#2382, Can't upgrade postgis ERROR: attempt to redefine parameter "postgis.backend"

git-svn-id: http://svn.osgeo.org/postgis/trunk@12350 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/postgis/lwgeom_backend_api.c b/postgis/lwgeom_backend_api.c
index 0910ad0e4033a32293375134852c07bcf6d137b3..78de8738fd996c9226f0c7e4edcd22e47e68c56e 100644 (file)
--- a/postgis/lwgeom_backend_api.c
+++ b/postgis/lwgeom_backend_api.c
@@ -18,6 +18,7 @@
 
 /* for custom variables */
 #include "utils/guc.h"
+#include "utils/guc_tables.h"
 
 #include "../postgis_config.h"
 #include "lwgeom_backend_api.h"
@@ -96,7 +97,35 @@ static void lwgeom_backend_switch( const char* newvalue, void* extra )
 
 void lwgeom_init_backend()
 {
-    DefineCustomStringVariable( "postgis.backend", /* name */
+       static const char *guc_name = "postgis.backend";
+
+       /* #2382 Before trying to create a user GUC, make sure */
+       /* that the name is not already in use. Why would it be in use? */
+       /* During an upgrade, a prior copy of the PostGIS library will */
+       /* already be loaded in memory and the GUC already defined. We */
+       /* can skip GUC definition in this case, so we just return. */
+
+    struct config_generic **guc_vars;
+    int                     numOpts,
+                            i;
+       guc_vars = get_guc_variables();
+    numOpts = GetNumConfigOptions();
+
+       /* Uh oh, no GUCs? */
+       if ( ! guc_vars ) return;
+
+       for (i = 0; i < numOpts; i++)
+       {
+               if ( guc_vars[i] && guc_vars[i]->name && strcmp(guc_vars[i]->name, guc_name) == 0 )
+               {
+                       /* Uh oh, this GUC name already exists */
+                       return;
+               }
+       }
+
+       /* Good, the GUC name is not already in use, so this must be a fresh */
+       /* and clean new load of the library, and we can define the user GUC */
+    DefineCustomStringVariable( guc_name, /* name */
                                "Sets the PostGIS Geometry Backend.", /* short_desc */
                                "Sets the PostGIS Geometry Backend (allowed values are 'geos' or 'sfcgal')", /* long_desc */
                                &lwgeom_backend_name, /* valueAddr */