feat: add member cache; handle all role changes with RoleManagerPlugin; exit gracefully

backend/src/Blocker.ts

@@ -0,0 +1,40 @@
+export type Block = {
+  count: number;
+  unblock: () => void;
+  getPromise: () => Promise<void>;
+};
+
+export class Blocker {
+  #blocks: Map<string, Block> = new Map();
+
+  block(key: string): void {
+    if (!this.#blocks.has(key)) {
+      const promise = new Promise<void>((resolve) => {
+        this.#blocks.set(key, {
+          count: 0, // Incremented to 1 further below
+          unblock() {
+            this.count--;
+            if (this.count === 0) {
+              resolve();
+            }
+          },
+          getPromise: () => promise, // :d
+        });
+      });
+    }
+    this.#blocks.get(key)!.count++;
+  }
+
+  unblock(key: string): void {
+    if (this.#blocks.has(key)) {
+      this.#blocks.get(key)!.unblock();
+    }
+  }
+
+  async waitToBeUnblocked(key: string): Promise<void> {
+    if (!this.#blocks.has(key)) {
+      return;
+    }
+    await this.#blocks.get(key)!.getPromise();
+  }
+}