Never call QtWebEngine::initialize from DllMain

On windows, calling QtWebEngine::initialize from DllMain may crash,
depending on what QPA backend is used.

We make sure to only add a qAddPreRoutine initializing QtWebEngine
if there is no instance of QCoreApplication.
By doing so, we support linking to QtWebEngineWidget from a plugin,
while still initializing the WebEngine automatically when linked to
the main application binary.

Task-number: QTBUG-46720
Reviewed-by: Jocelyn Turcotte (Woboq GmbH) <jturcotte@woboq.com>
(cherry picked from commit 6a8d99ab00ace2084820547572dc05ac8ad2bc5a)
Change-Id: Id3b2c1e21e01808cef124f8ece6b247b1ba613cb
Reviewed-by: Michael Brüning <michael.bruning@theqtcompany.com>

2 files changed, 16 insertions, 6 deletions

diff --git a/src/core/api/qtwebenginecoreglobal.cpp b/src/core/api/qtwebenginecoreglobal.cpp
index 0e857d7d9..e60e6139e 100644
--- a/src/core/api/qtwebenginecoreglobal.cpp
+++ b/src/core/api/qtwebenginecoreglobal.cpp
@@ -75,6 +75,11 @@ QWEBENGINE_PRIVATE_EXPORT void initialize()
         qFatal("QtWebEngine::initialize() must be called after the construction of the application object.");
         return;
     }
+
+    // Bail out silently if the user did not construct a QGuiApplication.
+    if (!qobject_cast<QGuiApplication *>(app))
+        return;
+
     if (app->thread() != QThread::currentThread()) {
         qFatal("QtWebEngine::initialize() must be called from the Qt gui thread.");
         return;
diff --git a/src/webenginewidgets/api/qtwebenginewidgetsglobal.cpp b/src/webenginewidgets/api/qtwebenginewidgetsglobal.cpp
index 263376e45..5ebb8b546 100644
--- a/src/webenginewidgets/api/qtwebenginewidgetsglobal.cpp
+++ b/src/webenginewidgets/api/qtwebenginewidgetsglobal.cpp
@@ -36,7 +36,7 @@
 
 #include "qtwebenginewidgetsglobal.h"
 
-#include <QGuiApplication>
+#include <QCoreApplication>
 
 namespace QtWebEngineCore
 {
@@ -46,13 +46,18 @@ namespace QtWebEngineCore
 QT_BEGIN_NAMESPACE
 static void initialize()
 {
-    // Bail out silently if the user did not construct a QGuiApplication.
-    if (!qobject_cast<QGuiApplication *>(QCoreApplication::instance()))
+    //On window/ANGLE, calling QtWebEngine::initialize from DllMain will result in a crash.
+    //To ensure it doesn't, we check that when loading the library
+    //QCoreApplication is not yet instantiated, ensuring the call will be deferred
+#if defined(Q_OS_WIN)
+    if (QCoreApplication::instance()
+            && QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGLES) {
         return;
-
-    QtWebEngineCore::initialize();
+    }
+#endif
+    qAddPreRoutine(QtWebEngineCore::initialize);
 }
 
-Q_COREAPP_STARTUP_FUNCTION(initialize)
+Q_CONSTRUCTOR_FUNCTION(initialize)
 
 QT_END_NAMESPACE