Comment by theK
1 day ago
Didn't he just say that fork turns out to be comparatively faster to the non-fork samples we get? Ie Linux spawns processes faster than Microsoft's kernels?
1 day ago
Didn't he just say that fork turns out to be comparatively faster to the non-fork samples we get? Ie Linux spawns processes faster than Microsoft's kernels?
Didn't I just say that "the problem with fork isn't really that it's slow"? It's all the other OS design choices it forces on you if you want it to be fast.
Right, you did. I somehow misread your comment.
We don't have any broadly used non-fork samples. Windows, macOS, and Linux all have fork. So the presence of fork can't be the reason for the performance difference.
(Windows's fork is called ZwCreateProcess)
MacOS has posix_spawn. See https://developer.apple.com/library/archive/documentation/Sy... (yes, that’s an iOS man page. MacOS has the call, too, but I couldn’t find the man page online and it looks identical to me)
I don’t know how they implemented it, though. Under the hood, it could do the equivalent of a fork/exec pair.
XNU is open source; here’s a link into the middle of the implementation, after it’s copied all the necessary attributes of the parent into the new process structure: https://github.com/apple-oss-distributions/xnu/blob/f6217f89...
XNU's posix_spawn implementation is not fork/exec-based. It does roughly what the API suggests it would do.
NtCreateProcess does not implement a forking model. It is analogous to posix_spawn.
If you pass null for the section handle, it shares pages with the calling process, thus implementing a forking model. Or at least the parts of a forking model that some people erroneously believe are responsible for performance differences.