Don't dispose the CancellationTokenSource until all onCancellationRequested handlers have run

src/vs/base/common/async.ts

@@ -28,7 +28,6 @@ export function createCancelablePromise<T>(callback: (token: CancellationToken)
 	const promise = new Promise<T>((resolve, reject) => {
 		const subscription = source.token.onCancellationRequested(() => {
 			subscription.dispose();
-			source.dispose();
 			reject(new CancellationError());
 		});
 		Promise.resolve(thenable).then(value => {
@@ -45,6 +44,7 @@ export function createCancelablePromise<T>(callback: (token: CancellationToken)
 	return <CancelablePromise<T>>new class {
 		cancel() {
 			source.cancel();
+			source.dispose();
 		}
 		then<TResult1 = T, TResult2 = never>(resolve?: ((value: T) => TResult1 | Promise<TResult1>) | undefined | null, reject?: ((reason: any) => TResult2 | Promise<TResult2>) | undefined | null): Promise<TResult1 | TResult2> {
 			return promise.then(resolve, reject);

src/vs/base/test/common/async.test.ts

@@ -93,6 +93,27 @@ suite('Async', () => {
 			return promise.then(() => assert.deepStrictEqual(order, ['in callback', 'afterCreate', 'cancelled', 'afterCancel', 'finally']));
 		});
 
+		test('execution order (async with late listener)', async function () {
+			const order: string[] = [];
+
+			const cancellablePromise = async.createCancelablePromise(async token => {
+				order.push('in callback');
+
+				await async.timeout(0);
+				store.add(token.onCancellationRequested(_ => order.push('cancelled')));
+				cancellablePromise.cancel();
+				order.push('afterCancel');
+			});
+
+			order.push('afterCreate');
+
+			const promise = cancellablePromise
+				.then(undefined, err => null)
+				.then(() => order.push('finally'));
+
+			return promise.then(() => assert.deepStrictEqual(order, ['in callback', 'afterCreate', 'cancelled', 'afterCancel', 'finally']));
+		});
+
 		test('get inner result', async function () {
 			const promise = async.createCancelablePromise(token => {
 				return async.timeout(12).then(_ => 1234);