Enhancement: eliminate UI freeze during cloud preset sync on startup (#13673)

fix: eliminate UI freeze during cloud preset sync on startup
  Move synchronous HTTP calls off the main thread in
  GUI_App::start_sync_user_preset():

  - Call scan_orphaned_info_files() and process_delete_presets() in
    the background sync thread instead of the UI thread, so their
    HTTP DELETE calls don't block startup.
  - Call reload_settings() directly from the background thread
    instead of via CallAfter, so get_user_presets() (HTTP GET) and
    load/save_user_presets (file I/O) run off the main thread.
  - Guard update_side_preset_ui() and app_config->save() with
    is_main_thread_active() / CallAfter so they're safe when called
    from a worker thread.
  - Simplifiy finishFn lambdas: the progress-dialog case only
    destroys the dialog; the no-dialog case is a no-op.

src/libslic3r/AppConfig.cpp

@@ -834,8 +834,10 @@ std::string AppConfig::load()
 
 void AppConfig::save()
 {
-    if (! is_main_thread_active())
+    if (!is_main_thread_active()) {
+        BOOST_LOG_TRIVIAL(fatal) << "Calling AppConfig::save() from a worker thread!";
         throw CriticalException("Calling AppConfig::save() from a worker thread!");
+    }
 
     // The config is first written to a file with a PID suffix and then moved
     // to avoid race conditions with multiple instances of Slic3r

src/slic3r/GUI/GUI_App.cpp

@@ -5782,7 +5782,10 @@ void GUI_App::reload_settings()
         load_pending_vendors();
         preset_bundle->load_user_presets(*app_config, user_presets, ForwardCompatibilitySubstitutionRule::Enable);
         preset_bundle->save_user_presets(*app_config, get_delete_cache_presets());
-        mainframe->update_side_preset_ui();
+        if (is_main_thread_active())
+            mainframe->update_side_preset_ui();
+        else
+            CallAfter([this] { mainframe->update_side_preset_ui(); });
     }
 }
 
@@ -6023,8 +6026,10 @@ void GUI_App::load_pending_vendors()
         return;
 
     preset_bundle->apply_vendor_config(need_add_vendors, need_add_filaments, app_config, false);
-    app_config->save();
-
+    if (is_main_thread_active())
+        app_config->save();
+    else
+        CallAfter([this] { app_config->save(); });
     need_add_vendors.clear();
     need_add_filaments.clear();
 }
@@ -6508,36 +6513,29 @@ void GUI_App::start_sync_user_preset(bool with_progress_dlg)
         cancelFn = [this, dlg]() {
             return is_closing() || dlg->WasCanceled();
         };
-        finishFn = [this, userid = m_agent->get_user_id(), dlg, t = std::weak_ptr<int>(m_user_sync_token)](bool ok) {
-            CallAfter([=]{
-                dlg->Destroy();
-                if (ok && m_agent && t.lock() == m_user_sync_token && userid == m_agent->get_user_id()) reload_settings();
-            });
+        finishFn = [this, dlg](bool) {
+            CallAfter([=]{ dlg->Destroy(); });
         };
     }
     else {
-        finishFn = [this, userid = m_agent->get_user_id(), t = std::weak_ptr<int>(m_user_sync_token)](bool ok) {
-            CallAfter([=] {
-                if (ok && m_agent && t.lock() == m_user_sync_token && userid == m_agent->get_user_id()) reload_settings();
-            });
-        };
+        finishFn = [](bool) {}; // reload_settings() is now triggered from the background thread
         cancelFn = [this]() {
             return is_closing();
         };
     }
 
-    // Do a one-time scan for files that may be pending deletion (e.g., was deleted while not connected to internet)
-    // Scan for orphaned .info files on startup and add them to deletion queue
-    scan_orphaned_info_files();
-    process_delete_presets();
-
     Bind(EVT_UPDATE_PRESET_BUNDLE,&GUI_App::update_single_bundle,this);
 
     m_sync_update_thread = Slic3r::create_thread(
         [this, progressFn, cancelFn, finishFn, t = std::weak_ptr<int>(m_user_sync_token)] {
+            if (!m_agent) return;
+
+            // One-time scan for orphaned .info files left over from offline deletions; queues HTTP DELETEs.
+            scan_orphaned_info_files();
+            process_delete_presets();
+
             // get setting list, update setting list
             std::string version = preset_bundle->get_vendor_profile_version(PresetBundle::ORCA_DEFAULT_BUNDLE).to_string();
-            if(!m_agent) return;
 
             // run check_and_fix_user_presets_syncinfo once before syncing to make sure all presets have correct sync_info
             // So that we can sync presets that are migrated from old version or users manually put preset files in preset folder
@@ -6562,9 +6560,12 @@ void GUI_App::start_sync_user_preset(bool with_progress_dlg)
                 }
             }, progressFn, cancelFn);
             BOOST_LOG_TRIVIAL(info) << __FUNCTION__ << __LINE__ << " get_setting_list2 ret = " << ret << " m_is_closing = " << m_is_closing;
-            
+
             finishFn(ret == 0);
 
+            if (ret == 0 && m_agent && !t.expired())
+                reload_settings();
+
             // For orca specific syncing
             auto orca_agent = std::dynamic_pointer_cast<OrcaCloudServiceAgent>(m_agent->get_cloud_agent());
             int tick_tock = -1, sync_count = 0; // tick_tock = -1 to immediately run sync the frist time this thread runs