Qt threadred QOpenGLWidget crash

官方QT OpenGL示例有一个错误，当您经常调整Threaded QOpenGLWidget example top level的窗口大小时（拖动窗口），它将崩溃，产生Cannot make QOpenGLContext current in a different thread。我尝试了QT 5.7和QT 5.8。它们都包含相同的问题。

可以找到示例： QtQt5.8.0ExamplesQt-5.8openglthreadedqopenglwidget

这是代码：

glwidget.h

#ifndef GLWIDGET_H
#define GLWIDGET_H
#include <QOpenGLWidget>
#include <QOpenGLFunctions>
#include <QOpenGLShaderProgram>
#include <QOpenGLBuffer>
#include <QVector3D>
#include <QMatrix4x4>
#include <QThread>
#include <QMutex>
#include <QWaitCondition>
#include <QElapsedTimer>
class GLWidget;
class Renderer : public QObject, protected QOpenGLFunctions
{
    Q_OBJECT
public:
    Renderer(GLWidget *w);
    void lockRenderer() { m_renderMutex.lock(); }
    void unlockRenderer() { m_renderMutex.unlock(); }
    QMutex *grabMutex() { return &m_grabMutex; }
    QWaitCondition *grabCond() { return &m_grabCond; }
    void prepareExit() { m_exiting = true; m_grabCond.wakeAll(); }
signals:
    void contextWanted();
public slots:
    void render();
private:
    void paintQtLogo();
    void createGeometry();
    void quad(qreal x1, qreal y1, qreal x2, qreal y2, qreal x3, qreal y3, qreal x4, qreal y4);
    void extrude(qreal x1, qreal y1, qreal x2, qreal y2);
    bool m_inited;
    qreal m_fAngle;
    qreal m_fScale;
    QVector<QVector3D> vertices;
    QVector<QVector3D> normals;
    QOpenGLShaderProgram program;
    QOpenGLBuffer vbo;
    int vertexAttr;
    int normalAttr;
    int matrixUniform;
    GLWidget *m_glwidget;
    QMutex m_renderMutex;
    QElapsedTimer m_elapsed;
    QMutex m_grabMutex;
    QWaitCondition m_grabCond;
    bool m_exiting;
};
class GLWidget : public QOpenGLWidget
{
    Q_OBJECT
public:
    explicit GLWidget(QWidget *parent = 0);
    ~GLWidget();
protected:
    void paintEvent(QPaintEvent *) override { }
signals:
    void renderRequested();
public slots:
    void grabContext();
private slots:
    void onAboutToCompose();
    void onFrameSwapped();
    void onAboutToResize();
    void onResized();
private:
    QThread *m_thread;
    Renderer *m_renderer;
};
#endif

