[xml] calling xmlCleanupParser from a library considered harmful

[Michael Stahl <mstahl redhat com>]

hi all,

authors of libraries that use libxml2 internally for whatever reason
should take note that calling xmlCleanupParser frees various bits of
global state and as a result makes libxml2 effectively unusable for any
other code in the process that also happens to use libxml2, and hence
makes your library effectively un-usable (until the offending call is
patched out).

http://www.xmlsoft.org/html/libxml-parser.html#xmlCleanupParser

> This function name is somewhat misleading. It does not clean up 
> parser state, it cleans up memory allocated by the library itself.
> It is a cleanup function for the XML library. It tries to reclaim
> all related global memory allocated for the library processing. One
> should call xmlCleanupParser() only when the process has finished
> using the library [...] WARNING: if your application is
> multithreaded or has plugin support calling this may crash the
> application if another thread or a plugin is still using libxml2.
> [...]

please do not _ever_ call xmlCleanupParser from a library.

LibreOffice has been hit for the second time[1] now by some library
calling xmlCleanupParser; a colleague much smarter than me wasted many
hours tracking that down as the root cause of an obscure crash involving
CUPS and thread local storage... which finally motivated me to add this
hack (should work on ELF platforms) so the next time the problem is
easier to detect:

http://cgit.freedesktop.org/libreoffice/core/commit/?id=d68113f3229d0ec8c84f77dcac3b64a3fd7e03e4

regards,
 michael

[1] pedantic note: technically at the first time it was OpenOffice.org