db/update: cancel the update on shutdown

NEWS

@@ -9,6 +9,7 @@ ver 0.19 (not yet released)
   - proxy: forward "idle" events
   - proxy: copy "Last-Modified" from remote directories
   - upnp: new plugin
+  - cancel the update on shutdown
 * storage
   - music_directory can point to a remote file server
   - nfs: new plugin

src/Main.cxx

@@ -596,6 +596,9 @@ int mpd_main(int argc, char *argv[])
 
 #if defined(ENABLE_DATABASE) && defined(ENABLE_INOTIFY)
 	mpd_inotify_finish();
+
+	if (instance->update != nullptr)
+		instance->update->CancelAllAsync();
 #endif
 
 	if (state_file != nullptr) {

src/db/update/Queue.hxx

@@ -50,6 +50,10 @@ public:
 	bool Push(const char *path, bool discard, unsigned id);
 
 	UpdateQueueItem Pop();
+
+	void Clear() {
+		update_queue = decltype(update_queue)();
+	}
 };
 
 #endif

src/db/update/Service.cxx

@@ -47,6 +47,23 @@ UpdateService::UpdateService(EventLoop &_loop, SimpleDatabase &_db,
 {
 }
 
+UpdateService::~UpdateService()
+{
+	CancelAllAsync();
+
+	if (update_thread.IsDefined())
+		update_thread.Join();
+}
+
+void
+UpdateService::CancelAllAsync()
+{
+	assert(GetEventLoop().IsInsideOrNull());
+
+	queue.Clear();
+	walk.Cancel();
+}
+
 inline void
 UpdateService::Task()
 {
@@ -94,6 +111,8 @@ UpdateService::StartThread(UpdateQueueItem &&i)
 
 	next = std::move(i);
 
+	walk.Prepare();
+
 	Error error;
 	if (!update_thread.Start(Task, this, error))
 		FatalError(error);

src/db/update/Service.hxx

@@ -64,6 +64,8 @@ public:
 		      Storage &_storage,
 		      DatabaseListener &_listener);
 
+	~UpdateService();
+
 	/**
 	 * Returns a non-zero job id when we are currently updating
 	 * the database.
@@ -82,6 +84,12 @@ public:
 	gcc_nonnull_all
 	unsigned Enqueue(const char *path, bool discard);
 
+	/**
+	 * Clear the queue and cancel the current update.  Does not
+	 * wait for the thread to exit.
+	 */
+	void CancelAllAsync();
+
 private:
 	/* virtual methods from class DeferredMonitor */
 	virtual void RunDeferred() override;

src/db/update/Walk.cxx

@@ -358,7 +358,7 @@ UpdateWalk::UpdateDirectory(Directory &directory, const FileInfo &info)
 	PurgeDeletedFromDirectory(directory);
 
 	const char *name_utf8;
-	while ((name_utf8 = reader->Read()) != nullptr) {
+	while (!cancel && (name_utf8 = reader->Read()) != nullptr) {
 		if (skip_path(name_utf8))
 			continue;
 

src/db/update/Walk.hxx

@@ -48,6 +48,13 @@ class UpdateWalk final {
 	bool walk_discard;
 	bool modified;
 
+	/**
+	 * Set to true by the main thread when the update thread shall
+	 * cancel as quickly as possible.  Access to this flag is
+	 * unprotected.
+	 */
+	volatile bool cancel;
+
 	Storage &storage;
 
 	DatabaseEditor editor;
@@ -56,6 +63,22 @@ public:
 	UpdateWalk(EventLoop &_loop, DatabaseListener &_listener,
 		   Storage &_storage);
 
+	/**
+	 * Cancel the current update and quit the Walk() method as
+	 * soon as possible.
+	 */
+	void Cancel() {
+		cancel = true;
+	}
+
+	/**
+	 * Call from the main thread before starting the update
+	 * thread.
+	 */
+	void Prepare() {
+		cancel = false;
+	}
+
 	/**
 	 * Returns true if the database was modified.
 	 */