Re: [xml] Per parser xmlGcMemSetup

Hi Joachim,

Joachim Zobel wrote:

I have an apache module that uses libxml2. I have found a (potential, no
reports yet) problem with its usage of xmlGcMemSetup. I need to call
this for my module to work correctly. If there are other modules using
libxml2 (mod_php does) and they call xmlGcMemSetup, one of the modules
will stop working.
PHP does not change the memory handling routines (although this had been a request early on but turned down). Doing so would start screwing around with other modules that use libxml2. I urge you not to do this if your module is for more than just some specific implementation and going to be distributed publicly.
The problem is not threads, the problem is that other parts of apache
may be using libxml2 globals independently.
There is pretty much a gentleman's agreement with the other module developers using libxml2 that I know not to abuse the globals. This allows for all the modules to co-exist peacefully. When problems are identified in other modules, everyone, so far at least, is amenable to altering their code to make sure they all play nice together.

- During module initialization, don't alter globals (as that impacts all other modules and also can be problematic depending upon order of module initialization). For example, I limit my call to xmlInitParser to insure it gets initialized in main thread.

- Try not to use globals. Many functions have been added over the years that allow settings/options to be passed directly eliminating the need to use globals.

- If having to use globals, make sure they do not persists over the request. Any changes to globals should be reset to previous state as soon as possible.
I have just found globals.c, but do not understand it yet. Are there any
examples on how to use this?
The globals are really not that difficult. Here is a small example of disabling empty tags I use when supporting older libxml2 versions (prior to being able to use the XML_SAVE_NO_EMPTY option). Notice that it is reset back to original value right after use.
/* get curent setting and then set to 1 */
int saveempty = xmlSaveNoEmptyTags;
xmlSaveNoEmptyTags = 1;

... /* your code here */

/* reset global to previous value */
xmlSaveNoEmptyTags = saveempty;


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