Implement lazy initialization of CapturableWindows

The patch initializes CapturableWindows lazily as its instance is
needed only in specific cases.

Pick-to: 6.7 6.6
Change-Id: Ib80dc92b44127a908f47ec893235bece6ec2ef40
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
Reviewed-by: Jøger Hansegård <joger.hansegard@qt.io>

3 files changed, 21 insertions, 9 deletions

diff --git a/src/multimedia/platform/qplatformmediaintegration.cpp b/src/multimedia/platform/qplatformmediaintegration.cpp
index 5abed10f4..eee36beff 100644
--- a/src/multimedia/platform/qplatformmediaintegration.cpp
+++ b/src/multimedia/platform/qplatformmediaintegration.cpp
@@ -135,14 +135,16 @@ QMaybe<QPlatformAudioOutput *> QPlatformMediaIntegration::createAudioOutput(QAud
     return new QPlatformAudioOutput(q);
 }
 
-QList<QCapturableWindow> QPlatformMediaIntegration::capturableWindows()
+QList<QCapturableWindow> QPlatformMediaIntegration::capturableWindowsList()
 {
-    return m_capturableWindows ? m_capturableWindows->windows() : QList<QCapturableWindow>{};
+    const auto capturableWindows = this->capturableWindows();
+    return capturableWindows ? capturableWindows->windows() : QList<QCapturableWindow>{};
 }
 
 bool QPlatformMediaIntegration::isCapturableWindowValid(const QCapturableWindowPrivate &window)
 {
-    return m_capturableWindows && m_capturableWindows->isWindowValid(window);
+    const auto capturableWindows = this->capturableWindows();
+    return capturableWindows && capturableWindows->isWindowValid(window);
 }
 
 const QPlatformMediaFormatInfo *QPlatformMediaIntegration::formatInfo()
@@ -166,6 +168,13 @@ QPlatformVideoDevices *QPlatformMediaIntegration::videoDevices()
     return m_videoDevices.get();
 }
 
+QPlatformCapturableWindows *QPlatformMediaIntegration::capturableWindows()
+{
+    std::call_once(m_capturableWindowsOnceFlag,
+                   [this]() { m_capturableWindows.reset(createCapturableWindows()); });
+    return m_capturableWindows.get();
+}
+
 QPlatformMediaIntegration::QPlatformMediaIntegration() = default;
 
 QPlatformMediaIntegration::~QPlatformMediaIntegration() = default;
diff --git a/src/multimedia/platform/qplatformmediaintegration_p.h b/src/multimedia/platform/qplatformmediaintegration_p.h
index 6755797d9..cc40627d0 100644
--- a/src/multimedia/platform/qplatformmediaintegration_p.h
+++ b/src/multimedia/platform/qplatformmediaintegration_p.h
@@ -79,16 +79,20 @@ public:
 
     virtual QMaybe<QPlatformVideoSink *> createVideoSink(QVideoSink *) { return notAvailable; }
 
-    QList<QCapturableWindow> capturableWindows();
+    QList<QCapturableWindow> capturableWindowsList();
     bool isCapturableWindowValid(const QCapturableWindowPrivate &);
 
     QPlatformVideoDevices *videoDevices();
 
+    QPlatformCapturableWindows *capturableWindows();
+
 protected:
     virtual QPlatformMediaFormatInfo *createFormatInfo();
 
     virtual QPlatformVideoDevices *createVideoDevices() { return nullptr; }
 
+    virtual QPlatformCapturableWindows *createCapturableWindows() { return nullptr; }
+
 private:
     friend class QMockIntegrationFactory;
     // API to be able to test with a mock backend
@@ -96,14 +100,13 @@ private:
     struct InstanceHolder;
     static void setPlatformFactory(Factory factory);
 
-protected:
-    // TODO: initialize via once_flag and move to private
-    std::unique_ptr<QPlatformCapturableWindows> m_capturableWindows;
-
 private:
     std::unique_ptr<QPlatformVideoDevices> m_videoDevices;
     std::once_flag m_videoDevicesOnceFlag;
 
+    std::unique_ptr<QPlatformCapturableWindows> m_capturableWindows;
+    std::once_flag m_capturableWindowsOnceFlag;
+
     mutable std::unique_ptr<QPlatformMediaFormatInfo> m_formatInfo;
     mutable std::once_flag m_formatInfoOnceFlg;
 };
diff --git a/src/multimedia/recording/qwindowcapture.cpp b/src/multimedia/recording/qwindowcapture.cpp
index ef4417235..69ad60100 100644
--- a/src/multimedia/recording/qwindowcapture.cpp
+++ b/src/multimedia/recording/qwindowcapture.cpp
@@ -119,7 +119,7 @@ QWindowCapture::~QWindowCapture()
  */
 QList<QCapturableWindow> QWindowCapture::capturableWindows()
 {
-    return QPlatformMediaIntegration::instance()->capturableWindows();
+    return QPlatformMediaIntegration::instance()->capturableWindowsList();
 }
 
 QMediaCaptureSession *QWindowCapture::captureSession() const