Assets: add global `bke::AssetLibraryService` class

Add `blender::bke::AssetLibraryService` class that acts like a
blendfile-scoped singleton. It's allocated upon the first call to
`BKE_asset_library_load` and destroyed in the LOAD-PRE handler.

The `AssetLibraryService` ensures that edits to asset catalogs are not
lost when the asset browser editor closes (or even reloads). Instead,
the `AssetLibrary` pointers it owns are kept around as long as the blend
file is open.

Reviewed By: Severin

Maniphest Tasks: T92151

Differential Revision: https://developer.blender.org/D12885

1 files changed, 90 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/asset_library_service.hh b/source/blender/blenkernel/intern/asset_library_service.hh
new file mode 100644
index 00000000000..63ffe56ab74
--- /dev/null
+++ b/source/blender/blenkernel/intern/asset_library_service.hh
@@ -0,0 +1,90 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup bke
+ */
+
+#pragma once
+
+#ifndef __cplusplus
+#  error This is a C++-only header file.
+#endif
+
+#include "BKE_asset_library.hh"
+
+#include "BLI_map.hh"
+
+#include <memory>
+
+namespace blender::bke {
+
+/**
+ * Global singleton-ish that provides access to individual #AssetLibrary instances.
+ *
+ * Whenever a blend file is loaded, the existing instance of AssetLibraryService is destructed, and
+ * a new one is created -- hence the "singleton-ish". This ensures only information about relevant
+ * asset libraries is loaded.
+ *
+ * \note How Asset libraries are identified may change in the future.
+ *  For now they are assumed to be:
+ * - on disk (identified by the absolute directory), or
+ * - the "current file" library (which is in memory but could have catalogs
+ *   loaded from a file on disk).
+ */
+class AssetLibraryService {
+ public:
+  using AssetLibraryPtr = std::unique_ptr<AssetLibrary>;
+
+  AssetLibraryService() = default;
+  ~AssetLibraryService() = default;
+
+  /** Return the AssetLibraryService singleton, allocating it if necessary. */
+  static AssetLibraryService *get();
+
+  /** Destroy the AssetLibraryService singleton. It will be reallocated by #get() if necessary. */
+  static void destroy();
+
+  /**
+   * Get the given asset library. Opens it (i.e. creates a new AssetLibrary instance) if necessary.
+   */
+  AssetLibrary *get_asset_library_on_disk(StringRefNull top_level_directory);
+
+  /** Get the "Current File" asset library. */
+  AssetLibrary *get_asset_library_current_file();
+
+ protected:
+  static std::unique_ptr<AssetLibraryService> instance_;
+
+  /* Mapping absolute path of the library's top-level directory to the AssetLibrary instance. */
+  Map<std::string, AssetLibraryPtr> on_disk_libraries_;
+  AssetLibraryPtr current_file_library_;
+
+  /* Handlers for managing the life cycle of the AssetLibraryService instance. */
+  bCallbackFuncStore on_load_callback_store_;
+  static bool atexit_handler_registered_;
+
+  /** Allocate a new instance of the service and assign it to `instance_`. */
+  static void allocate_service_instance();
+
+  /**
+   * Ensure the AssetLibraryService instance is destroyed before a new blend file is loaded.
+   * This makes memory management simple, and ensures a fresh start for every blend file. */
+  void app_handler_register();
+  void app_handler_unregister();
+};
+
+}  // namespace blender::bke