From a5b5328336d1d59c52bb505ed14820cdb7e14fbf Mon Sep 17 00:00:00 2001
From: Lee Howes <lwh@fb.com>
Date: Tue, 26 Dec 2017 20:11:48 -0800
Subject: [PATCH] Add getSemiFuture to folly::SharedPromise

Summary: Adds getSemiFuture functionality to folly::SharedPromise. Implements getFuture in terms of this, using folly::InlineExecutor to ensure that there is no change of behaviour.

Reviewed By: yfeldblum

Differential Revision: D6628723

fbshipit-source-id: 0ce7c7773b9290998ce87f84fa5d82ba957f0313
---
 folly/futures/SharedPromise-inl.h        |  9 +++++++--
 folly/futures/SharedPromise.h            | 10 ++++++++++
 folly/futures/test/SharedPromiseTest.cpp | 18 ++++++++++++++++++
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/folly/futures/SharedPromise-inl.h b/folly/futures/SharedPromise-inl.h
index 362736ec..3c9af5a6 100644
--- a/folly/futures/SharedPromise-inl.h
+++ b/folly/futures/SharedPromise-inl.h
@@ -54,7 +54,7 @@ size_t SharedPromise<T>::size() {
 }
 
 template <class T>
-Future<T> SharedPromise<T>::getFuture() {
+SemiFuture<T> SharedPromise<T>::getSemiFuture() {
   std::lock_guard<std::mutex> g(mutex_);
   size_++;
   if (hasValue_) {
@@ -64,10 +64,15 @@ Future<T> SharedPromise<T>::getFuture() {
     if (interruptHandler_) {
       promises_.back().setInterruptHandler(interruptHandler_);
     }
-    return promises_.back().getFuture();
+    return promises_.back().getSemiFuture();
   }
 }
 
+template <class T>
+Future<T> SharedPromise<T>::getFuture() {
+  return getSemiFuture().via(&folly::InlineExecutor::instance());
+}
+
 template <class T>
 template <class E>
 typename std::enable_if<std::is_base_of<std::exception, E>::value>::type
diff --git a/folly/futures/SharedPromise.h b/folly/futures/SharedPromise.h
index d3b363ef..70579267 100644
--- a/folly/futures/SharedPromise.h
+++ b/folly/futures/SharedPromise.h
@@ -17,6 +17,7 @@
 #pragma once
 
 #include <folly/Portability.h>
+#include <folly/executors/InlineExecutor.h>
 #include <folly/futures/Promise.h>
 
 namespace folly {
@@ -50,6 +51,15 @@ class SharedPromise {
    * Return a Future tied to the shared core state. Unlike Promise::getFuture,
    * this can be called an unlimited number of times per SharedPromise.
    */
+  SemiFuture<T> getSemiFuture();
+
+  /**
+   * Return a Future tied to the shared core state. Unlike Promise::getFuture,
+   * this can be called an unlimited number of times per SharedPromise.
+   * NOTE: This function is deprecated. Please use getSemiFuture and pass the
+   *       appropriate executor to .via on the returned SemiFuture to get a
+   *       valid Future where necessary.
+   */
   Future<T> getFuture();
 
   /** Return the number of Futures associated with this SharedPromise */
diff --git a/folly/futures/test/SharedPromiseTest.cpp b/folly/futures/test/SharedPromiseTest.cpp
index 3cb878dd..f49bdd43 100644
--- a/folly/futures/test/SharedPromiseTest.cpp
+++ b/folly/futures/test/SharedPromiseTest.cpp
@@ -19,6 +19,24 @@
 
 using namespace folly;
 
+TEST(SharedPromise, setGetSemiFuture) {
+  SharedPromise<int> p;
+  p.setValue(1);
+  auto f1 = p.getSemiFuture();
+  auto f2 = p.getSemiFuture();
+  EXPECT_EQ(1, f1.value());
+  EXPECT_EQ(1, f2.value());
+}
+
+TEST(SharedPromise, setGetMixed) {
+  SharedPromise<int> p;
+  p.setValue(1);
+  auto f1 = p.getSemiFuture();
+  auto f2 = p.getFuture();
+  EXPECT_EQ(1, f1.value());
+  EXPECT_EQ(1, f2.value());
+}
+
 TEST(SharedPromise, setGet) {
   SharedPromise<int> p;
   p.setValue(1);
-- 
2.34.1