[poppler] UniqueFileStream and deleted files

[Albert Astals Cid]

El Diumenge, 24 de març de 2013, a les 06:32:46, Thomas Freitag va escriure:
> Am 23.03.2013 20:08, schrieb Albert Astals Cid:
> > El Dissabte, 23 de març de 2013, a les 20:01:58, Thomas Freitag va 
escriure:
> >> Am 23.03.2013 18:59, schrieb Ihar `Philips` Filipau:
> >>> On 3/23/13, Ihar `Philips` Filipau <thephilips at gmail.com> wrote:
> >>>>> (i tried to find a way to duplicate a FILE* but failed)
> >>>> 
> >>>> How did you duplicate FILE*?
> >>>> 
> >>>> How did the `fdopen( fileno(oldfile), mode )` failed?
> >>> 
> >>> Nope. This is the right way:
> >>> 
> >>> int new_fd = dup( fileno(oldfile) );
> >>> FILE *new_file = fdopen( new_fd, mode );
> >> 
> >> Duplicating the FILE pointer in that way is not a solution: I tried it
> >> that way when I began to implement thread safe feature: At least under
> >> Ubuntu and gcc the duplicated file pointer uses the same underlying
> >> buffer, and that corrupts the thread safe feature.
> > 
> > Exactly, it is the documented behaviour
> > 
> > "They refer to the same open file description and thus share file offset"
> > 
> >> That's why I used the
> >> fileName to create a complete new file pointer.
> >> Of course we can do it in that way if we detect that the file is deleted
> >> (and only then!), but a program which use threads to render different
> >> pages the same time will then render garbage :-(
> > 
> > No. We either write the file back to a temporary location as i suggested
> > in my initial mail, or use the only fd with locking. I think i'm favoring
> > the second use case since writing the file back might not even work if we
> > run out of free space.
> 
> I think, You're second solution is quite easy to implement (I mean
> really only easy to implement, it will take some time to change every
> code snippet and deeply test the changed code): since FileStream already
> use it's own buffer, there is no really need of the underlying system
> file buffer. So implementing something like a sharable GooFile (or
> extend gfile) which can be locked and remember the next read position in
> FileStream and then do something like gfile->read(readposition, buf,
> buflength) wouldn't really reduce the speed. But then I would prefer use
> the low level file handles instead of the file pointer. And it's even
> better than to write platform specific code and rely on Windows that the
> open file is not deletable and search for a Mac solution.
> Then the UniqueFileStream mechanism and the streamOwner instance
> variable can be removed, too.
> On the other hand: who deletes a just opened file and expects stability
> of the application which just opens the file? Is it really worth the effort?

It is a fairly typical use case. Open a file you just downloaded temporarily 
with firefox or your mail client and then close firefox/mail client, the 
"correct" behaviour is the firefox/mail client to clean up the temporary files 
they created, but i still want okular to work on that file.

Cheers,
  Albert

> 
> Cheers,
> Thomas
> 
> > Cheers,
> > 
> >    Albert
> >> 
> >> Cheers,
> >> Thomas
> >> 
> >>> It is OK to use *NIX function here - the dup() - since deleting open
> >>> file can happen only on the *NIX-like OS, Mac OS X included. Windows
> >>> doesn't allow that. Correct me if I'm wrong. Tested on Linux, HP-UX
> >>> and Solaris for the safety sake: the fclose() would close the dup()ed
> >>> file descriptor.
> >>> 
> >>> Though I'm not sure how to integrate that with the rest of the portable
> >>> code. :)
> >>> 
> >>> FYI.
> >>> _______________________________________________
> >>> poppler mailing list
> >>> poppler at lists.freedesktop.org
> >>> http://lists.freedesktop.org/mailman/listinfo/poppler
> >>> 
> >>> .
> >> 
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> > 
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> > .
> 
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