system() using vfork() or posix_spawn()

[Jilles Tjoelker]

On Mon, Jul 30, 2012 at 01:53:03PM +0300, Konstantin Belousov wrote:
> On Mon, Jul 30, 2012 at 12:24:08PM +0200, Jilles Tjoelker wrote:
> > People sometimes use system() from large address spaces where it would
> > improve performance greatly to use vfork() instead of fork().

> > A simple approach is to change fork() to vfork(), although I have not
> > tried this. It seems safe enough to use sigaction and sigprocmask system
> > calls in the vforked process.

> > Alternatively, we can have posix_spawn() do the vfork() with signal
> > changes. This avoids possible whining from compilers and static
> > analyzers about using vfork() in system.c. However, I do not like the
> > tricky code for signals and that it adds lines of code.

> > This is lightly tested.

> It is interesting to note that for some time our vfork(2) no longer
> stops the whole forked process (parent), only the forking thread is
> waiting for the child exit or exec. I am not sure is this point
> important for system(3), but determined code can notice the difference
> from the fork->vfork switch.

Neither fork nor vfork call thread_single(SINGLE_BOUNDARY), so this is
not a difference.

Thread singling may be noticeable from a failing execve() (but only in
the process doing execve()) and in the rare case of rfork() without
RFPROC.

-- 
Jilles Tjoelker