[game_list] fix crash and flashing from the directory watcher (#4099)

So the game list watcher could rebuild the content providers
(CreateFactories) while the populate worker was still scanning them, and
the worker would walk a torn-down RegisteredCache and segfault in
OpenFileOrDirectoryConcat. Fixed by stopping and joining the worker
before rebuilding.

On macOS the watcher also re-armed itself every populate. Re-adding the
same paths makes QFileSystemWatcher re-emit directoryChanged (the
FSEvent comes in async, so the blockSignals guard misses it), so it just
kept refreshing and the list flashed forever. Now it only re-arms when
the watched dirs actually changed.

Also null-guarded OpenFileOrDirectoryConcat so a torn-down cache cant
null-deref there.

Related: https://github.com/eden-emulator/Issue-Reports/issues/336
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4099
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

2 files changed, 12 insertions, 0 deletions

diff --git a/src/qt_common/game_list/model.cpp b/src/qt_common/game_list/model.cpp
index 2f8deaa0c5..91ec80c525 100644
--- a/src/qt_common/game_list/model.cpp
+++ b/src/qt_common/game_list/model.cpp
@@ -57,6 +57,12 @@ void GameListModel::PopulateAsync(QVector<UISettings::GameDir>& game_dirs) {
     QThreadPool::globalInstance()->start(current_worker.get());
 }
 
+void GameListModel::StopWorker() {
+    // ~GameListWorker sets stop_requested and blocks until run() finishes, so this returns only
+    // once the worker is no longer touching the content providers.
+    current_worker.reset();
+}
+
 void GameListModel::WorkerEvent() {
     current_worker->ProcessEvents(this);
 }
@@ -202,6 +208,7 @@ void GameListModel::RefreshGameDirectory() {
 
     if (!UISettings::values.game_dirs.empty() && current_worker != nullptr) {
         LOG_INFO(Frontend, "Change detected in the games directory. Reloading game list.");
+        StopWorker();
         QtCommon::system->GetFileSystemController().CreateFactories(*QtCommon::vfs);
         PopulateAsync(UISettings::values.game_dirs);
     }
@@ -210,6 +217,7 @@ void GameListModel::RefreshGameDirectory() {
 void GameListModel::RefreshExternalContent() {
     if (!UISettings::values.game_dirs.empty() && current_worker != nullptr) {
         LOG_INFO(Frontend, "External content directory changed. Clearing metadata cache.");
+        StopWorker();
         QtCommon::Game::ResetMetadata(false);
         QtCommon::system->GetFileSystemController().CreateFactories(*QtCommon::vfs);
         PopulateAsync(UISettings::values.game_dirs);
diff --git a/src/qt_common/game_list/model.h b/src/qt_common/game_list/model.h
index d0a116beb6..ce1fcc87b7 100644
--- a/src/qt_common/game_list/model.h
+++ b/src/qt_common/game_list/model.h
@@ -52,6 +52,10 @@ public:
     void DonePopulating(const QStringList& watch_list);
 
     void PopulateAsync(QVector<UISettings::GameDir>& game_dirs);
+    // Stops and joins the running populate worker, if any. Must be called before rebuilding the
+    // content providers (CreateFactories), otherwise the worker keeps scanning a cache that is
+    // being torn down underneath it.
+    void StopWorker();
     void WorkerEvent();
 
     bool IsEmpty() const;