Decouple quitOnLastWindowClosed from quitLockEnabled

In a512e210ac5b032c5fc2edf1ddf72e5a414485fda512e21 quitOnLastWindowClosed
was changed to be implemented in terms of quitLockEnabled, but without
any documentation to that end.

Although the two features are similar (automatic quit under certain
conditions), and interact, it doesn't make sense to overlap them until
we actually expose them as a single property (automaticQuit e.g.)

The logic for determining whether we can can quit automatically has
been refactored to take both properties into account, on both a Core
and Gui level. The call sites still need to check the individual
properties to determine whether to activate automatic quit for
that particular code path.

Change-Id: I38c3e8cb30db373ea73dd45f150e5048c0db2f4d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

4 files changed, 43 insertions, 20 deletions

diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index 727fc825e0..c980e70dbf 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -400,7 +400,7 @@ struct QCoreApplicationData {
 Q_GLOBAL_STATIC(QCoreApplicationData, coreappdata)
 
 #ifndef QT_NO_QOBJECT
-static bool quitLockRefEnabled = true;
+static bool quitLockEnabled = true;
 #endif
 
 #if defined(Q_OS_WIN)
@@ -1020,14 +1020,14 @@ bool QCoreApplication::testAttribute(Qt::ApplicationAttribute attribute)
 
 bool QCoreApplication::isQuitLockEnabled()
 {
-    return quitLockRefEnabled;
+    return quitLockEnabled;
 }
 
 static bool doNotify(QObject *, QEvent *);
 
 void QCoreApplication::setQuitLockEnabled(bool enabled)
 {
-    quitLockRefEnabled = enabled;
+    quitLockEnabled = enabled;
 }
 
 /*!
@@ -1982,14 +1982,34 @@ void QCoreApplicationPrivate::ref()
 
 void QCoreApplicationPrivate::deref()
 {
-    if (!quitLockRef.deref())
-        maybeQuit();
+    quitLockRef.deref();
+
+    if (quitLockEnabled && canQuitAutomatically())
+        quitAutomatically();
 }
 
-void QCoreApplicationPrivate::maybeQuit()
+bool QCoreApplicationPrivate::canQuitAutomatically()
 {
-    if (quitLockRef.loadRelaxed() == 0 && in_exec && quitLockRefEnabled && shouldQuit())
-        QCoreApplication::postEvent(QCoreApplication::instance(), new QEvent(QEvent::Quit));
+    if (!in_exec)
+        return false;
+
+    if (quitLockEnabled && quitLockRef.loadRelaxed())
+        return false;
+
+    return true;
+}
+
+void QCoreApplicationPrivate::quitAutomatically()
+{
+    Q_Q(QCoreApplication);
+
+    // Explicit requests by the user to quit() is plumbed via the platform
+    // if possible, and delivers the quit event synchronously. For automatic
+    // quits we implicitly support cancelling the quit by showing another
+    // window, which currently relies on removing any posted quit events
+    // from the event queue. As a result, we can't use the normal quit()
+    // code path, and need to post manually.
+    QCoreApplication::postEvent(q, new QEvent(QEvent::Quit));
 }
 
 /*!
diff --git a/src/corelib/kernel/qcoreapplication_p.h b/src/corelib/kernel/qcoreapplication_p.h
index ae1e1cd4e9..132be9effc 100644
--- a/src/corelib/kernel/qcoreapplication_p.h
+++ b/src/corelib/kernel/qcoreapplication_p.h
@@ -136,12 +136,9 @@ public:
     QAtomicInt quitLockRef;
     void ref();
     void deref();
-    virtual bool shouldQuit() {
-      return true;
-    }
-
+    virtual bool canQuitAutomatically();
+    void quitAutomatically();
     virtual void quit();
-    void maybeQuit();
 
     static QBasicAtomicPointer<QThread> theMainThread;
     static QThread *mainThread();
diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 2ca1ff0a44..8f9c2bd996 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -210,6 +210,8 @@ qreal QGuiApplicationPrivate::m_maxDevicePixelRatio = 0.0;
 
 static qreal fontSmoothingGamma = 1.7;
 
+bool QGuiApplicationPrivate::quitOnLastWindowClosed = true;
+
 extern void qRegisterGuiVariant();
 #if QT_CONFIG(animation)
 extern void qRegisterGuiGetInterpolator();
@@ -3538,12 +3540,12 @@ void QGuiApplicationPrivate::notifyWindowIconChanged()
 
 void QGuiApplication::setQuitOnLastWindowClosed(bool quit)
 {
-    QCoreApplication::setQuitLockEnabled(quit);
+    QGuiApplicationPrivate::quitOnLastWindowClosed = quit;
 }
 
 bool QGuiApplication::quitOnLastWindowClosed()
 {
-    return QCoreApplication::isQuitLockEnabled();
+    return QGuiApplicationPrivate::quitOnLastWindowClosed;
 }
 
 void QGuiApplicationPrivate::maybeLastWindowClosed(QWindow *closedWindow)
@@ -3561,8 +3563,8 @@ void QGuiApplicationPrivate::maybeLastWindowClosed(QWindow *closedWindow)
     if (in_exec)
         emit q_func()->lastWindowClosed();
 
-    if (QGuiApplication::quitOnLastWindowClosed())
-        maybeQuit();
+    if (quitOnLastWindowClosed && canQuitAutomatically())
+        quitAutomatically();
 }
 
 /*!
@@ -3591,9 +3593,12 @@ bool QGuiApplicationPrivate::lastWindowClosed() const
      return true;
 }
 
-bool QGuiApplicationPrivate::shouldQuit()
+bool QGuiApplicationPrivate::canQuitAutomatically()
 {
-    return lastWindowClosed();
+    if (quitOnLastWindowClosed && !lastWindowClosed())
+        return false;
+
+    return QCoreApplicationPrivate::canQuitAutomatically();
 }
 
 void QGuiApplicationPrivate::quit()
diff --git a/src/gui/kernel/qguiapplication_p.h b/src/gui/kernel/qguiapplication_p.h
index d43bfd755e..92d69f4a76 100644
--- a/src/gui/kernel/qguiapplication_p.h
+++ b/src/gui/kernel/qguiapplication_p.h
@@ -105,11 +105,12 @@ public:
 #if QT_CONFIG(commandlineparser)
     void addQtOptions(QList<QCommandLineOption> *options) override;
 #endif
-    virtual bool shouldQuit() override;
+    bool canQuitAutomatically() override;
     void quit() override;
 
     void maybeLastWindowClosed(QWindow *closedWindow);
     bool lastWindowClosed() const;
+    static bool quitOnLastWindowClosed;
 
     static void captureGlobalModifierState(QEvent *e);
     static Qt::KeyboardModifiers modifier_buttons;