Fix potential thread-safety on lazy media format initialization

Let's have a common approach of lazy media format initialization
for all platforms.

The approach was introduced in some recent CR, but it hasn't been
integrated due to other reasons.

Pick-to: 6.5 6.6
Change-Id: I0fff558463753149d2381a2435f8ba300243f0a8
Reviewed-by: Pavel Dubsky <pavel.dubsky@qt.io>
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>

2 files changed, 23 insertions, 2 deletions

diff --git a/src/multimedia/platform/qplatformmediaintegration.cpp b/src/multimedia/platform/qplatformmediaintegration.cpp
index b094d549c..1fe5e1cd1 100644
--- a/src/multimedia/platform/qplatformmediaintegration.cpp
+++ b/src/multimedia/platform/qplatformmediaintegration.cpp
@@ -14,6 +14,7 @@
 
 #include "qplatformcapturablewindows_p.h"
 #include "QtCore/private/qfactoryloader_p.h"
+#include "private/qplatformmediaformatinfo_p.h"
 #include "qplatformmediaplugin_p.h"
 
 class QDummyIntegration : public QPlatformMediaIntegration
@@ -23,7 +24,6 @@ public:
     {
         qCritical("QtMultimedia is not currently supported on this platform or compiler.");
     }
-    QPlatformMediaFormatInfo *formatInfo() override { return nullptr; }
 };
 
 static Q_LOGGING_CATEGORY(qLcMediaPlugin, "qt.multimedia.plugin")
@@ -144,6 +144,20 @@ bool QPlatformMediaIntegration::isCapturableWindowValid(const QCapturableWindowP
     return m_capturableWindows && m_capturableWindows->isWindowValid(window);
 }
 
+const QPlatformMediaFormatInfo *QPlatformMediaIntegration::formatInfo()
+{
+    std::call_once(m_formatInfoOnceFlg, [this]() {
+        m_formatInfo.reset(createFormatInfo());
+        Q_ASSERT(m_formatInfo);
+    });
+    return m_formatInfo.get();
+}
+
+QPlatformMediaFormatInfo *QPlatformMediaIntegration::createFormatInfo()
+{
+    return new QPlatformMediaFormatInfo;
+}
+
 QPlatformMediaIntegration::QPlatformMediaIntegration() = default;
 
 QPlatformMediaIntegration::~QPlatformMediaIntegration() = default;
diff --git a/src/multimedia/platform/qplatformmediaintegration_p.h b/src/multimedia/platform/qplatformmediaintegration_p.h
index 728425355..3fc97a1ce 100644
--- a/src/multimedia/platform/qplatformmediaintegration_p.h
+++ b/src/multimedia/platform/qplatformmediaintegration_p.h
@@ -21,6 +21,7 @@
 #include <qstring.h>
 
 #include <memory>
+#include <mutex>
 
 QT_BEGIN_NAMESPACE
 
@@ -60,7 +61,7 @@ public:
 
     QPlatformMediaIntegration();
     virtual ~QPlatformMediaIntegration();
-    virtual QPlatformMediaFormatInfo *formatInfo() = 0;
+    const QPlatformMediaFormatInfo *formatInfo();
 
     virtual QList<QCameraDevice> videoInputs();
     virtual QMaybe<QPlatformCamera *> createCamera(QCamera *) { return notAvailable; }
@@ -83,6 +84,9 @@ public:
 
     QPlatformVideoDevices *videoDevices() { return m_videoDevices.get(); }
 
+protected:
+    virtual QPlatformMediaFormatInfo *createFormatInfo();
+
 private:
     friend class QMockIntegrationFactory;
     // API to be able to test with a mock backend
@@ -93,6 +97,9 @@ private:
 protected:
     std::unique_ptr<QPlatformVideoDevices> m_videoDevices;
     std::unique_ptr<QPlatformCapturableWindows> m_capturableWindows;
+
+    mutable std::unique_ptr<QPlatformMediaFormatInfo> m_formatInfo;
+    mutable std::once_flag m_formatInfoOnceFlg;
 };
 
 QT_END_NAMESPACE