c++ - sfml 2.3 pollEvent pauses execution -

int main() {      sf::renderwindow window;     window.create(sf::videomode(800,600), "game");      window.setverticalsyncenabled(true);      sf::circleshape shape(100.f,5);     shape.setfillcolor(sf::color::green);      shape.setposition(400,300);       while (window.isopen())     {         if (sf::keyboard::iskeypressed(sf::keyboard::up))         {             shape.move(0,-5);         }          sf::event event;         while (window.pollevent(event))         {             switch(event.type)             {                 case sf::event::closed:                     window.close();                     break;                  default:                     break;             }         }           window.clear();         window.draw(shape);         window.display();      } } 

i'm running debian 8 , trying make things using c++ , sfml. whenever have pollevent loop, while(window.isopen()) loop waits event, therefore entire thing unusable. aware there similar questions mine, none of solutions work me.