Defer terminal IndexedDB close behind storage flush (#886)

Author: wieslawsoltes

docs/validation/terminal-cancelled-storage-flush-884.md

@@ -32,6 +32,13 @@ lifecycle event returns. WebScene consequently removed the only task that
 could start the IndexedDB write and observed no terminal persistence work, so
 `pagehide` and reload handoff proceeded immediately.
 
+After retaining that callback, repeated installed-package runs exposed the
+second half of the shutdown race. VS Code also closes its storage database from
+a shutdown microtask before the retained timer starts. One run passed in
+16.204 seconds, while the next failed in 25.623 seconds with the key present
+before reload and absent after reopening; the failed log reported that
+`vscode-web-db` was closed.
+
 A focused native fixture reproduces the exact order. Before the fix it reports:
 
 ```text
@@ -49,6 +56,12 @@ WebScene retains the accepted callback privately until the handoff boundary.
 Its microtasks, zero-delay descendants, and IndexedDB operations inherit the
 same bounded terminal ancestry.
 
+If `IDBDatabase.close()` runs from that same lifecycle turn while accepted
+terminal persistence remains, the compatibility layer queues the close behind
+the retained flush. The database still closes before `pagehide` and host
+handoff. Calls made outside this narrow terminal condition keep synchronous
+close semantics.
+
 This terminal-only durability rule is intentionally narrower than ordinary
 timer cancellation. Timers created outside terminal lifecycle, delayed timers,
 intervals, animation frames, and work beyond the 1,024-task budget keep their
@@ -65,7 +78,8 @@ WEBSCENE_NATIVE_ENGINE_TEST_FILTER=terminal-indexeddb-navigation \
 ```
 
 Result on macOS arm64 Release: pass. The durable transaction-to-handoff gate
-completed in 0.0036 seconds. The fixture also covers restart durability,
+completed in 0.0037 seconds. The fixture also covers a shutdown-microtask
+database close before the retained flush, restart durability,
 pre-existing IndexedDB work, exact lifecycle order, ordinary cancellation,
 future timers, intervals, native completion descendants, and the bounded
 self-refilling-task ceiling.

experiments/WebScene.NativeEngine.Probe/native/webscene_indexeddb_compatibility.h

@@ -9,7 +9,9 @@ inline constexpr std::string_view indexeddb_compatibility_source = R"JS(
   'use strict';
   const nativeStorage = globalThis.__webSceneIndexedDBStorage;
   const scheduleTask = globalThis.__webSceneIndexedDBTask;
-  if (typeof nativeStorage !== 'function' || typeof scheduleTask !== 'function') return;
+  const shouldDeferClose = globalThis.__webSceneIndexedDBShouldDeferClose;
+  if (typeof nativeStorage !== 'function' || typeof scheduleTask !== 'function'
+      || typeof shouldDeferClose !== 'function') return;
   const openConnections = new Map();
   const loadedDatabases = new Map();
   const writeTails = new Map();
@@ -375,6 +377,7 @@ R"JS(  class IDBTransaction extends EventTarget {
       this._state = state;
       this._revision = revision;
       this._closed = false;
+      this._terminalClosePending = false;
       this._upgradeTransaction = null;
       this.onabort = null;
       this.onerror = null;
@@ -421,6 +424,15 @@ R"JS(  class IDBTransaction extends EventTarget {
     }
     close() {
       if (this._closed) return;
+      if (shouldDeferClose()) {
+        if (this._terminalClosePending) return;
+        this._terminalClosePending = true;
+        scheduleTask(() => {
+          this._terminalClosePending = false;
+          this.close();
+        });
+        return;
+      }
       this._closed = true;
       openConnections.get(this.name)?.delete(this);
     }

experiments/WebScene.NativeEngine.Probe/native/webscene_v8_runtime_indexeddb.inc

@@ -603,6 +603,17 @@
         schedule_timer(info, false, true);
     }
 
+    static void indexeddb_should_defer_close(
+        const v8::FunctionCallbackInfo<v8::Value>& info)
+    {
+        auto* self = current(info.GetIsolate());
+        info.GetReturnValue().Set(v8::Boolean::New(
+            info.GetIsolate(),
+            self != nullptr
+                && self->window_close_lifecycle_dispatching
+                && self->has_terminal_handoff_persistence_work()));
+    }
+
     void install_indexeddb(v8::Local<v8::Context> realm)
     {
         if (indexeddb == nullptr) return;
@@ -617,6 +628,11 @@
             js_string(isolate, "__webSceneIndexedDBTask"),
             v8::Function::New(realm, indexeddb_schedule_task).ToLocalChecked(),
             v8::PropertyAttribute::DontEnum).Check();
+        global->DefineOwnProperty(
+            realm,
+            js_string(isolate, "__webSceneIndexedDBShouldDeferClose"),
+            v8::Function::New(realm, indexeddb_should_defer_close).ToLocalChecked(),
+            v8::PropertyAttribute::DontEnum).Check();
         auto script = v8::Script::Compile(
             realm,
             js_string(isolate, std::string(indexeddb_compatibility_source).c_str()))

experiments/WebScene.NativeEngine.Probe/tests/native_v8_runtime_indexeddb_tests.inc

@@ -679,6 +679,12 @@ void test_terminal_navigation_waits_for_indexeddb_commit()
             };
           }, 0);
           clearTimeout(pendingFlushTimer);
+          // Browser workbench disposal closes its storage database from the
+          // same shutdown turn before the retained callback starts.
+          Promise.resolve().then(() => {
+            terminalIndexedDb.order.push('close-request');
+            database.close();
+          });
         });
         addEventListener('pagehide', () => {
           terminalIndexedDb.order.push('pagehide');
@@ -732,8 +738,10 @@ void test_terminal_navigation_waits_for_indexeddb_commit()
             "&&terminalIndexedDb.continuation===true"
             "&&!terminalIndexedDb.ordinaryCancelFired"
             "&&terminalIndexedDb.order[0]==='beforeunload'"
+            "&&terminalIndexedDb.order.indexOf('close-request')>0"
             "&&terminalIndexedDb.order.indexOf('preexisting-commit')>0"
-            "&&terminalIndexedDb.order.indexOf('flush-timer')>0"
+            "&&terminalIndexedDb.order.indexOf('flush-timer')>"
+                "terminalIndexedDb.order.indexOf('close-request')"
             "&&terminalIndexedDb.order.indexOf('commit')>"
                 "terminalIndexedDb.order.indexOf('flush-timer')"
             "&&terminalIndexedDb.order.indexOf('continuation')>"