bug 839341 100% CPU usage with ST_UNION in maria-5.3-gis.

    Line loops weren't recognized when collect results.
    Fixed by checking if we got the same beginning point of the line.

per-file comments:
  mysql-test/r/gis-precise.result
bug 839341 100% CPU usage with ST_UNION in maria-5.3-gis.
      test result updated.
  mysql-test/t/gis-precise.test
bug 839341 100% CPU usage with ST_UNION in maria-5.3-gis.
      test case added.
  sql/gcalc_tools.cc
bug 839341 100% CPU usage with ST_UNION in maria-5.3-gis.
      check if we get the beginning node of the linestring, then cut the loop.

mysql-test/r/gis-precise.result

@@ -320,3 +320,6 @@ POLYGON((2 0,2 5,3 3,3 2,7 5,2 0))
 SELECT AsText(ST_INTERSECTION(LinestringFromText('LINESTRING(1 1, 2 2)'), GeometryFromText('LINESTRING(3 3, 4 4)')));
 AsText(ST_INTERSECTION(LinestringFromText('LINESTRING(1 1, 2 2)'), GeometryFromText('LINESTRING(3 3, 4 4)')))
 GEOMETRYCOLLECTION()
+SELECT AsText(ST_UNION(GEOMETRYFROMTEXT('POINT(8 1)') ,MULTILINESTRINGFROMTEXT('MULTILINESTRING((3 5, 2 5, 2 4, 3 4, 3 5))')));
+AsText(ST_UNION(GEOMETRYFROMTEXT('POINT(8 1)') ,MULTILINESTRINGFROMTEXT('MULTILINESTRING((3 5, 2 5, 2 4, 3 4, 3 5))')))
+GEOMETRYCOLLECTION(POINT(8 1),LINESTRING(2 4,2 5,3 5,3 4,2 4))

mysql-test/t/gis-precise.test

@@ -204,3 +204,5 @@ SELECT AsText( ST_UNION(
 
 SELECT AsText(ST_INTERSECTION(LinestringFromText('LINESTRING(1 1, 2 2)'), GeometryFromText('LINESTRING(3 3, 4 4)')));
 
+#bug 839341 100% CPU usage with ST_UNION in maria-5.3-gis
+SELECT AsText(ST_UNION(GEOMETRYFROMTEXT('POINT(8 1)') ,MULTILINESTRINGFROMTEXT('MULTILINESTRING((3 5, 2 5, 2 4, 3 4, 3 5))')));

sql/gcalc_tools.cc

@@ -1158,6 +1158,7 @@ int Gcalc_operation_reducer::get_line_result(res_point *cur,
                                              Gcalc_result_receiver *storage)
 {
   res_point *next;
+  res_point *cur_orig= cur;
   int move_upward= 1;
   if (cur->glue)
   {
@@ -1171,6 +1172,14 @@ int Gcalc_operation_reducer::get_line_result(res_point *cur,
       if (!next)
       {
 	next= cur->glue;
+        if (next == cur_orig)
+        {
+          /* It's the line loop */
+          cur= cur_orig;
+          cur->glue->glue= NULL;
+          move_upward= 1;
+          break;
+        }
 	move_upward^= 1;
       }
     }