I found some examples using makeCurrent and doneCurrent in pairs, such as in Qt example of "X:\Qt\Examples\Qt-5.12.2\opengl\qopenglwidget\glwdiget.cpp", they are called in GLWidget::~GLWidget().
So, Must makeCurrent and doneCurrent that come from QOpenGLWidget be used in pairs? if not what happen? crash? QOpenGLContext is null?