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, 136 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/asset_library_service.cc b/source/blender/blenkernel/intern/asset_library_service.cc
new file mode 100644
index 00000000000..14604def0d3
--- /dev/null
+++ b/source/blender/blenkernel/intern/asset_library_service.cc
@@ -0,0 +1,136 @@
+/*
+ * 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
+ */
+
+#include "asset_library_service.hh"
+
+#include "BKE_asset_library.hh"
+#include "BKE_blender.h"
+#include "BKE_callbacks.h"
+
+#include "BLI_string_ref.hh"
+
+#include "MEM_guardedalloc.h"
+
+#include "CLG_log.h"
+
+static CLG_LogRef LOG = {"bke.asset_service"};
+
+namespace blender::bke {
+
+std::unique_ptr<AssetLibraryService> AssetLibraryService::instance_;
+bool AssetLibraryService::atexit_handler_registered_ = false;
+
+AssetLibraryService *AssetLibraryService::get()
+{
+  if (!instance_) {
+    allocate_service_instance();
+  }
+  return instance_.get();
+}
+
+void AssetLibraryService::destroy()
+{
+  if (!instance_) {
+    return;
+  }
+  instance_->app_handler_unregister();
+  instance_.reset();
+}
+
+AssetLibrary *AssetLibraryService::get_asset_library_on_disk(StringRefNull top_level_directory)
+{
+  BLI_assert_msg(!top_level_directory.is_empty(),
+                 "top level directory must be given for on-disk asset library");
+
+  AssetLibraryPtr *lib_uptr_ptr = on_disk_libraries_.lookup_ptr(top_level_directory);
+  if (lib_uptr_ptr != nullptr) {
+    CLOG_INFO(&LOG, 2, "get \"%s\" (cached)", top_level_directory.c_str());
+    return lib_uptr_ptr->get();
+  }
+
+  AssetLibraryPtr lib_uptr = std::make_unique<AssetLibrary>();
+  AssetLibrary *lib = lib_uptr.get();
+
+  lib->on_save_handler_register();
+  lib->load(top_level_directory);
+
+  on_disk_libraries_.add_new(top_level_directory, std::move(lib_uptr));
+  CLOG_INFO(&LOG, 2, "get \"%s\" (loaded)", top_level_directory.c_str());
+  return lib;
+}
+
+AssetLibrary *AssetLibraryService::get_asset_library_current_file()
+{
+  if (current_file_library_) {
+    CLOG_INFO(&LOG, 2, "get current file lib (cached)");
+  }
+  else {
+    CLOG_INFO(&LOG, 2, "get current file lib (loaded)");
+    current_file_library_ = std::make_unique<AssetLibrary>();
+    current_file_library_->on_save_handler_register();
+  }
+
+  AssetLibrary *lib = current_file_library_.get();
+  return lib;
+}
+
+void AssetLibraryService::allocate_service_instance()
+{
+  instance_ = std::make_unique<AssetLibraryService>();
+  instance_->app_handler_register();
+
+  if (!atexit_handler_registered_) {
+    /* Ensure the instance gets freed before Blender's memory leak detector runs. */
+    BKE_blender_atexit_register([](void * /*user_data*/) { AssetLibraryService::destroy(); },
+                                nullptr);
+    atexit_handler_registered_ = true;
+  }
+}
+
+static void on_blendfile_load(struct Main * /*bMain*/,
+                              struct PointerRNA ** /*pointers*/,
+                              const int /*num_pointers*/,
+                              void * /*arg*/)
+{
+  AssetLibraryService::destroy();
+}
+
+/**
+ * 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 AssetLibraryService::app_handler_register()
+{
+  /* The callback system doesn't own `on_load_callback_store_`. */
+  on_load_callback_store_.alloc = false;
+
+  on_load_callback_store_.func = &on_blendfile_load;
+  on_load_callback_store_.arg = this;
+
+  BKE_callback_add(&on_load_callback_store_, BKE_CB_EVT_LOAD_PRE);
+}
+
+void AssetLibraryService::app_handler_unregister()
+{
+  BKE_callback_remove(&on_load_callback_store_, BKE_CB_EVT_LOAD_PRE);
+  on_load_callback_store_.func = nullptr;
+  on_load_callback_store_.arg = nullptr;
+}
+
+}  // namespace blender::bke