On Wed, 17 Dec 2008, Guy K. Kloss wrote: > >> If you are using an object oriented >> language and lcms supports passing a pointer then you can pass the >> address of 'this' object and the callback function can then invoke a >> well known method name on the object so that the error is handled by >> the correct object. This avoids any use of a global variable. > > But it would still require registering a callback target (or object that has > got a target)? If so, then competing calls in a multi threaded application > could potentially result in a misdirected error callback invocation.
It is true that with this approach only one C callback function can be registered at one time. Via inheritance, several different types of objects can simultaneously use lcms. If lcms was written in C++ then it could provide a base class for callback objects (avoiding a global registration entirely) but since it is written in C, a function with C-language binding needs to then invoke a C++ class method (or dispatch to Python, Perl, etc). The other solution is to not use a callback at all and rely entirely on data stuffed into a user supplied error report buffer. This makes it difficult to do things like aborting further processing unless the desired behaviors can be fully parameterized. There is the option of a mixed solution where both a buffer and a callback function are passed for each call to lcms, and the callback function is provided with a pointer to the buffer. Bob ====================================== Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ ------------------------------------------------------------------------------ SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
