winrt: Explicitly set main thread in QCoreApplication's constructor

For winrt we cannot rely on the fact, that QThread::current will be called
from the correct thread for the first time. The application's main entry
point creates a suspended thread and starts it right afterwards. At that
moment, other functionality (QLoggingRegistry for example) might have
called QThread::current, which set the wrong thread as the main thread. In
order to avoid this situation, the main thread is explicitly set in
QCoreApplication's constructor.

Task-number: QTBUG-66418
Change-Id: I8b6347357a80eb395ae758bd3d420adef0826751
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

3 files changed, 40 insertions, 2 deletions

diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index 1350a7aa94..463e30e1c3 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -482,6 +482,10 @@ QCoreApplicationPrivate::QCoreApplicationPrivate(int &aargc, char **aargv, uint
         qFatal("FATAL: The application binary appears to be running setuid, this is a security hole.");
 #  endif // Q_OS_UNIX
 
+#ifdef Q_OS_WINRT
+    QThreadData::setMainThread();
+#endif
+
     QThread *cur = QThread::currentThread(); // note: this may end up setting theMainThread!
     if (cur != theMainThread)
         qWarning("WARNING: QApplication was not created in the main() thread.");
diff --git a/src/corelib/thread/qthread_p.h b/src/corelib/thread/qthread_p.h
index 64e3f33191..7d9442ab79 100644
--- a/src/corelib/thread/qthread_p.h
+++ b/src/corelib/thread/qthread_p.h
@@ -243,6 +243,9 @@ public:
     ~QThreadData();
 
     static Q_AUTOTEST_EXPORT QThreadData *current(bool createIfNecessary = true);
+#ifdef Q_OS_WINRT
+    static void setMainThread();
+#endif
     static void clearCurrentThreadData();
     static QThreadData *get2(QThread *thread)
     { Q_ASSERT_X(thread != 0, "QThread", "internal error"); return thread->d_func()->data; }
diff --git a/src/corelib/thread/qthread_win.cpp b/src/corelib/thread/qthread_win.cpp
index eebaf90d9b..e04d27d7b6 100644
--- a/src/corelib/thread/qthread_win.cpp
+++ b/src/corelib/thread/qthread_win.cpp
@@ -140,11 +140,15 @@ QThreadData *QThreadData::current(bool createIfNecessary)
         threadData->isAdopted = true;
         threadData->threadId.store(reinterpret_cast<Qt::HANDLE>(quintptr(GetCurrentThreadId())));
 
+#ifndef Q_OS_WINRT
         if (!QCoreApplicationPrivate::theMainThread) {
             QCoreApplicationPrivate::theMainThread = threadData->thread.load();
-            // TODO: is there a way to reflect the branch's behavior using
-            // WinRT API?
         } else {
+#else
+        // for winrt the main thread is set explicitly in QCoreApplication's constructor as the
+        // native main thread (Xaml thread) is not Qt's main thread.
+        {
+#endif
             HANDLE realHandle = INVALID_HANDLE_VALUE;
             DuplicateHandle(GetCurrentProcess(),
                     GetCurrentThread(),
@@ -159,6 +163,33 @@ QThreadData *QThreadData::current(bool createIfNecessary)
     return threadData;
 }
 
+#ifdef Q_OS_WINRT
+void QThreadData::setMainThread()
+{
+    Q_ASSERT(!QCoreApplicationPrivate::theMainThread);
+    qt_create_tls();
+    QThreadData *threadData = reinterpret_cast<QThreadData *>(TlsGetValue(qt_current_thread_data_tls_index));
+    if (!threadData) {
+        threadData = new QThreadData;
+        // This needs to be called prior to new AdoptedThread() to
+        // avoid recursion.
+        TlsSetValue(qt_current_thread_data_tls_index, threadData);
+        QT_TRY {
+            threadData->thread = new QAdoptedThread(threadData);
+        } QT_CATCH(...) {
+            TlsSetValue(qt_current_thread_data_tls_index, 0);
+            threadData->deref();
+            threadData = 0;
+            QT_RETHROW;
+        }
+        threadData->deref();
+        threadData->isAdopted = true;
+        threadData->threadId.store(reinterpret_cast<Qt::HANDLE>(quintptr(GetCurrentThreadId())));
+    }
+    QCoreApplicationPrivate::theMainThread = threadData->thread.load();
+}
+#endif
+
 void QAdoptedThread::init()
 {
     d_func()->handle = GetCurrentThread();