From 93fb2f4ea4d2cffd5ce3617a2795958329a65630 Mon Sep 17 00:00:00 2001
From: jrandolf <101637635+jrandolf@users.noreply.github.com>
Date: Tue, 9 Jan 2024 11:40:26 +0100
Subject: [PATCH] refactor: make `Deferred.valueOrThrow` idempotent. (#11657)

---
 packages/puppeteer-core/src/util/Deferred.ts | 131 ++++++++++---------
 1 file changed, 69 insertions(+), 62 deletions(-)

diff --git a/packages/puppeteer-core/src/util/Deferred.ts b/packages/puppeteer-core/src/util/Deferred.ts
index a512a928728..0dfb013bb3f 100644
--- a/packages/puppeteer-core/src/util/Deferred.ts
+++ b/packages/puppeteer-core/src/util/Deferred.ts
@@ -18,70 +18,9 @@ export interface DeferredOptions {
  * @internal
  */
 export class Deferred<T, V extends Error = Error> {
-  #isResolved = false;
-  #isRejected = false;
-  #value: T | V | TimeoutError | undefined;
-  #resolver: (value: void) => void = () => {};
-  #taskPromise = new Promise<void>(resolve => {
-    this.#resolver = resolve;
-  });
-  #timeoutId: ReturnType<typeof setTimeout> | undefined;
-  #timeoutError: TimeoutError | undefined;
-
-  constructor(opts?: DeferredOptions) {
-    if (opts && opts.timeout > 0) {
-      this.#timeoutError = new TimeoutError(opts.message);
-      this.#timeoutId = setTimeout(() => {
-        this.reject(this.#timeoutError!);
-      }, opts.timeout);
-    }
-  }
-
-  #finish(value: T | V | TimeoutError) {
-    clearTimeout(this.#timeoutId);
-    this.#value = value;
-    this.#resolver();
-  }
-
-  resolve(value: T): void {
-    if (this.#isRejected || this.#isResolved) {
-      return;
-    }
-    this.#isResolved = true;
-    this.#finish(value);
-  }
-
-  reject(error: V | TimeoutError): void {
-    if (this.#isRejected || this.#isResolved) {
-      return;
-    }
-    this.#isRejected = true;
-    this.#finish(error);
-  }
-
-  resolved(): boolean {
-    return this.#isResolved;
-  }
-
-  finished(): boolean {
-    return this.#isResolved || this.#isRejected;
-  }
-
-  value(): T | V | TimeoutError | undefined {
-    return this.#value;
-  }
-
-  async valueOrThrow(): Promise<T> {
-    await this.#taskPromise;
-    if (this.#isRejected) {
-      throw this.#value;
-    }
-    return this.#value as T;
-  }
-
   static create<R, X extends Error = Error>(
     opts?: DeferredOptions
-  ): Deferred<R> {
+  ): Deferred<R, X> {
     return new Deferred<R, X>(opts);
   }
 
@@ -112,4 +51,72 @@ export class Deferred<T, V extends Error = Error> {
       }
     }
   }
+
+  #isResolved = false;
+  #isRejected = false;
+  #value: T | V | TimeoutError | undefined;
+  // SAFETY: This is ensured by #taskPromise.
+  #resolve!: (value: void) => void;
+  #taskPromise = new Promise<void>(resolve => {
+    this.#resolve = resolve;
+  });
+  #timeoutId: ReturnType<typeof setTimeout> | undefined;
+  #timeoutError: TimeoutError | undefined;
+
+  constructor(opts?: DeferredOptions) {
+    if (opts && opts.timeout > 0) {
+      this.#timeoutError = new TimeoutError(opts.message);
+      this.#timeoutId = setTimeout(() => {
+        this.reject(this.#timeoutError!);
+      }, opts.timeout);
+    }
+  }
+
+  #finish(value: T | V | TimeoutError) {
+    clearTimeout(this.#timeoutId);
+    this.#value = value;
+    this.#resolve();
+  }
+
+  resolve(value: T): void {
+    if (this.#isRejected || this.#isResolved) {
+      return;
+    }
+    this.#isResolved = true;
+    this.#finish(value);
+  }
+
+  reject(error: V | TimeoutError): void {
+    if (this.#isRejected || this.#isResolved) {
+      return;
+    }
+    this.#isRejected = true;
+    this.#finish(error);
+  }
+
+  resolved(): boolean {
+    return this.#isResolved;
+  }
+
+  finished(): boolean {
+    return this.#isResolved || this.#isRejected;
+  }
+
+  value(): T | V | TimeoutError | undefined {
+    return this.#value;
+  }
+
+  #promise: Promise<T> | undefined;
+  valueOrThrow(): Promise<T> {
+    if (!this.#promise) {
+      this.#promise = (async () => {
+        await this.#taskPromise;
+        if (this.#isRejected) {
+          throw this.#value;
+        }
+        return this.#value as T;
+      })();
+    }
+    return this.#promise;
+  }
 }