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November 2004
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2004.11.05 00:40 "Re: is libtiff thread-safe?", by Bob Friesenhahn
On Fri, 5 Nov 2004, Joris wrote: > > Documenting that issue and suggesting that the callbacks contain a > > mutex or critical section (if thread safety is an issue) might be a > > good idea. > > I totally fail to see the connection between the lack of TIFF * parameter in the > callbacks on the one hand, and multi-threading on the other. The callbacks are In that case I will attempt to educate you. > called in the same thread context as the call to LibTiff in which the error > occured. There's no threading issue here. There is a threading issue because the thread which experiences the error is also the one which would normally make use of the detailed error information. When the code which invoked a libtiff function returns, it needs to be able to retrieve the error information so that it can properly inform the user. That means that the libtiff warning/error callback must store the error info in some thread-specific place so that it may be retrieved once the libtiff function returns. If the functions provided a pointer to user context then the error information could simply be stored there, without any need to use an OS-specific thread-API function to support thread-specific storage. Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us http://www.simplesystems.org/users/bfriesen