[poppler] UniqueFileStream and deleted files

[Albert Astals Cid]

El Diumenge, 24 de març de 2013, a les 14:03:49, Ihar `Philips` Filipau va 
escriure:
> On 3/24/13, Fabio D'Urso <fabiodurso at hotmail.it> wrote:
> >> On 3/23/13, Albert Astals Cid <aacid at kde.org> wrote:
> >> > Anyone with a mac to try?
> > 
> > I have an old powerpc-based mac with MacOSX 10.4 and it seems you can
> > delete
> > 
> > open files there too. I'm attaching the script I've used to test it.
> 
> Deleting an open files is an old *NIX feature. It appeared out of the
> fact that file can have many names. See man 2 link. On *NIX, unlink()
> doesn't delete the file - it deletes potentially one of its names.
> File is actually deleted when there are no more names referencing to
> it. On Windows, hard links/etc appeared much much later and it is now
> simply historical feature. (The difference is the reason why Linux can
> update itself mostly without reboots - but Windows can't.)
> 
> >> Just tried. Mac OS X doesn't have procfs.
> > 
> > Btw, I've found an interesting "pread" call in the man pages:
> >  ssize_t pread(int fd, void *buf, size_t count, off_t offset)
> > 
> > It is present both in Linux and Mac OS X.
> 
> pread() (and its sibling pwrite()) are old POSIX calls and are
> available literally everywhere.
> 
> If you want to use them in the MT context, you would have to maintain
> an offset variable per reader object, and update the offset variable
> after every read operation (since pread() doesn't update the filedes'
> internal offset). And code somewhere to actually close the file, after
> all the reader threads have terminated.

Can you have two reads from different threads simulatenously over the same fd 
with pread?

Cheers,
  Albert


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