Re: fork()-safety, thread-safety

Hi,

On 2017-10-05 17:02:22 -0500, Nico Williams wrote:
> A quick look at the functions called on the child side of fork()
> makes me think that it's unlikely that the children here use
> async-signal-safe functions only.

That's not a requirement unless you're using fork *and* threads. At
least by my last reading of posix and common practice.

> - fork() is used in a number of places where execl() or execv() are
> called immediately after (and exit() if the exec fails).
>
> It would be better to use vfork() where available and _exit() instead
> of exit().

vfork is less portable, and doesn't really win us anything on common
platforms. On most it's pretty much the same implementation.

> vfork() is widely demonized, but it's actually quite superior
> (performance-wise) to fork() when all you want to do is exec-or-exit
> since no page copying (COW or otherwise) needs be done when using
> vfork().

Not on linux, at least not as of a year or two back.

I do think it'd be good to move more towards threads, but not at all for
the reasons mentioned here.

Greetings,

Andres Freund