Windows: Prevent event processing during QDesktopServices::openUrl()

The platform implementation uses the Win32 API ShellExecute(),
which may spin an event loop to do COM processing, causing things
like QMetaCallEvent being processed. Run it in a thread
to suppress this.

Pick-to: 5.15
Fixes: QTBUG-85676
Change-Id: I240ca78b41b39ded22e466662ffce8e9b03c10a2
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

1 files changed, 24 insertions, 4 deletions

diff --git a/src/plugins/platforms/windows/qwindowsservices.cpp b/src/plugins/platforms/windows/qwindowsservices.cpp
index 09ae55cd99..8a95cc53a8 100644
--- a/src/plugins/platforms/windows/qwindowsservices.cpp
+++ b/src/plugins/platforms/windows/qwindowsservices.cpp
@@ -44,6 +44,8 @@
 #include <QtCore/qurl.h>
 #include <QtCore/qdebug.h>
 #include <QtCore/qdir.h>
+#include <QtCore/qscopedpointer.h>
+#include <QtCore/qthread.h>
 
 #include <QtCore/private/qwinregistry_p.h>
 
@@ -54,15 +56,33 @@ QT_BEGIN_NAMESPACE
 
 enum { debug = 0 };
 
+static quintptr runShellExecute(const wchar_t *path)
+{
+    HINSTANCE result = nullptr;
+    if (SUCCEEDED(CoInitializeEx(NULL, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE))) {
+        result = ShellExecute(nullptr, nullptr, path, nullptr, nullptr, SW_SHOWNORMAL);
+        CoUninitialize();
+    }
+    return reinterpret_cast<quintptr>(result);
+}
+
 static inline bool shellExecute(const QUrl &url)
 {
     const QString nativeFilePath = url.isLocalFile() && !url.hasFragment() && !url.hasQuery()
         ? QDir::toNativeSeparators(url.toLocalFile())
         : url.toString(QUrl::FullyEncoded);
-    const auto result =
-        reinterpret_cast<quintptr>(ShellExecute(nullptr, nullptr,
-                                                reinterpret_cast<const wchar_t *>(nativeFilePath.utf16()),
-                                                nullptr, nullptr, SW_SHOWNORMAL));
+
+
+    // Run ShellExecute() in a thread since it may spin the event loop.
+    // Prevent it from interfering with processing of posted events (QTBUG-85676).
+    quintptr result = 0;
+    quintptr *resultPtr = &result;
+    const auto path = reinterpret_cast<const wchar_t *>(nativeFilePath.utf16());
+    QScopedPointer<QThread> thread(QThread::create([path, resultPtr]
+                                                   () { *resultPtr = runShellExecute(path); }));
+    thread->start();
+    thread->wait();
+
     // ShellExecute returns a value greater than 32 if successful
     if (result <= 32) {
         qWarning("ShellExecute '%ls' failed (error %zu).", qUtf16Printable(url.toString()), result);