18.5.4.Server Main Function

The server main function for a customized Virtuoso server has the following format:

static void (*old_ddl_hook) (client_connection_t *cli) = NULL;

static void
ddl_hook (client_connection_t *cli)
  if (old_ddl_hook)
    old_ddl_hook (cli);

  /* DDL code (depending on the server being fully initialized
    (ex: create table) ) goes here */

static void
init_func (void)
  old_ddl_hook = set_ddl_init_hook (ddl_hook);
  /* initialization code (prerequisite for server initialization
     (bif_define, unrelated init code) goes here */

main (int argc, char *argv[])
  VirtuosoServerSetInitHook (init_func);
  return VirtuosoServerMain (argc, argv);

There are three phases to custom code initialization:

execution of the main() function
execution of the init_func() function
execution of the ddl_hook() function

The init_func() function is called before any server initialization functions are called. This is typically a place for defining new VSEs, allocation of synchronization objects (since the server does not have any threads yet), and/or custom code initialization not related to Virtuoso. Here, the set_ddl_init_hook() should be called also, if it exists, to register the ddl_hook() callback function.

[Note] Note:

The old_ddl_hook() mechanism - this allows queuing of the ddl_hooks.

The ddl_hook() function is called during normal startup just before the roll forward, but after the server's internal structure has been initialized. This is typically a place to execute SQL statements to initialize the extension. The variable client_connection_t * is passed to the function to provide the client connection that should be used for SQL execution.

The main() function can call VirtuosoServerSetInitHook() if there is any Virtuoso-related initialization to be performed, and should then call the VirtuosoServerMain() function to start the Virtuoso server. The VirtuosoServerMain() function will return control after the server has been shut down.