Adjust the loading order of preload (#1027)

Prioritize loading the process_shared_preload_libraries.h
header file, and then load the shared_preload_libraries from
postgresql.conf.

Author: MisterRaindrop

src/backend/utils/init/miscinit.c

@@ -1764,40 +1764,41 @@ static char*
 expand_shared_preload_libraries_string()
 {
 	List	   *elemlist = NIL;
+	List	   *pg_elemlist = NIL;
 	List	   *deduplicate_elemlist = NIL;
 	ListCell   *l;
 	char	   *rawstring;
 	char	   *libraries = shared_preload_libraries_string;
 
+	/* load process_shared_preload_libraries.h libraries */
+	int shared_preload_libraries_num = sizeof(process_shared_preload_libraries_array) / sizeof(char *);
+	if (shared_preload_libraries_num > 0)
+	{
+		for (int i = 0; i < shared_preload_libraries_num; i++)
+		{
+			elemlist = lappend(elemlist, pstrdup((char*)process_shared_preload_libraries_array[i]));
+		}
+	}
+
 	/* Need a modifiable copy of string */
 	rawstring = pstrdup(libraries);
 	if (libraries != NULL && libraries[0] != '\0')
 	{
 		/* Parse string into list of filename paths */
-		if (!SplitDirectoriesString(rawstring, ',', &elemlist))
+		if (!SplitDirectoriesString(rawstring, ',', &pg_elemlist))
 		{
 			/* syntax error in list */
-			list_free_deep(elemlist);
+			list_free_deep(pg_elemlist);
 			pfree(rawstring);
 			ereport(LOG,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 					errmsg("invalid list syntax in parameter \"%s\"",
 							libraries)));
 			return NULL;
 		}
-
 	}
 
-	/* load expand libraries */
-	int shared_preload_libraries_num = sizeof(process_shared_preload_libraries_array) / sizeof(char *);
-	if (shared_preload_libraries_num > 0)
-	{
-		for (int i = 0; i < shared_preload_libraries_num; i++)
-		{
-			elemlist = lappend(elemlist, pstrdup((char*)process_shared_preload_libraries_array[i]));
-		}
-
-	}
+	elemlist = list_concat(elemlist, pg_elemlist);
 
 	if (list_length(elemlist) == 0)
 	{
@@ -1806,7 +1807,6 @@ expand_shared_preload_libraries_string()
 		return NULL;
 	}
 
-
 	/* deduplicate list string */
 	deduplicate_elemlist = removeDuplicates(elemlist);