X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/a15797ea55151ddfdbae48147e74159efe01b411..bd11885138355943e56e13d03850740ea2bcabd7:/include/xbt/future.hpp

diff --git a/include/xbt/future.hpp b/include/xbt/future.hpp
index d5a31a55ce..4d2842fca0 100644
--- a/include/xbt/future.hpp
+++ b/include/xbt/future.hpp
@@ -1,4 +1,4 @@
-/* Copyright (c) 2015-2016. The SimGrid Team.
+/* Copyright (c) 2015-2019. The SimGrid Team.
  * All rights reserved.                                                     */
 
 /* This program is free software; you can redistribute it and/or modify it
@@ -7,42 +7,155 @@
 #ifndef XBT_FUTURE_HPP
 #define XBT_FUTURE_HPP
 
-#include <future>
-#include <utility>
+#include <cstddef>
+
+#include <boost/variant.hpp>
 #include <exception>
+#include <functional>
+#include <future> // std::future_error
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
+#include <xbt/ex.h>
 
 namespace simgrid {
 namespace xbt {
 
-/** Fulfill a promise by executing a given code */
-template<class R, class F>
-void fulfillPromise(std::promise<R>& promise, F code)
+/** A value or an exception (or nothing)
+ *
+ *  This is similar to `optional<expected<T>>`` but it with a Future/Promise
+ *  like API.
+ *
+ *  Also the name is not so great.
+ **/
+template<class T>
+class Result {
+public:
+  bool is_valid() const
+  {
+    return value_.which() > 0;
+  }
+  void set_exception(std::exception_ptr e)
+  {
+    value_ = std::move(e);
+  }
+  void set_value(T&& value)
+  {
+    value_ = std::move(value);
+  }
+  void set_value(T const& value)
+  {
+    value_ = value;
+  }
+
+  /** Extract the value from the future
+   *
+   *  After this, the value is invalid.
+   **/
+  T get()
+  {
+    switch (value_.which()) {
+      case 1: {
+        T value = std::move(boost::get<T>(value_));
+        value_  = boost::blank();
+        return value;
+      }
+      case 2: {
+        std::exception_ptr exception = std::move(boost::get<std::exception_ptr>(value_));
+        value_                       = boost::blank();
+        std::rethrow_exception(std::move(exception));
+        break;
+      }
+      default:
+        throw std::future_error(std::future_errc::no_state);
+    }
+  }
+private:
+  boost::variant<boost::blank, T, std::exception_ptr> value_;
+};
+
+template<>
+class Result<void> : public Result<std::nullptr_t>
 {
-  try {
-    promise.set_value(code());
+public:
+  void set_value()
+  {
+    Result<std::nullptr_t>::set_value(nullptr);
   }
-  catch(...) {
-    promise.set_exception(std::current_exception());
+  void get()
+  {
+    Result<std::nullptr_t>::get();
   }
-}
+};
 
-/** Fulfill a promise by executing a given code
+template<class T>
+class Result<T&> : public Result<std::reference_wrapper<T>>
+{
+public:
+  void set_value(T& value)
+  {
+    Result<std::reference_wrapper<T>>::set_value(std::ref(value));
+  }
+  T& get()
+  {
+    return Result<std::reference_wrapper<T>>::get();
+  }
+};
+
+/** Execute some code and set a promise or result accordingly
+ *
+ *  Roughly this does:
  *
- *  This is a special version for `std::promise<void>` because the default
- *  version does not compile in this case.
+ *  <pre>
+ *  promise.set_value(code());
+ *  </pre>
+ *
+ *  but it takes care of exceptions and works with `void`.
+ *
+ *  We might need this when working with generic code because
+ *  the trivial implementation does not work with `void` (before C++1z).
+ *
+ *  @param    code  What we want to do
+ *  @param  promise Where to want to store the result
  */
-template<class F>
-void fulfillPromise(std::promise<void>& promise, F code)
+template <class R, class F> auto fulfill_promise(R& promise, F&& code) -> decltype(promise.set_value(code()))
 {
   try {
-    (code)();
-    promise.set_value();
+    promise.set_value(std::forward<F>(code)());
+  } catch (...) {
+    promise.set_exception(std::current_exception());
   }
-  catch(...) {
+}
+
+template <class R, class F> auto fulfill_promise(R& promise, F&& code) -> decltype(promise.set_value())
+{
+  try {
+    std::forward<F>(code)();
+    promise.set_value();
+  } catch (...) {
     promise.set_exception(std::current_exception());
   }
 }
 
+/** Set a promise/result from a future/result
+ *
+ *  Roughly this does:
+ *
+ *  <pre>promise.set_value(future);</pre>
+ *
+ *  but it takes care of exceptions and works with `void`.
+ *
+ *  We might need this when working with generic code because
+ *  the trivial implementation does not work with `void` (before C++1z).
+ *
+ *  @param promise output (a valid future or a result)
+ *  @param future  input (a ready/waitable future or a valid result)
+ */
+template <class P, class F> inline void set_promise(P& promise, F&& future)
+{
+  fulfill_promise(promise, [&future] { return std::forward<F>(future).get(); });
+}
+
 }
 }