2017.07.05 15:02 "Re: [Tiff] A bug in libtiff error/warning handling", by Olivier Paquet

2017-07-05 9:57 GMT-04:00 Paavo Helde <paavo@osa.pri.ee>:

On 5.07.2017 15:40, Olivier Paquet wrote:

By the way, thread local storage is a poor solution as it does not handle the case of several unrelated libraries using libtiff from within the same thread.

This can be made to work if the client library installs and restores the handlers each time before/after any call to libTIFF. Yes that's tedious but better than the current state. Better fixes would mean API changes, like adding error/warning pointers to an enhanced version of TIFFClientOpen().

Yes, it would require API changes but I think they are needed. I don't think we should add a dependency to get thread local storage which provides only half a fix when there is a better fix which does not require it. Both require changes to client code anyway.

Besides, it would also break some stuff. I'm fairly certain our own code sets the error handler only once and expects it to be used by multiple threads. I doubt we're the only ones doing that. A new version of TIFFClientOpen() would allow that to keep working.

The other thing to be decided is if we want to push the idea further to have a library handle so we can also fix TIFFRegisterCODEC(), TIFFSetTagExtender(), etc. Such a handle could hold all currently global data and would be given to the new TIFFOpen. A little more complexity but also potentially a more complete long term fix.

Olivier