Avoid using qGuiApp in QOpenGLVao::destroy()

There are convoluted cases, based on the backtrace attached
to the associated bug report, where we attempt to destroy a
QOpenGLVertexArrayObject during the destruction of Q(Gui)Application.

Just avoid accessing qGuiApp in destroy(). Rather, store it in create().

Fixes: QTBUG-75138
Pick-to: 5.15
Change-Id: If8e67301c0843cbf3a409dcf427f44c42079de2f
Reviewed-by: Christian Strømme <christian.stromme@qt.io>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/opengl/qopenglvertexarrayobject.cpp b/src/opengl/qopenglvertexarrayobject.cpp
index 9c85d73c22..7f28a0bc61 100644
--- a/src/opengl/qopenglvertexarrayobject.cpp
+++ b/src/opengl/qopenglvertexarrayobject.cpp
@@ -103,6 +103,7 @@ public:
         : vao(0)
         , vaoFuncsType(NotSupported)
         , context(nullptr)
+        , guiThread(nullptr)
     {
     }
 
@@ -137,6 +138,7 @@ public:
     } vaoFuncsType;
 
     QOpenGLContext *context;
+    QThread *guiThread;
 };
 
 bool QOpenGLVertexArrayObjectPrivate::create()
@@ -161,6 +163,8 @@ bool QOpenGLVertexArrayObjectPrivate::create()
     context = ctx;
     QObject::connect(context, SIGNAL(aboutToBeDestroyed()), q, SLOT(_q_contextAboutToBeDestroyed()));
 
+    guiThread = qGuiApp->thread();
+
     if (ctx->isOpenGLES()) {
         if (ctx->format().majorVersion() >= 3 || ctx->hasExtension(QByteArrayLiteral("GL_OES_vertex_array_object"))) {
             vaoFuncs.helper = new QOpenGLVertexArrayObjectHelper(ctx);
@@ -210,7 +214,7 @@ void QOpenGLVertexArrayObjectPrivate::destroy()
         // Before going through the effort of creating an offscreen surface
         // check that we are on the GUI thread because otherwise many platforms
         // will not able to create that offscreen surface.
-        if (QThread::currentThread() != qGuiApp->thread()) {
+        if (QThread::currentThread() != guiThread) {
             ctx = nullptr;
         } else {
             // Cannot just make the current surface current again with another context.