glwidget.cpp

#include "glwidget.h"
#include <math.h>
#include <QGuiApplication>
GLWidget::GLWidget(QWidget *parent)
    : QOpenGLWidget(parent)
{
    setMinimumSize(300, 250);
    connect(this, &QOpenGLWidget::aboutToCompose, this, &GLWidget::onAboutToCompose);
    connect(this, &QOpenGLWidget::frameSwapped, this, &GLWidget::onFrameSwapped);
    connect(this, &QOpenGLWidget::aboutToResize, this, &GLWidget::onAboutToResize);
    connect(this, &QOpenGLWidget::resized, this, &GLWidget::onResized);
    m_thread = new QThread;
    m_renderer = new Renderer(this);
    m_renderer->moveToThread(m_thread);
    connect(m_thread, &QThread::finished, m_renderer, &QObject::deleteLater);
    connect(this, &GLWidget::renderRequested, m_renderer, &Renderer::render);
    connect(m_renderer, &Renderer::contextWanted, this, &GLWidget::grabContext);
    m_thread->start();
}
GLWidget::~GLWidget()
{
    m_renderer->prepareExit();
    m_thread->quit();
    m_thread->wait();
    delete m_thread;
}
void GLWidget::onAboutToCompose()
{
    // We are on the gui thread here. Composition is about to
    // begin. Wait until the render thread finishes.
    m_renderer->lockRenderer();
}
void GLWidget::onFrameSwapped()
{
    m_renderer->unlockRenderer();
    // Assuming a blocking swap, our animation is driven purely by the
    // vsync in this example.
    emit renderRequested();
}
void GLWidget::onAboutToResize()
{
    m_renderer->lockRenderer();
}
void GLWidget::onResized()
{
    m_renderer->unlockRenderer();
}
void GLWidget::grabContext()
{
    m_renderer->lockRenderer();
    QMutexLocker lock(m_renderer->grabMutex());
    context()->moveToThread(m_thread);
    m_renderer->grabCond()->wakeAll();
    m_renderer->unlockRenderer();
}
Renderer::Renderer(GLWidget *w)
    : m_inited(false),
      m_glwidget(w),
      m_exiting(false)
{
}
void Renderer::paintQtLogo()
{
    vbo.bind();
    program.setAttributeBuffer(vertexAttr, GL_FLOAT, 0, 3);
    program.setAttributeBuffer(normalAttr, GL_FLOAT, vertices.count() * 3 * sizeof(GLfloat), 3);
    vbo.release();
    program.enableAttributeArray(vertexAttr);
    program.enableAttributeArray(normalAttr);
    glDrawArrays(GL_TRIANGLES, 0, vertices.size());
    program.disableAttributeArray(normalAttr);
    program.disableAttributeArray(vertexAttr);
}
// Some OpenGL implementations have serious issues with compiling and linking
// shaders on multiple threads concurrently. Avoid this.
Q_GLOBAL_STATIC(QMutex, initMutex)
void Renderer::render()
{
    if (m_exiting)
        return;
    QOpenGLContext *ctx = m_glwidget->context();
    if (!ctx) // QOpenGLWidget not yet initialized
        return;
    // Grab the context.
    m_grabMutex.lock();
    emit contextWanted();
    m_grabCond.wait(&m_grabMutex);
    QMutexLocker lock(&m_renderMutex);
    m_grabMutex.unlock();
    if (m_exiting)
        return;
    Q_ASSERT(ctx->thread() == QThread::currentThread());
    // Make the context (and an offscreen surface) current for this thread. The
    // QOpenGLWidget's fbo is bound in the context.
    m_glwidget->makeCurrent();
    if (!m_inited) {
        m_inited = true;
        initializeOpenGLFunctions();
        QMutexLocker initLock(initMutex());
        QOpenGLShader *vshader = new QOpenGLShader(QOpenGLShader::Vertex, this);
        const char *vsrc =
            "attribute highp vec4 vertex;n"
            "attribute mediump vec3 normal;n"
            "uniform mediump mat4 matrix;n"
            "varying mediump vec4 color;n"
            "void main(void)n"
            "{n"
            "    vec3 toLight = normalize(vec3(0.0, 0.3, 1.0));n"
            "    float angle = max(dot(normal, toLight), 0.0);n"
            "    vec3 col = vec3(0.40, 1.0, 0.0);n"
            "    color = vec4(col * 0.2 + col * 0.8 * angle, 1.0);n"
            "    color = clamp(color, 0.0, 1.0);n"
            "    gl_Position = matrix * vertex;n"
            "}n";
        vshader->compileSourceCode(vsrc);
        QOpenGLShader *fshader = new QOpenGLShader(QOpenGLShader::Fragment, this);
        const char *fsrc =
            "varying mediump vec4 color;n"
            "void main(void)n"
            "{n"
            "    gl_FragColor = color;n"
            "}n";
        fshader->compileSourceCode(fsrc);
        program.addShader(vshader);
        program.addShader(fshader);
        program.link();
        vertexAttr = program.attributeLocation("vertex");
        normalAttr = program.attributeLocation("normal");
