KeepAlive via functions

Summary: Add via helpers for KeepAlive argument

Reviewed By: yfeldblum

Differential Revision: D9617303

fbshipit-source-id: 4ace3ea5f48fd8fbed70bcdf7654a1435f5e1d72

folly/futures/Future-inl.h

@@ -1309,6 +1309,12 @@ auto via(Executor* x, Func&& func) -> Future<
   return via(x).then(std::forward<Func>(func));
 }
 
+template <class Func>
+auto via(Executor::KeepAlive<> x, Func&& func) -> Future<
+    typename isFutureOrSemiFuture<decltype(std::declval<Func>()())>::Inner> {
+  return via(std::move(x)).then(std::forward<Func>(func));
+}
+
 // makeFuture
 
 template <class T>
@@ -1375,6 +1381,10 @@ Future<Unit> via(Executor* executor, int8_t priority) {
   return makeFuture().via(executor, priority);
 }
 
+Future<Unit> via(Executor::KeepAlive<> executor, int8_t priority) {
+  return makeFuture().via(std::move(executor), priority);
+}
+
 namespace futures {
 namespace detail {
 

folly/futures/helpers.h

@@ -270,6 +270,10 @@ inline Future<Unit> via(
     Executor* executor,
     int8_t priority = Executor::MID_PRI);
 
+inline Future<Unit> via(
+    Executor::KeepAlive<> executor,
+    int8_t priority = Executor::MID_PRI);
+
 /// Execute a function via the given executor and return a future.
 /// This is semantically equivalent to via(executor).then(func), but
 /// easier to read and slightly more efficient.
@@ -277,6 +281,10 @@ template <class Func>
 auto via(Executor*, Func&& func) -> Future<
     typename isFutureOrSemiFuture<decltype(std::declval<Func>()())>::Inner>;
 
+template <class Func>
+auto via(Executor::KeepAlive<>, Func&& func) -> Future<
+    typename isFutureOrSemiFuture<decltype(std::declval<Func>()())>::Inner>;
+
 /** When all the input Futures complete, the returned Future will complete.
   Errors do not cause early termination; this Future will always succeed
   after all its Futures have finished (whether successfully or with an

folly/futures/test/ViaTest.cpp

@@ -634,3 +634,13 @@ TEST(ViaFunc, moveOnly) {
 
   EXPECT_EQ(42, via(&x, [intp = std::move(intp)] { return *intp; }).getVia(&x));
 }
+
+TEST(ViaFunc, valueKeepAlive) {
+  ManualExecutor x;
+  EXPECT_EQ(42, via(getKeepAliveToken(&x), [] { return 42; }).getVia(&x));
+}
+
+TEST(ViaFunc, thenValueKeepAlive) {
+  ManualExecutor x;
+  EXPECT_EQ(42, via(getKeepAliveToken(&x)).then([] { return 42; }).getVia(&x));
+}