C examples for single-threaded Sessions API v2 proposal

run_in_transaction.c

bool
user_func (mongoc_client_session_t *session,
           void *data,
           bson_t *reply /* OUT */,
           bson_error_t *error /* OUT */)
{
   /* the void pointer is used to pass any user data */
   user_defined_t *user_data = (user_defined_t *) data;

   /* this is just another reference to the same client defined in main(),
    * nothing special here except convenience */
   mongoc_client_t *client = mongoc_client_session_get_client (session);
   mongoc_collection_t *c = mongoc_client_get_collection (client, "db", "coll");
   bson_t doc = BSON_INITIALIZER;
   bson_t opts = BSON_INITIALIZER;
   bool r;

   /* must explicitly pass session in function's opts */
   mongoc_client_session_append (session, &opts);
   r = mongoc_collection_insert_one (c, &doc, &opts, reply, error);

   bson_destroy (&opts);

   /* with_transaction knows from the return value and from the reply contents
    * whether this failed and whether to retry the txn */
   return r;
}

int
main ()
{
   mongoc_client_t *client = mongoc_client_new (NULL);
   mongoc_client_session_t *session = mongoc_client_start_session (
      client, NULL /* options */);

   bson_error_t error;
   bson_t reply;
   bool r;

   /* some optional data if the application desires */
   user_defined_t user_data;

   /* with_transaction can retry user_func if it fails with a transient txn
    * error, or else aborts the transaction and returns false. it commits, with
    * proper retry logic, if user_func succeeds */
   r = mongoc_client_session_with_transaction (session,
                                               user_func,
                                               &user_data,
                                               &reply,
                                               &error);

   if (!r) {
      fprintf (stderr, "uh-oh!: %s\n", error.message);
      return 1;
   }

   return 0;
}