rb_setselect_poll(F, RB_SELECT_READ, NULL, NULL);
if(F->write_handler == NULL)
rb_setselect_poll(F, RB_SELECT_WRITE, NULL, NULL);
rb_setselect_poll(F, RB_SELECT_READ, NULL, NULL);
if(F->write_handler == NULL)
rb_setselect_poll(F, RB_SELECT_WRITE, NULL, NULL);