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Date: Tue, 21 Jul 2009 16:05:02 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: close on exec atomics
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On Jul 21 15:58, Corinna Vinschen wrote:
> On Jul 21 07:04, Eric Blake wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > It seems like it would be pretty easy to add several new close-on-exec
> > features required by POSIX 2008:
> > 
> > open(name, O_RDONLY | O_CLOEXEC);
> > // skips the need to use fcntl
> > 
> > fcntl(fd, F_DUPFD_CLOEXEC);
> > // like F_DUPFD, but closes window without having to use
> > // fcntl(fd, F_SETFD, fcntl(fd, F_GETFD))
> > 
> > and those provided by glibc as extensions:
> > 
> > fopen(name, "re");
> > // like fopen "r", but with cloexec set
> > 
> > The argument is that in multi-threaded apps, if one thread opens a file
> > but has not yet turned on the close-on-exec bit while another thread does
> > a fork-and-exec, then you leaked the fd into the child; and these new
> > flags close the window.
> > 
> > Should I go ahead and prepare a patch for the newlib side?
> 
> It's not that easy to implement, especially not the fcntl which requires
> to redefine the dup2 methods throughout to allow atomic operation on the
> target OS handles.  open (O_CLOEXEC) is much easier.  Anyway, can we
> wait until after Cygwin 1.7.1?

...which is to say, I added it to my TODO list.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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