don't reparse the same mapfile over and over again for fastcgi

[tbonfort]

the given map= mapfile parameter is parsed at each request in the fastcgi mapserv.c

we can squeeze a bit more performance out if we can keep the parsed mapfile in memory, and use a copy of it instead of reparsing it at each request.

The following points should be taken into account when implementing:

• the behavior should only be active for fastcgi requests
• a user should be able to disable this for a given mapfile by setting a CONFIG option or an environment variable
• the original mapfile's modification time should be checked to see if the in-memory copy is stale or not

[tbonfort]

initial patch for mapserv.c:

mapserv.c

@@ -185 +185 @@
 {
   int i;
   mapObj *map = NULL;
+  static char *lastmapname = NULL;
+  static mapObj *lastmap = NULL;
 
   for(i=0;i<mapserv->request->NumParams;i++) /* find the mapfile parameter first */
     if(strcasecmp(mapserv->request->ParamNames[i], "map") == 0) break;
@@ -212 +214 @@
       }
 
       /* ok to try to load now */
-      map = msLoadMap(mapserv->request->ParamValues[i], NULL);
+      if(!lastmapname || strcmp(lastmapname,mapserv->request->ParamValues[i])) {
+         if(lastmap)
+            msFreeMap(lastmap);
+         lastmap = msLoadMap(mapserv->request->ParamValues[i], NULL);
+         if(lastmapname) free(lastmapname);
+         lastmapname = strdup(mapserv->request->ParamValues[i]);
+      }
+      map = msNewMapObj();
+      msCopyMap(map,lastmap);
     }
   }

[tbonfort]

initial implementation in r13105