable with the "cleanup" attribute, pointing to a function the compiler will wire up a call to when unwinding the stack. Since the annotation points to an arbitrary user defined function, you're not limited to simple free() like semantics. The cleanup function could unlock a mutex, or decrement a reference count, etc This annotation is used extensively by systemd, and libguestfs, amongst other projects. This obviously doesn't bring full garbage collection to C, but it does enable the code to be simplified. By removing the need to put in many free() (or equiv) calls to cleanup state, the "interesting" logic in the code stands out more, not being obscured by cleanup calls and goto jumps. I'm wondering what people think of making use of this in libvirt ? To my mind the only real reason to *not* use it, would be to maintain code portability to non-GCC/non-CLang compilers. OS-X, *BSD and *Linux all use GCC or CLang or both, so its a non-issue there. So the only place this could cause pain is people building libvirt on Win32, who are using the Microsoft compilers instead og GCC. IMHO, it is perfectly valid for us to declare that MSVC is unsupported with Libvirt and users must use GCC to build on Windows, either natively via cygwin, or cross-build from Linux hosts. As an example of what it would involve... This commit enables the basic helper macros in libguestfs: https://github.com/libguestfs/libguestfs/commit/98b64650c852ccc9a8eef8b96... These commits make use of them https://github.com/libguestfs/libguestfs/commit/61162bdce1a00a921a47eb3e7... https://github.com/libguestfs/libguestfs/commit/5a3da366268825b26b470cde3... https://github.com/libguestfs/libguestfs/commit/791ad3e9e600ef528e3e5a8d5... Finally, I'm absolutely *not* volunteering to actually implement this idea myself, as I don't have the free time. I just want to raise it as a discussion item, and if we agree its something we'd do, then we can make it a GSoC idea, or let any other interested person hack on it at will. There's no need for a "big bang" convert everything approach, we can do it incrementally. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|