3 files changed, 42 insertions, 15 deletions

diff --git a/src/corelib/kernel/qobjectdefs.h b/src/corelib/kernel/qobjectdefs.h
index 28674193c3..418b8cf1d2 100644
--- a/src/corelib/kernel/qobjectdefs.h
+++ b/src/corelib/kernel/qobjectdefs.h
@@ -576,6 +576,7 @@ struct Q_CORE_EXPORT QMetaObject
 
 private:
     static bool invokeMethodImpl(QObject *object, QtPrivate::QSlotObjectBase *slot, Qt::ConnectionType type, void *ret);
+    friend class QTimer;
 };
 
 class Q_CORE_EXPORT QMetaObject::Connection {
diff --git a/src/corelib/kernel/qtimer.cpp b/src/corelib/kernel/qtimer.cpp
index 13f027074a..188d529f04 100644
--- a/src/corelib/kernel/qtimer.cpp
+++ b/src/corelib/kernel/qtimer.cpp
@@ -42,6 +42,8 @@
 #include "qabstracteventdispatcher.h"
 #include "qcoreapplication.h"
 #include "qobject_p.h"
+#include "qthread.h"
+#include "qcoreapplication_p.h"
 
 QT_BEGIN_NAMESPACE
 
@@ -343,6 +345,33 @@ void QTimer::singleShotImpl(int msec, Qt::TimerType timerType,
                             const QObject *receiver,
                             QtPrivate::QSlotObjectBase *slotObj)
 {
+    if (msec == 0) {
+        bool deleteReceiver = false;
+        // Optimize: set a receiver context when none is given, such that we can use
+        // QMetaObject::invokeMethod which is more efficient than going through a timer.
+        // We need a QObject living in the current thread. But the QThread itself lives
+        // in a different thread - with the exception of the main QThread which lives in
+        // itself. And QThread::currentThread() is among the few QObjects we know that will
+        // most certainly be there. Note that one can actually call singleShot before the
+        // QApplication is created!
+        if (!receiver && QThread::currentThread() == QCoreApplicationPrivate::mainThread()) {
+            // reuse main thread as context object
+            receiver = QThread::currentThread();
+        } else if (!receiver) {
+            // Create a receiver context object on-demand. According to the benchmarks,
+            // this is still more efficient than going through a timer.
+            receiver = new QObject;
+            deleteReceiver = true;
+        }
+
+        QMetaObject::invokeMethodImpl(const_cast<QObject *>(receiver), slotObj,
+                                      Qt::QueuedConnection, nullptr);
+
+        if (deleteReceiver)
+            const_cast<QObject *>(receiver)->deleteLater();
+        return;
+    }
+
     new QSingleShotTimer(msec, timerType, receiver, slotObj);
 }
 
diff --git a/src/testlib/qtest.h b/src/testlib/qtest.h
index ebd94939ce..89abc616d9 100644
--- a/src/testlib/qtest.h
+++ b/src/testlib/qtest.h
@@ -424,48 +424,45 @@ int main(int argc, char *argv[]) \
 #  define QTEST_DISABLE_KEYPAD_NAVIGATION
 #endif
 
-#define QTEST_MAIN(TestObject) \
-int main(int argc, char *argv[]) \
-{ \
+#define QTEST_MAIN_IMPL(TestObject) \
     TESTLIB_SELFCOVERAGE_START(#TestObject) \
     QApplication app(argc, argv); \
     app.setAttribute(Qt::AA_Use96Dpi, true); \
     QTEST_DISABLE_KEYPAD_NAVIGATION \
     TestObject tc; \
     QTEST_SET_MAIN_SOURCE_PATH \
-    return QTest::qExec(&tc, argc, argv); \
-}
+    return QTest::qExec(&tc, argc, argv);
 
 #elif defined(QT_GUI_LIB)
 
 #include <QtTest/qtest_gui.h>
 
-#define QTEST_MAIN(TestObject) \
-int main(int argc, char *argv[]) \
-{ \
+#define QTEST_MAIN_IMPL(TestObject) \
     TESTLIB_SELFCOVERAGE_START(#TestObject) \
     QGuiApplication app(argc, argv); \
     app.setAttribute(Qt::AA_Use96Dpi, true); \
     TestObject tc; \
     QTEST_SET_MAIN_SOURCE_PATH \
-    return QTest::qExec(&tc, argc, argv); \
-}
+    return QTest::qExec(&tc, argc, argv);
 
 #else
 
-#define QTEST_MAIN(TestObject) \
-int main(int argc, char *argv[]) \
-{ \
+#define QTEST_MAIN_IMPL(TestObject) \
     TESTLIB_SELFCOVERAGE_START(#TestObject) \
     QCoreApplication app(argc, argv); \
     app.setAttribute(Qt::AA_Use96Dpi, true); \
     TestObject tc; \
     QTEST_SET_MAIN_SOURCE_PATH \
-    return QTest::qExec(&tc, argc, argv); \
-}
+    return QTest::qExec(&tc, argc, argv);
 
 #endif // QT_GUI_LIB
 
+#define QTEST_MAIN(TestObject) \
+int main(int argc, char *argv[]) \
+{ \
+    QTEST_MAIN_IMPL(TestObject) \
+}
+
 #define QTEST_GUILESS_MAIN(TestObject) \
 int main(int argc, char *argv[]) \
 { \