4 files changed, 49 insertions, 3 deletions
diff --git a/src/util/asyncMemo.ts b/src/util/asyncMemo.ts
index 8b7b1c9bb..34868ab4f 100644
--- a/src/util/asyncMemo.ts
+++ b/src/util/asyncMemo.ts
@@ -21,8 +21,8 @@ export interface MemoEntry<T> {
 }
 
 export class AsyncOpMemo<T> {
-  n = 0;
-  memo: { [k: string]: MemoEntry<T> } = {};
+  private n = 0;
+  private memo: { [k: string]: MemoEntry<T> } = {};
   put(key: string, p: Promise<T>): Promise<T> {
     const n = this.n++;
     this.memo[key] = {
diff --git a/src/util/promiseUtils.ts b/src/util/promiseUtils.ts
index eb649471b..9add2c407 100644
--- a/src/util/promiseUtils.ts
+++ b/src/util/promiseUtils.ts
@@ -36,4 +36,25 @@ export function openPromise<T>(): OpenedPromise<T> {
     throw Error();
   }
   return { resolve, reject, promise };
+}
+
+export class AsyncCondition {
+  private _waitPromise: Promise<void>;
+  private _resolveWaitPromise: (val: void) => void;
+  constructor() {
+    const op = openPromise<void>();
+    this._waitPromise = op.promise;
+    this._resolveWaitPromise = op.resolve;
+  }
+
+  wait(): Promise<void> {
+    return this._waitPromise;
+  }
+
+  trigger(): void {
+    this._resolveWaitPromise();
+    const op = openPromise<void>();
+    this._waitPromise = op.promise;
+    this._resolveWaitPromise = op.resolve;
+  }
 }
 \ No newline at end of file
diff --git a/src/util/query.ts b/src/util/query.ts
index 5726bcaa6..6942d471e 100644
--- a/src/util/query.ts
+++ b/src/util/query.ts
@@ -351,15 +351,32 @@ class TransactionHandle {
   }
 }
 
+export function runWithReadTransaction<T>(
+  db: IDBDatabase,
+  stores: Store<any>[],
+  f: (t: TransactionHandle) => Promise<T>,
+): Promise<T> {
+  return runWithTransaction<T>(db, stores, f, "readonly");
+}
+
 export function runWithWriteTransaction<T>(
   db: IDBDatabase,
   stores: Store<any>[],
   f: (t: TransactionHandle) => Promise<T>,
 ): Promise<T> {
+  return runWithTransaction<T>(db, stores, f, "readwrite");
+}
+
+function runWithTransaction<T>(
+  db: IDBDatabase,
+  stores: Store<any>[],
+  f: (t: TransactionHandle) => Promise<T>,
+  mode: "readonly" | "readwrite",
+): Promise<T> {
   const stack = Error("Failed transaction was started here.");
   return new Promise((resolve, reject) => {
     const storeName = stores.map(x => x.name);
-    const tx = db.transaction(storeName, "readwrite");
+    const tx = db.transaction(storeName, mode);
     let funResult: any = undefined;
     let gotFunResult: boolean = false;
     tx.oncomplete = () => {
diff --git a/src/util/timer.ts b/src/util/timer.ts
index d3bb5d485..865c17faf 100644
--- a/src/util/timer.ts
+++ b/src/util/timer.ts
@@ -105,6 +105,14 @@ export class TimerGroup {
     }
   }
 
+  resolveAfter(delayMs: number): Promise<void> {
+    return new Promise<void>((resolve, reject) => {
+      this.after(delayMs, () => {
+        resolve();
+      });
+    });
+  }
+
   after(delayMs: number, callback: () => void): TimerHandle {
     if (this.stopped) {
       console.warn("dropping timer since timer group is stopped");