Add Q_COREAPP_STARTUP_FUNCTION macro.

This is necessary for initializing things in a library, which require
a QCoreApplication instance (unlike Q_CONSTRUCTOR_FUNCTION, which runs
before that). Example use cases: KCrash (segv handler), and KCheckAccelerators
(debugging tool triggered by magic key combination).

Change-Id: I5f4c4699dd4d21aea72b007989ba57467e86ed10
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/doc/snippets/code/src_corelib_kernel_qcoreapplication.cpp

@@ -57,7 +57,14 @@ foreach (const QString &path, app.libraryPaths())
 
 
 //! [3]
+// Called once QCoreApplication exists
+static void preRoutineMyDebugTool()
+{
+    MyDebugTool* tool = new MyDebugTool(QCoreApplication::instance());
+    QCoreApplication::instance()->installEventFilter(tool);
+}
 
+Q_COREAPP_STARTUP_FUNCTION(preRoutineMyDebugTool)
 //! [3]
 
 

src/corelib/kernel/qcoreapplication.cpp

@@ -194,8 +194,32 @@ extern "C" void Q_CORE_EXPORT qt_startup_hook()
 {
 }
 
+typedef QList<QtStartUpFunction> QStartUpFuncList;
+Q_GLOBAL_STATIC(QStartUpFuncList, preRList)
 typedef QList<QtCleanUpFunction> QVFuncList;
 Q_GLOBAL_STATIC(QVFuncList, postRList)
+static QBasicMutex globalPreRoutinesMutex;
+
+/*!
+    \internal
+
+    Adds a global routine that will be called from the QCoreApplication
+    constructor. The public API is Q_COREAPP_STARTUP_FUNCTION.
+*/
+void qAddPreRoutine(QtStartUpFunction p)
+{
+    QStartUpFuncList *list = preRList();
+    if (!list)
+        return;
+    // Due to C++11 parallel dynamic initialization, this can be called
+    // from multiple threads.
+#ifndef QT_NO_THREAD
+    QMutexLocker locker(&globalPreRoutinesMutex);
+#endif
+    if (QCoreApplication::instance())
+        p();
+    list->prepend(p); // in case QCoreApplication is re-created, see qt_call_pre_routines
+}
 
 void qAddPostRoutine(QtCleanUpFunction p)
 {
@@ -213,6 +237,21 @@ void qRemovePostRoutine(QtCleanUpFunction p)
     list->removeAll(p);
 }
 
+static void qt_call_pre_routines()
+{
+    QStartUpFuncList *list = preRList();
+    if (!list)
+        return;
+#ifndef QT_NO_THREAD
+    QMutexLocker locker(&globalPreRoutinesMutex);
+#endif
+    // Unlike qt_call_post_routines, we don't empty the list, because
+    // Q_COREAPP_STARTUP_FUNCTION is a macro, so the user expects
+    // the function to be executed every time QCoreApplication is created.
+    for (int i = 0; i < list->count(); ++i)
+        list->at(i)();
+}
+
 void Q_CORE_EXPORT qt_call_post_routines()
 {
     QVFuncList *list = 0;
@@ -637,6 +676,7 @@ void QCoreApplication::init()
 
     d->processCommandLineArguments();
 
+    qt_call_pre_routines();
     qt_startup_hook();
 }
 
@@ -2324,6 +2364,31 @@ void QCoreApplication::setEventDispatcher(QAbstractEventDispatcher *eventDispatc
     mainThread->setEventDispatcher(eventDispatcher);
 }
 
+/*!
+    \macro Q_COREAPP_STARTUP_FUNCTION(QtStartUpFunction ptr)
+    \since 5.1
+    \relates QCoreApplication
+    \reentrant
+
+    Adds a global function that will be called from the QCoreApplication
+    constructor. This macro is normally used to initialize libraries
+    for program-wide functionality, without requiring the application to
+    call into the library for initialization.
+
+    The function specified by \a ptr should take no arguments and should
+    return nothing. For example:
+
+    \snippet code/src_corelib_kernel_qcoreapplication.cpp 3
+
+    Note that the startup function will run at the end of the QCoreApplication constructor,
+    before any GUI initialization. If GUI code is required in the function,
+    use a timer (or a queued invocation) to perform the initialization later on,
+    from the event loop.
+
+    If QCoreApplication is deleted and another QCoreApplication is created,
+    the startup function will be invoked again.
+*/
+
 /*!
     \fn void qAddPostRoutine(QtCleanUpFunction ptr)
     \relates QCoreApplication

src/corelib/kernel/qcoreapplication.h

@@ -220,12 +220,20 @@ public: \
         { return QCoreApplication::translate(#context, sourceText, disambiguation, n); } \
 private:
 
+typedef void (*QtStartUpFunction)();
 typedef void (*QtCleanUpFunction)();
 
+Q_CORE_EXPORT void qAddPreRoutine(QtStartUpFunction);
 Q_CORE_EXPORT void qAddPostRoutine(QtCleanUpFunction);
 Q_CORE_EXPORT void qRemovePostRoutine(QtCleanUpFunction);
 Q_CORE_EXPORT QString qAppName();                // get application name
 
+#define Q_COREAPP_STARTUP_FUNCTION(AFUNC) \
+    static void AFUNC ## _ctor_function() {  \
+        qAddPreRoutine(AFUNC);        \
+    }                                 \
+    Q_CONSTRUCTOR_FUNCTION(AFUNC ## _ctor_function)
+
 #if defined(Q_OS_WIN) && !defined(QT_NO_DEBUG_STREAM)
 Q_CORE_EXPORT QString decodeMSG(const MSG &);
 Q_CORE_EXPORT QDebug operator<<(QDebug, const MSG &);

tests/auto/corelib/global/qglobal/tst_qglobal.cpp

@@ -55,6 +55,8 @@ private slots:
     void checkptr();
     void qstaticassert();
     void qConstructorFunction();
+    void qCoreAppStartupFunction();
+    void qCoreAppStartupFunctionRestart();
     void isEnum();
     void qAlignOf();
 };
@@ -303,6 +305,33 @@ void tst_QGlobal::qConstructorFunction()
     QCOMPARE(qConstructorFunctionValue, 123);
 }
 
+static int qStartupFunctionValue;
+static void myStartupFunc()
+{
+   Q_ASSERT(QCoreApplication::instance());
+   if (QCoreApplication::instance())
+       qStartupFunctionValue += 124;
+}
+
+Q_COREAPP_STARTUP_FUNCTION(myStartupFunc)
+
+void tst_QGlobal::qCoreAppStartupFunction()
+{
+    QCOMPARE(qStartupFunctionValue, 0);
+    int argc = 1;
+    char *argv[] = { const_cast<char*>("tst_qglobal") };
+    QCoreApplication app(argc, argv);
+    QCOMPARE(qStartupFunctionValue, 124);
+}
+
+void tst_QGlobal::qCoreAppStartupFunctionRestart()
+{
+    qStartupFunctionValue = 0;
+    qCoreAppStartupFunction();
+    qStartupFunctionValue = 0;
+    qCoreAppStartupFunction();
+}
+
 struct isEnum_A {
     int n_;
 };
@@ -532,5 +561,5 @@ void tst_QGlobal::qAlignOf()
 #undef TEST_AlignOf_RValueRef
 #undef TEST_AlignOf_impl
 
-QTEST_MAIN(tst_QGlobal)
+QTEST_APPLESS_MAIN(tst_QGlobal)
 #include "tst_qglobal.moc"