feat: Add ParallelHandler.

src/index.ts

@@ -189,6 +189,7 @@ export * from './util/errors/UnsupportedMediaTypeHttpError';
 
 // Util/Handlers
 export * from './util/handlers/AsyncHandler';
+export * from './util/handlers/ParallelHandler';
 export * from './util/handlers/SequenceHandler';
 export * from './util/handlers/UnsupportedAsyncHandler';
 export * from './util/handlers/WaterfallHandler';

src/util/handlers/ParallelHandler.ts

@@ -0,0 +1,23 @@
+import { AsyncHandler } from './AsyncHandler';
+
+/**
+ * A composite handler that executes handlers in parallel.
+ */
+export class ParallelHandler<TIn = void, TOut = void> extends AsyncHandler<TIn, TOut[]> {
+  private readonly handlers: AsyncHandler<TIn, TOut>[];
+
+  public constructor(handlers: AsyncHandler<TIn, TOut>[]) {
+    super();
+    this.handlers = [ ...handlers ];
+  }
+
+  public async canHandle(input: TIn): Promise<void> {
+    // eslint-disable-next-line @typescript-eslint/promise-function-async
+    await Promise.all(this.handlers.map((handler): Promise<void> => handler.canHandle(input)));
+  }
+
+  public async handle(input: TIn): Promise<TOut[]> {
+    // eslint-disable-next-line @typescript-eslint/promise-function-async
+    return Promise.all(this.handlers.map((handler): Promise<TOut> => handler.handle(input)));
+  }
+}