Improve performance of QTimer::singleShot

Avoid allocation of QObject and OS timer.

Reviewed-by: Olivier Goffart

2 files changed, 25 insertions, 1 deletions

diff --git a/src/corelib/kernel/qtimer.cpp b/src/corelib/kernel/qtimer.cpp
index e17c995..7650f6a 100644
--- a/src/corelib/kernel/qtimer.cpp
+++ b/src/corelib/kernel/qtimer.cpp
@@ -339,8 +339,20 @@ QT_END_INCLUDE_NAMESPACE
 
 void QTimer::singleShot(int msec, QObject *receiver, const char *member)
 {
-    if (receiver && member)
+    if (receiver && member) {
+        if (msec == 0) {
+            // special code shortpath for 0-timers
+            const char* bracketPosition = strchr(member, '(');
+            if (!bracketPosition || !(member[0] >= '0' && member[0] <= '3')) {
+                qWarning("QTimer::singleShot: Invalid slot specification");
+                return;
+            }
+            QByteArray methodName(member+1, bracketPosition - 1 - member); // extract method name
+            QMetaObject::invokeMethod(receiver, methodName.constData(), Qt::QueuedConnection);
+            return;
+        }
         (void) new QSingleShotTimer(msec, receiver, member);
+    }
 }
 
 /*!
diff --git a/tests/auto/qtimer/tst_qtimer.cpp b/tests/auto/qtimer/tst_qtimer.cpp
index cc97e4e..a0408ef 100644
--- a/tests/auto/qtimer/tst_qtimer.cpp
+++ b/tests/auto/qtimer/tst_qtimer.cpp
@@ -85,6 +85,7 @@ private slots:
     void timerFiresOnlyOncePerProcessEvents();
     void timerIdPersistsAfterThreadExit();
     void cancelLongTimer();
+    void singleShotStaticFunctionZeroTimeout();
 };
 
 class TimerHelper : public QObject
@@ -611,5 +612,16 @@ void tst_QTimer::cancelLongTimer()
     QVERIFY(!timer.isActive());
 }
 
+void tst_QTimer::singleShotStaticFunctionZeroTimeout()
+{
+    TimerHelper helper;
+
+    QTimer::singleShot(0, &helper, SLOT(timeout()));
+    QTest::qWait(500);
+    QCOMPARE(helper.count, 1);
+    QTest::qWait(500);
+    QCOMPARE(helper.count, 1);
+}
+
 QTEST_MAIN(tst_QTimer)
 #include "tst_qtimer.moc"