Make singletons easier to spot using Q_GLOBAL_STATIC

In QtMultimedia we have some singletons that are a bit hard to see in
the code. It would be good if we can easily search for singleton
objects.

This patch makes these singletons easier to identify by using the
Q_GLOBAL_STATIC macro.

Pick-to: 6.7 6.6 6.5
Change-Id: I921230fdcc6e34c4a311dd2f1a22e7741ccf31b6
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>

4 files changed, 54 insertions, 47 deletions

diff --git a/src/multimedia/platform/qplatformmediadevices.cpp b/src/multimedia/platform/qplatformmediadevices.cpp
index a9d591ee8..61b6515e6 100644
--- a/src/multimedia/platform/qplatformmediadevices.cpp
+++ b/src/multimedia/platform/qplatformmediadevices.cpp
@@ -53,32 +53,32 @@ struct DevicesHolder
     QPlatformMediaDevices *nativeInstance = nullptr;
 };
 
-DevicesHolder devicesHolder;
+Q_GLOBAL_STATIC(DevicesHolder, devicesHolder);
 
 }
 
 QPlatformMediaDevices *QPlatformMediaDevices::instance()
 {
-    QMutexLocker locker(&devicesHolder.mutex);
-    if (devicesHolder.instance)
-        return devicesHolder.instance;
+    QMutexLocker locker(&devicesHolder->mutex);
+    if (devicesHolder->instance)
+        return devicesHolder->instance;
 
 #ifdef Q_OS_DARWIN
-    devicesHolder.nativeInstance = new QDarwinMediaDevices;
+    devicesHolder->nativeInstance = new QDarwinMediaDevices;
 #elif defined(Q_OS_WINDOWS)
-    devicesHolder.nativeInstance = new QWindowsMediaDevices;
+    devicesHolder->nativeInstance = new QWindowsMediaDevices;
 #elif defined(Q_OS_ANDROID)
-    devicesHolder.nativeInstance = new QAndroidMediaDevices;
+    devicesHolder->nativeInstance = new QAndroidMediaDevices;
 #elif QT_CONFIG(alsa)
-    devicesHolder.nativeInstance = new QAlsaMediaDevices;
+    devicesHolder->nativeInstance = new QAlsaMediaDevices;
 #elif QT_CONFIG(pulseaudio)
-    devicesHolder.nativeInstance = new QPulseAudioMediaDevices;
+    devicesHolder->nativeInstance = new QPulseAudioMediaDevices;
 #elif defined(Q_OS_QNX)
-    devicesHolder.nativeInstance = new QQnxMediaDevices;
+    devicesHolder->nativeInstance = new QQnxMediaDevices;
 #elif defined(Q_OS_WASM)
-    devicesHolder.nativeInstance = new QWasmMediaDevices;
+    devicesHolder->nativeInstance = new QWasmMediaDevices;
 #else
-    devicesHolder.nativeInstance = new QPlatformMediaDevices;
+    devicesHolder->nativeInstance = new QPlatformMediaDevices;
 #endif
 
     if (!QCoreApplication::instance()) {
@@ -86,13 +86,13 @@ QPlatformMediaDevices *QPlatformMediaDevices::instance()
         // application with Windows backend.
         qWarning("Accessing QMediaDevices without a QCoreApplication");
     } else {
-        connect(qApp, &QObject::destroyed, devicesHolder.nativeInstance, []() {
-            devicesHolder.reset();
+        connect(qApp, &QObject::destroyed, devicesHolder->nativeInstance, []() {
+            devicesHolder->reset();
         });
     }
 
-    devicesHolder.instance = devicesHolder.nativeInstance;
-    return devicesHolder.instance;
+    devicesHolder->instance = devicesHolder->nativeInstance;
+    return devicesHolder->instance;
 }
 
 
@@ -111,7 +111,7 @@ void QPlatformMediaDevices::initVideoDevicesConnection() {
 
 void QPlatformMediaDevices::setDevices(QPlatformMediaDevices *devices)
 {
-    devicesHolder.instance = devices;
+    devicesHolder->instance = devices;
 }
 
 QPlatformMediaDevices::~QPlatformMediaDevices() = default;
diff --git a/src/multimedia/platform/qplatformmediaintegration.cpp b/src/multimedia/platform/qplatformmediaintegration.cpp
index eee36beff..e4258a179 100644
--- a/src/multimedia/platform/qplatformmediaintegration.cpp
+++ b/src/multimedia/platform/qplatformmediaintegration.cpp
@@ -71,25 +71,31 @@ static QString defaultBackend(const QStringList &backends)
     return backends[0];
 }
 
-QT_BEGIN_NAMESPACE
+namespace {
 
-struct QPlatformMediaIntegration::InstanceHolder
+struct InstanceHolder
 {
     // TODO: replace the mutex with std::once
     QBasicMutex mutex;
     std::unique_ptr<QPlatformMediaIntegration> instance;
-    Factory factory;
-} instanceHolder;
+    std::function<std::unique_ptr<QPlatformMediaIntegration>()> factory;
+};
+
+Q_GLOBAL_STATIC(InstanceHolder, instanceHolder);
+
+} // namespace
+
+QT_BEGIN_NAMESPACE
 
