Re: [PATCH] _fwalk walks through thread local FILE pointer

["Joel Sherrill <joel at OARcorp dot com>" <joel dot sherrill at OARcorp dot com>]

My understanding of the reentrancy code in newlib must have gotten
totally out of sync with reality.  Is there any documentation
I can read to catch up and get educated again?

--joel

Jeff Johnston wrote:
> I think that the stdin/stdout/stderr for the thread should also be 
> walked in addition to the global list for now.  I don't think that 
> should cause problems with Cygwin but if so, we can add an #ifdef check.
>
> -- Jeff J.
>
> Thomas Pfaff wrote:
>
> > Take a look at findfp.c and you will see that all FILE pointers are 
> > hold in _GLOBAL_REENT, therefore _fwalk simply does not walk through 
> > the real FILE pointer list, but through the thread lokal ones which 
> > will contain only stdin, stdout and stderr.
> >
> > The obsolete REENT ptr can be removed but thats Jeffs decision.
> >
> > You can search the list why _GLOBAL_REENT was introduced some time 
> > ago. The former implementation where every thread has its own pointer 
> > list was incorrect, FILE pointers are process global objects.
> >
> > There is still a problem with stdin, stdout and stderr because every 
> > thread has its own buffers for these files. Cygwin has a workaround 
> > for this problem, it maps the thread lokal stdin, stdout and stderr to 
> > _GLOBAL_REENT aka _impure_ptr FILE pointers. I think that this will a 
> > working solution for other platforms as well.
> >
> > Thomas
> >
> > Joel Sherrill wrote:
> >
> > > This isn't right.  You are passed a REENT pointer and cannot
> > > simply ignore it.
> > >
> > > This will break any code that depends upon the existing
> > > behavior.  In RTEMS, we use _fwalk as it exists to
> > > implement sync() and walk each thread's open files.
> > > It is also used as part of the per-thread cleanup
> > > dynamically.
> > >
> > > If you want to have NULL ptr argument imply the global
> > > reent, great but don't break it.


--
Joel Sherrill, Ph.D.             Director of Research & Development
joel@OARcorp.com                 On-Line Applications Research
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