I made https://github.com/rubenvannieuwpoort/atomic-exchange for my usecase.
You're misinterpreting the title. The author didn't intend "Unix" to literally mean only the official AT&T/TheOpenGroup UNIX® System to the exclusion of Linux.
The first sentence of "UNIX-like" makes that clear : >This is a catalog of things UNIX-like/POSIX-compliant operating systems can do atomically,
Further down, he then mentions some Linux specifics : >fcntl(fd, F_GETLK, &lock), fcntl(fd, F_SETLK, &lock), and fcntl(fd, F_SETLKW, &lock) . [...] There is a “mandatory locking” mode but Linux’s implementation is unreliable as it’s subject to a race condition.
There's also `flock`, the CLI utility in util-linux, that allows using flocks in shell scripts.
POSIX file locking semantics really are broken beyond repair: https://news.ycombinator.com/item?id=46542247
What else it does not do is a transaction with multiple objects. That is why, I would design a operating system, that you can do a transaction with multiple objects.
https://learn.microsoft.com/en-us/windows/win32/fileio/about...
mv a b
mv c d
If that's not what you're saying, could you give an example of something you want to be able to do but can't?
You can remedy 2) by doing fsync() on the parent directory in between. I just asked ChatGPT which directory you need to fsync. It says it's both, the source and the target directory. Which "makes sense" and simplifies implementations, but it means the rename operation is atomic only at runtime, not if there's a crash in between. It think you might end up with 0 or 2 entries after a crash if you're unlucky.
If that's true, then for safety maybe one should never rename across directories, but instead do a coordinated link(source, target), fsync(target_dir), unlink(source), fsync(source_dir)
Just git branch (one branch per region because of compliance requirements) -> branch creates "tar.gz" with predefined name -> automated system downloads the new "tar.gz", checks release date, revision, etc. -> new symlink & php (serverles!!!) graceful restart and ka-b00m.
Rollbacks worked by pointing back to the old dir & restart.
Worked like a charm :-)
that's how Chrome updates itself, but without the symlink part
The OS core is deployed as a single unit and is a few GB in size, pretty small when internal storage is into the hundreds of GB.
With that said, at least for C and C++, the behavior of (std::)atomic when dealing with interprocess interactions is slightly outside the scope of the standard, but in practice (and at least recommended by the C++ standard) (atomic_)is_lock_free() atomics are generally usable between processes.