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> Hi,
> As a disclaimer, I'm a FreeBSD developer interested in making sure we're doing the right thing here. =)
> May I ask what the above assessment is based on, and specifically what we need to address?
Hello, Kyle! That assessment is based on my quick and incorrect reading of posix_spawn source code. I didn't notice that "error" is visible in the parent due to address space sharing. Sorry for that, and thank you for the correction. A proper error notification is required for posix_spawn to be used in subprocess as a replacement for fork/exec, and FreeBSD does it right.
While we're here, would you be kind to answer several questions about posix_spawn on FreeBSD?
1) On Linux, without taking additional precautions, signals may be delivered to a child process created via vfork(). If a signal handler runs in such a child, it can leave traces of its work in the (shared) memory, potentially surprising the parent process. To avoid this, glibc[1] and musl[2] disable all signals (even signals used internally for thread cancellation) before creating a child, but FreeBSD calls vfork() right away. Is this not considered a problem, or is something hidden in vfork() implementation?
2) Another problem with vfork() is potential sharing of address space between processes with different privileges (see Rich Felker's post[3] about this and the previous problem). Is this a valid concern on FreeBSD?
3) Does FreeBSD kernel guarantee that when waitpid(WNOHANG) is called at [4], the child is ready for reaping? On Linux, it's not always the case[5].
[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/spawni.c;h=353bcf5b333457d191320e358d35775a2e9b319b;hb=HEAD#l372
[2] http://git.musl-libc.org/cgit/musl/tree/src/process/posix_spawn.c?id=5ce3737931bb411a8d167356d4d0287b53b0cbdc#n171
[3] https://ewontfix.com/7
[4] https://svnweb.freebsd.org/base/head/lib/libc/gen/posix_spawn.c?view=markup#l229
[5] https://sourceware.org/git/?p=glibc.git;a=commit;h=aa95a2414e4f664ca740ad5f4a72d9145abbd426