Re: [Qemu-devel] [PATCH] flush stdout after printing usage()

[Lionel Landwerlin]

Le mercredi 28 janvier 2009 à 23:06 +0200, Riku Voipio a écrit :
> On Wed, Jan 28, 2009 at 02:10:42PM -0600, Anthony Liguori wrote:
> > Riku Voipio wrote:
> > >testcase:
> > >
> > >qemu-arm|grep cpu
> > >
> > >Without fflush() getting output from piped qemu is a bit random.
> 
> > It should get flushed upon exit(). Perhaps the problem is that we're 
> > using _exit() instead of exit()?
> 

_exit does not trigger callbacks registred with at_exit.

from the man page :

       The function _exit() is like exit(3), but does not call  any  functions
       registered  with  atexit(3) or on_exit(3).  Whether it flushes standard
       I/O buffers and removes temporary  files  created  with  tmpfile(3)  is
       implementation-dependent.   On  the other hand, _exit() does close open
       file descriptors, and this may cause  an  unknown  delay,  waiting  for
       pending  output to finish.  If the delay is undesired, it may be useful
       to call functions like tcflush(3) before calling _exit().  Whether  any
       pending  I/O  is  canceled,  and which pending I/O may be canceled upon
       _exit(), is implementation-dependent.