GUI: only clean the cache once per version

The process can take a lot of time, therefore only do it if there's a
reasonable chance that files will have to be cleaned up — which is after
a version change.

Another piece of the fix for #1860.

NEWS.md

@@ -28,7 +28,8 @@
 ## Bug fixes
 
 * GUI: the cache cleanup process that's run automatically when the GUI starts
-  no longer blocks file identification until it is finished. Fixes #1860.
+  no longer blocks file identification until it is finished. Additionally the
+  process will only be run once per release of MKVToolNix. Fixes #1860.
 * GUI: certain failures during file identification that can be traced to
   broken installations (e.g. mkvmerge being too old) won't be stored in the
   cache anymore. Without this fix the GUI would still use the cached failed

src/mkvtoolnix-gui/main_window/main_window.cpp

@@ -74,7 +74,7 @@ MainWindow::MainWindow(QWidget *parent)
   new TaskbarProgress{this};
 #endif
 
-  QtConcurrent::run(Util::Cache::cleanOldCacheFiles);
+  runCacheCleanupOncePerVersion();
 
   Util::InstallationChecker::checkInstallation();
 }
@@ -608,4 +608,12 @@ MainWindow::displayInstallationProblems(Util::InstallationChecker::Problems cons
     .exec();
 }
 
+void
+MainWindow::runCacheCleanupOncePerVersion()
+  const {
+  Util::Settings::runOncePerVersion(Q("cacheCleanup"), []() {
+    QtConcurrent::run(Util::Cache::cleanOldCacheFiles);
+  });
+}
+
 }}

src/mkvtoolnix-gui/main_window/main_window.h

@@ -126,6 +126,7 @@ protected:
   virtual boost::optional<bool> filterWheelEventForStrongFocus(QObject *watched, QEvent *event);
 
   virtual void silentlyCheckForUpdates();
+  virtual void runCacheCleanupOncePerVersion() const;
 };
 
 }}

src/mkvtoolnix-gui/util/settings.cpp

@@ -619,4 +619,23 @@ Settings::lastOpenDirPath()
   return Util::dirPath(m_lastOpenDir);
 }
 
+void
+Settings::runOncePerVersion(QString const &topic,
+                            std::function<void()> worker) {
+  auto reg = registry();
+  auto key = Q("runOncePerVersion/%1").arg(topic);
+
+  auto lastRunInVersion       = reg->value(key).toString();
+  auto lastRunInVersionNumber = version_number_t{to_utf8(lastRunInVersion)};
+  auto currentVersionNumber   = get_current_version();
+
+  if (   lastRunInVersionNumber.valid
+      && !(lastRunInVersionNumber < currentVersionNumber))
+    return;
+
+  reg->setValue(key, Q(currentVersionNumber.to_string()));
+
+  worker();
+}
+
 }}}

src/mkvtoolnix-gui/util/settings.h

@@ -188,6 +188,8 @@ public:
   static void change(std::function<void(Settings &)> worker);
   static std::unique_ptr<QSettings> registry();
 
+  static void runOncePerVersion(QString const &topic, std::function<void()> worker);
+
   static QString exeWithPath(QString const &exe);
 
   static void migrateFromRegistry();