https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80878
--- Comment #4 from admin_public at liblfds dot org --- I've had a look at the libatomic source code. Obviously, it's problematic to be sure you're understanding a large code base correctly when you go to it for the first time and you're looking something specific, so forgive me if I am here completely mistaken! I think I understand you Jonathan to mean that in the absence (by whatever means) of the native instruction, a replacement is provided, which has a different internal mechanism. >From what I can see in the libatomic code (and I may be completely wrong!), this internal mechanism under POSIX is a mutex. One of the advantages of lock-free data structures is that when properly written, they scale well. This advantage will absolutely and most certainly no longer exist if the native instruction is replaced by an alternative, as there are, as far as I know, no alternatives on any platforms which will continue to allow the scaling properties of the native instruction. In other words, libatomic is absolutely no use to lock-free data structures. This is not a fatal problem, as inline assembly can be used. (Also, lock-free data structures do not sleep, where a mutex can, and that does change the behaviour of the code, for there are some places in some kernels where you are not permitted to sleep.)
