Date: Sun, 5 Aug 2012 23:54:32 +0200 From: Jilles Tjoelker <jilles@stack.nl> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: system() using vfork() or posix_spawn() Message-ID: <20120805215432.GA28704@stack.nl> In-Reply-To: <20120730105303.GU2676@deviant.kiev.zoral.com.ua> References: <20120730102408.GA19983@stack.nl> <20120730105303.GU2676@deviant.kiev.zoral.com.ua>
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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
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