async::promiseWait

Summary:
Provide an Async wrapper for fibers::await, which blocks current task until promise is fulfilled.
This isn't a build block that is used in very common scenario, so prefered to put it in its own file.

Differential Revision: D22135318

fbshipit-source-id: 753dbefc4ac9a907f5b1f656f70291c88187b5e8

folly/fibers/async/Promise.h

+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <folly/fibers/async/Async.h>
+
+namespace folly {
+namespace fibers {
+namespace async {
+
+/**
+ * Async annotated wrapper around fibers::await
+ */
+template <typename F>
+auto promiseWait(F&& func) {
+  // Call into blocking API
+  return Async{folly::fibers::await(std::forward<F>(func))};
+}
+
+} // namespace async
+} // namespace fibers
+} // namespace folly

folly/fibers/async/test/AsyncTest.cpp

@@ -21,6 +21,7 @@
 #include <folly/fibers/async/Async.h>
 #include <folly/fibers/async/Baton.h>
 #include <folly/fibers/async/Future.h>
+#include <folly/fibers/async/Promise.h>
 #include <folly/io/async/EventBase.h>
 
 #if FOLLY_HAS_COROUTINES
@@ -114,6 +115,18 @@ TEST(AsyncTest, asyncBaton) {
           .getVia(&evb));
 }
 
+TEST(AsyncTest, asyncPromise) {
+  folly::EventBase evb;
+  auto& fm = getFiberManager(evb);
+
+  fm.addTaskFuture([&]() {
+      auto res = async::await(
+          async::promiseWait([](Promise<int> p) { p.setValue(42); }));
+      EXPECT_EQ(res, 42);
+    })
+      .getVia(&evb);
+}
+
 TEST(AsyncTest, asyncFuture) {
   folly::EventBase evb;
   auto& fm = getFiberManager(evb);