Tcl Source Code

According to the standard for dlerror(), it's not required to be thread-safe.  
http://www.opengroup.org/onlinepubs/009695399/functions/dlerror.html

I also checked several open source libc.  NetBSD and OpenBSD don't use thread-specific storage for dlerror messages, but the GNU/Linux glibc does.

Attached is a patch to fix the problem.  It drains the dlerror() first after entering the critical region.

The Linux usage suggested is slightly different than what BSD seems to suggest.  The glibc dlsym manual suggests using dlerror to indicate the success or failure of a dlsym(), rather than NULL from the return of dlsym(), because apparently dlsym() can return 0/NULL and still have succeeded (with some symbols).  So the logic should probably be changed further based on what the glibc docs say.

This is the example taken from the manual for dlsym:
 dlerror();    /* Clear any existing error */
 cosine = dlsym(handle, "cos");
 if ((error = dlerror()) != NULL)
   ...
  

I also added error handling to TclpFindSymbol().  It appears to be unfinished prior to this, or the usage expectations of it have changed, because in the HEAD it doesn't use the interp argument to report an error like the (outdated?) comments state.

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In functions like TclLoadFile and TclpLoadFile, TclpFindSymbol()
is used multiple times and is not expected to modify the interp
result. At least those functions need to be modified to reset
the interp result after the last TclpFindSymbol() call.

Further on, the same modification will be needed in tclLoadDyld.c
as well (if the Mac-implementation is not thread-safe), and the
TclpFindSymbol change is needed in tclLoadNext.c, tclLoadOSF.c,
tclLoadShl.c and tclWinLoad.c as well.

In practice, I doubt that this ever will be a practical
problem, because normally all libraries are loaded in a
single thread at start-up. But - strictly speaking - yes,
I agree that the mutex should be there and TclpFindSymbol
should leave an error-message in interp result as documented.

Regards,
            Jan Nijtmans

File Added - 278384: tclLoadDl-2.patch