The wiki page doesn't currently reflect that, but if you're passing PGSQL_CONNECT_ASYNC to pg_connect, creating the connection won't block and transitions through extra states expressed by those constants.
PGSQL_CONNECTION_AUTH_OK
PGSQL_CONNECTION_AWAITING_RESPONSE
PGSQL_CONNECTION_MADE
PGSQL_CONNECTION_SETENV
PGSQL_CONNECTION_SSL_STARTUP
PGSQL_CONNECTION_STARTED