Re: [xml] Threads and statically linked libxml2 in a plugin

[Daniel Veillard <veillard redhat com>]

On Thu, Mar 30, 2006 at 02:14:49PM +0200, Gregoire Banderet wrote:
> Hello,
>
> I use the libxml2 in my multi-threaded app (let's say MYAPP).
> MYAPP runs on Linux-ppc and links libxml2 statically (libxml2.a).
> MYAPP is able to load plugins, and one of these plugins uses libxml2 
> too. This plugin also links statically libxml2.

  Never ever move tree strcutures between both, it will crash !

> My question: Should I call xmlInitParser() and xmlCleanupParser() in the 
> plugin code?

  xmlInitParser() yes, xmlCleanupParser() never, you don't care about a 
few KBytes left per lib.

> The doc says that xmlInitParser() should be called once per process, so 
> the answer should be "no".

  usually there is one instance of the library per process hence the guideline.

> But as the code of libxml2 is duplicated in the plugin (because of 
> static link), will all the libxml2 variables initialized?
  of course not. How could the two instances of libxml2 linked statically
be aware of each other, clearly not possible.

> core on pthred_exit. The crash is in xmlFreeGlobalState(). I guess 
> because of the pthread_key_create(&globalkey, xmlFreeGlobalState) done 
> in xmlOnceInit(void).

  Patch your libraries to avoid it. You put yourself in a corner by doing
static dual inclusion. No way the lib can detect or handle that behaviour
since you're static you will need to mainatin a local patch.

> PS: I can't use libxml2 as a shared lib.

  And I can't handle your corner case, sorry ...

Daniel

-- 
Daniel Veillard      | Red Hat http://redhat.com/
veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
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