Use of static var in MapScript mapObj.nextLabel

[Daniel Morissette]

While working on the implementation of label priority, I noticed that 
the mapObj.nextLabel() method uses a static variable to iterate over 
labels. This is not safe for multi-thread environments, and does not 
allow using the function more than once per instance of label cache.

The same code is present in mapscript/swiginc/map.i and in 
mapscript/php3/mapscript_i.c

   labelCacheMemberObj *nextLabel() {
     static int i=0;

     if(i<self->labelcache.numlabels)
       return &(self->labelcache.labels[i++]);
     else
       return NULL;	
   }

What do we want to do to fix it?

The simplest option would be to store the last_label_read as a member of 
mapObj (or of labelCacheObj) and then add a rewindLabelCache() method or 
something like that to reset the iterator.

Whatever we decide, I will for sure move this code down to the C core in 
msGetNextLabel() and msRewindLabelCache() functions to avoid having it 
in two places.

Any preferences on the fix?

FYI I have filed ticket 2133 about this:
https://trac.osgeo.org/mapserver/ticket/2133

Daniel
-- 
Daniel Morissette
http://www.mapgears.com/