 QPlatformMediaIntegration *QPlatformMediaIntegration::instance()
 {
-    QMutexLocker locker(&instanceHolder.mutex);
-    if (instanceHolder.instance)
-        return instanceHolder.instance.get();
+    QMutexLocker locker(&instanceHolder->mutex);
+    if (instanceHolder->instance)
+        return instanceHolder->instance.get();
 
-    if (instanceHolder.factory) {
-        instanceHolder.instance = instanceHolder.factory();
-        return instanceHolder.instance.get();
+    if (instanceHolder->factory) {
+        instanceHolder->instance = instanceHolder->factory();
+        return instanceHolder->instance.get();
     }
 
     const auto backends = availableBackends();
@@ -98,25 +104,25 @@ QPlatformMediaIntegration *QPlatformMediaIntegration::instance()
         backend = defaultBackend(backends);
 
     qCDebug(qLcMediaPlugin) << "loading backend" << backend;
-    instanceHolder.instance.reset(
+    instanceHolder->instance.reset(
             qLoadPlugin<QPlatformMediaIntegration, QPlatformMediaPlugin>(loader(), backend));
 
-    if (!instanceHolder.instance) {
+    if (!instanceHolder->instance) {
         qWarning() << "could not load multimedia backend" << backend;
-        instanceHolder.instance = std::make_unique<QDummyIntegration>();
+        instanceHolder->instance = std::make_unique<QDummyIntegration>();
     }
 
-    return instanceHolder.instance.get();
+    return instanceHolder->instance.get();
 }
 
 /*
     This API is there to be able to test with a mock backend.
 */
-void QPlatformMediaIntegration::setPlatformFactory(Factory factory)
+void QPlatformMediaIntegration::setPlatformFactory(std::function<std::unique_ptr<QPlatformMediaIntegration>()> factory)
 {
-    Q_ASSERT((factory == nullptr) ^ (instanceHolder.factory == nullptr));
-    instanceHolder.instance.reset();
-    instanceHolder.factory = std::move(factory);
+    Q_ASSERT((factory == nullptr) ^ (instanceHolder->factory == nullptr));
+    instanceHolder->instance.reset();
+    instanceHolder->factory = std::move(factory);
 }
 
 QList<QCameraDevice> QPlatformMediaIntegration::videoInputs()
diff --git a/src/multimedia/platform/qplatformmediaintegration_p.h b/src/multimedia/platform/qplatformmediaintegration_p.h
index 21891b866..10845326c 100644
--- a/src/multimedia/platform/qplatformmediaintegration_p.h
+++ b/src/multimedia/platform/qplatformmediaintegration_p.h
@@ -103,9 +103,7 @@ protected:
 private:
     friend class QMockIntegrationFactory;
     // API to be able to test with a mock backend
-    using Factory = std::function<std::unique_ptr<QPlatformMediaIntegration>()>;
-    struct InstanceHolder;
-    static void setPlatformFactory(Factory factory);
+    static void setPlatformFactory(std::function<std::unique_ptr<QPlatformMediaIntegration>()> factory);
 
 private:
     std::unique_ptr<QPlatformVideoDevices> m_videoDevices;
diff --git a/src/multimedia/windows/qwindowsmediafoundation.cpp b/src/multimedia/windows/qwindowsmediafoundation.cpp
index 55b2f5459..9b67e9e63 100644
--- a/src/multimedia/windows/qwindowsmediafoundation.cpp
+++ b/src/multimedia/windows/qwindowsmediafoundation.cpp
@@ -9,6 +9,7 @@
 QT_BEGIN_NAMESPACE
 
 namespace {
+
 struct Holder {
     ~Holder()
     {
@@ -18,9 +19,11 @@ struct Holder {
     bool loadFailed = false;
     QBasicMutex mutex;
     std::unique_ptr<QWindowsMediaFoundation> instance;
-} holder;
+};
 
-}
+Q_GLOBAL_STATIC(Holder, holder)
+
+} // namespace
 
 QWindowsMediaFoundation::~QWindowsMediaFoundation() = default;
 
@@ -32,11 +35,11 @@ template<typename T> bool setProcAddress(QSystemLibrary &lib, T &f, std::string_
 
 QWindowsMediaFoundation *QWindowsMediaFoundation::instance()
 {
-    QMutexLocker locker(&holder.mutex);
-    if (holder.instance)
-        return holder.instance.get();
+    QMutexLocker locker(&holder->mutex);
+    if (holder->instance)
+        return holder->instance.get();
 
-    if (holder.loadFailed)
+    if (holder->loadFailed)
         return nullptr;
 
     std::unique_ptr<QWindowsMediaFoundation> wmf(new QWindowsMediaFoundation);
@@ -45,12 +48,12 @@ QWindowsMediaFoundation *QWindowsMediaFoundation::instance()
             && setProcAddress(wmf->m_mfplat, wmf->mfCreateMemoryBuffer, "MFCreateMemoryBuffer")
             && setProcAddress(wmf->m_mfplat, wmf->mfCreateSample, "MFCreateSample"))
         {
-            holder.instance = std::move(wmf);
-            return holder.instance.get();
+            holder->instance = std::move(wmf);
+            return holder->instance.get();
         }
     }
 
-    holder.loadFailed = true;
+    holder->loadFailed = true;
     return nullptr;
 }