Future: some fixes re: handling of universal references

[folly.git] / folly / futures / helpers.h

diff --git a/folly/futures/helpers.h b/folly/futures/helpers.h
index ea1dc70d8aec4c4225335dcf538e503031c89cce..26187b8fa0662316bf66ca97471edb7c3364c854 100644 (file)
--- a/folly/futures/helpers.h
+++ b/folly/futures/helpers.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 #pragma once
 
 #include <folly/futures/Future.h>
+#include <folly/Portability.h>
 
 namespace folly {
 
@@ -74,18 +75,44 @@ Future<typename std::decay<T>::type> makeFuture(T&& t);
 /** Make a completed void Future. */
 Future<Unit> makeFuture();
 
-/** Make a completed Future by executing a function. If the function throws
-  we capture the exception, otherwise we capture the result. */
+/**
+  Make a Future by executing a function.
+
+  If the function returns a value of type T, makeFutureWith
+  returns a completed Future<T>, capturing the value returned
+  by the function.
+
+  If the function returns a Future<T> already, makeFutureWith
+  returns just that.
+
+  Either way, if the function throws, a failed Future is
+  returned that captures the exception.
+
+  Calling makeFutureWith(func) is equivalent to calling
+  makeFuture().then(func).
+*/
+
+// makeFutureWith(Future<T>()) -> Future<T>
+template <class F>
+typename std::enable_if<isFuture<typename std::result_of<F()>::type>::value,
+                        typename std::result_of<F()>::type>::type
+makeFutureWith(F&& func);
+
+// makeFutureWith(T()) -> Future<T>
+// makeFutureWith(void()) -> Future<Unit>
 template <class F>
-auto makeFutureWith(F&& func)
-    -> Future<typename Unit::Lift<decltype(func())>::type>;
+typename std::enable_if<
+    !(isFuture<typename std::result_of<F()>::type>::value),
+    Future<typename Unit::Lift<typename std::result_of<F()>::type>::type>>::type
+makeFutureWith(F&& func);
 
 /// Make a failed Future from an exception_ptr.
 /// Because the Future's type cannot be inferred you have to specify it, e.g.
 ///
 ///   auto f = makeFuture<string>(std::current_exception());
 template <class T>
-DEPRECATED Future<T> makeFuture(std::exception_ptr const& e);
+FOLLY_DEPRECATED("use makeFuture(exception_wrapper)")
+Future<T> makeFuture(std::exception_ptr const& e);
 
 /// Make a failed Future from an exception_wrapper.
 template <class T>
@@ -120,8 +147,8 @@ inline Future<Unit> via(
 /// This is semantically equivalent to via(executor).then(func), but
 /// easier to read and slightly more efficient.
 template <class Func>
-auto via(Executor*, Func func)
-  -> Future<typename isFuture<decltype(func())>::Inner>;
+auto via(Executor*, Func&& func)
+    -> Future<typename isFuture<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
@@ -199,6 +226,23 @@ auto collectAny(Collection&& c) -> decltype(collectAny(c.begin(), c.end())) {
   return collectAny(c.begin(), c.end());
 }
 
+/** Similar to collectAny, collectAnyWithoutException return the first Future to
+ * complete without exceptions. If none of the future complete without
+ * excpetions, the last exception will be returned as a result.
+  */
+template <class InputIterator>
+Future<std::pair<
+    size_t,
+    typename std::iterator_traits<InputIterator>::value_type::value_type>>
+collectAnyWithoutException(InputIterator first, InputIterator last);
+
+/// Sugar for the most common case
+template <class Collection>
+auto collectAnyWithoutException(Collection&& c)
+    -> decltype(collectAnyWithoutException(c.begin(), c.end())) {
+  return collectAnyWithoutException(c.begin(), c.end());
+}
+
 /** when n Futures have completed, the Future completes with a vector of
   the index and Try of those n Futures (the indices refer to the original
   order, but the result vector will be in an arbitrary order)
@@ -319,6 +363,9 @@ namespace futures {
  *  indicating that the failure was transitory.
  *
  *  Cancellation is not supported.
+ *
+ *  If both FF and Policy inline executes, then it is possible to hit a stack
+ *  overflow due to the recursive nature of the retry implementation
  */
 template <class Policy, class FF>
 typename std::result_of<FF(size_t)>::type
@@ -340,7 +387,7 @@ retryingPolicyCappedJitteredExponentialBackoff(
     Duration backoff_min,
     Duration backoff_max,
     double jitter_param,
-    URNG rng,
+    URNG&& rng,
     Policy&& p);
 
 inline