        matrixUniform = program.uniformLocation("matrix");
        m_fAngle = 0;
        m_fScale = 1;
        createGeometry();
        vbo.create();
        vbo.bind();
        const int verticesSize = vertices.count() * 3 * sizeof(GLfloat);
        vbo.allocate(verticesSize * 2);
        vbo.write(0, vertices.constData(), verticesSize);
        vbo.write(verticesSize, normals.constData(), verticesSize);
        m_elapsed.start();
    }
    //qDebug("%p elapsed %lld", QThread::currentThread(), m_elapsed.restart());
    glClearColor(0.1f, 0.2f, 0.2f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glFrontFace(GL_CW);
    glCullFace(GL_FRONT);
    glEnable(GL_CULL_FACE);
    glEnable(GL_DEPTH_TEST);
    QMatrix4x4 modelview;
    modelview.rotate(m_fAngle, 0.0f, 1.0f, 0.0f);
    modelview.rotate(m_fAngle, 1.0f, 0.0f, 0.0f);
    modelview.rotate(m_fAngle, 0.0f, 0.0f, 1.0f);
    modelview.scale(m_fScale);
    modelview.translate(0.0f, -0.2f, 0.0f);
    program.bind();
    program.setUniformValue(matrixUniform, modelview);
    paintQtLogo();
    program.release();
    glDisable(GL_DEPTH_TEST);
    glDisable(GL_CULL_FACE);
    m_fAngle += 1.0f;
    // Make no context current on this thread and move the QOpenGLWidget's
    // context back to the gui thread.
    m_glwidget->doneCurrent();
    ctx->moveToThread(qGuiApp->thread());
    // Schedule composition. Note that this will use QueuedConnection, meaning
    // that update() will be invoked on the gui thread.
    QMetaObject::invokeMethod(m_glwidget, "update");
}
void Renderer::createGeometry()
{
    vertices.clear();
    normals.clear();
    qreal x1 = +0.06f;
    qreal y1 = -0.14f;
    qreal x2 = +0.14f;
    qreal y2 = -0.06f;
    qreal x3 = +0.08f;
    qreal y3 = +0.00f;
    qreal x4 = +0.30f;
    qreal y4 = +0.22f;
    quad(x1, y1, x2, y2, y2, x2, y1, x1);
    quad(x3, y3, x4, y4, y4, x4, y3, x3);
    extrude(x1, y1, x2, y2);
    extrude(x2, y2, y2, x2);
    extrude(y2, x2, y1, x1);
    extrude(y1, x1, x1, y1);
    extrude(x3, y3, x4, y4);
    extrude(x4, y4, y4, x4);
    extrude(y4, x4, y3, x3);
    const qreal Pi = 3.14159f;
    const int NumSectors = 100;
    for (int i = 0; i < NumSectors; ++i) {
        qreal angle1 = (i * 2 * Pi) / NumSectors;
        qreal x5 = 0.30 * sin(angle1);
        qreal y5 = 0.30 * cos(angle1);
        qreal x6 = 0.20 * sin(angle1);
        qreal y6 = 0.20 * cos(angle1);
        qreal angle2 = ((i + 1) * 2 * Pi) / NumSectors;
        qreal x7 = 0.20 * sin(angle2);
        qreal y7 = 0.20 * cos(angle2);
        qreal x8 = 0.30 * sin(angle2);
        qreal y8 = 0.30 * cos(angle2);
        quad(x5, y5, x6, y6, x7, y7, x8, y8);
        extrude(x6, y6, x7, y7);
        extrude(x8, y8, x5, y5);
    }
    for (int i = 0;i < vertices.size();i++)
        vertices[i] *= 2.0f;
}
void Renderer::quad(qreal x1, qreal y1, qreal x2, qreal y2, qreal x3, qreal y3, qreal x4, qreal y4)
{
    vertices << QVector3D(x1, y1, -0.05f);
    vertices << QVector3D(x2, y2, -0.05f);
    vertices << QVector3D(x4, y4, -0.05f);
    vertices << QVector3D(x3, y3, -0.05f);
    vertices << QVector3D(x4, y4, -0.05f);
    vertices << QVector3D(x2, y2, -0.05f);
    QVector3D n = QVector3D::normal
        (QVector3D(x2 - x1, y2 - y1, 0.0f), QVector3D(x4 - x1, y4 - y1, 0.0f));
    normals << n;
    normals << n;
    normals << n;
    normals << n;
    normals << n;
    normals << n;
    vertices << QVector3D(x4, y4, 0.05f);
    vertices << QVector3D(x2, y2, 0.05f);
    vertices << QVector3D(x1, y1, 0.05f);
    vertices << QVector3D(x2, y2, 0.05f);
    vertices << QVector3D(x4, y4, 0.05f);
    vertices << QVector3D(x3, y3, 0.05f);
    n = QVector3D::normal
        (QVector3D(x2 - x4, y2 - y4, 0.0f), QVector3D(x1 - x4, y1 - y4, 0.0f));
    normals << n;
    normals << n;
    normals << n;
    normals << n;
    normals << n;
    normals << n;
}
void Renderer::extrude(qreal x1, qreal y1, qreal x2, qreal y2)
{
    vertices << QVector3D(x1, y1, +0.05f);
    vertices << QVector3D(x2, y2, +0.05f);
    vertices << QVector3D(x1, y1, -0.05f);
    vertices << QVector3D(x2, y2, -0.05f);
    vertices << QVector3D(x1, y1, -0.05f);
    vertices << QVector3D(x2, y2, +0.05f);
    QVector3D n = QVector3D::normal
        (QVector3D(x2 - x1, y2 - y1, 0.0f), QVector3D(0.0f, 0.0f, -0.1f));
    normals << n;
    normals << n;
    normals << n;
    normals << n;
    normals << n;
    normals << n;
}

看起来grabContext调用在调整小部件的大小太大大小时无法正确锁定上下文。