X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/74950d38bb412bfa1489d8ce0a8c5a194fe87a45..2e60fe3cfd5cf5305888fcca0ae19700d808bb23:/include/xbt/future.hpp

diff --git a/include/xbt/future.hpp b/include/xbt/future.hpp
index 122d59093b..ac75bf6747 100644
--- a/include/xbt/future.hpp
+++ b/include/xbt/future.hpp
@@ -1,4 +1,4 @@
-/* Copyright (c) 2015-2016. The SimGrid Team.
+/* Copyright (c) 2015-2020. The SimGrid Team.
  * All rights reserved.                                                     */
 
 /* This program is free software; you can redistribute it and/or modify it
@@ -9,142 +9,74 @@
 
 #include <cstddef>
 
-#include <utility>
+#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 {
 
-/** A value or an exception
+/** A value or an exception (or nothing)
  *
- *  The API is similar to the one of future and promise.
+ *  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 {
-  enum class ResultStatus {
-    invalid,
-    value,
-    exception,
-  };
 public:
-  Result() {}
-  ~Result() { this->reset(); }
-
-  // Copy (if T is copyable) and move:
-  Result(Result const& that)
-  {
-    (*this) = that;
-  }
-  Result& operator=(Result const& that)
-  {
-    this->reset();
-    switch (that.status_) {
-      case ResultStatus::invalid:
-        break;
-      case ResultStatus::valid:
-        new (&value_) T(that.value);
-        break;
-      case ResultStatus::exception:
-        new (&exception_) T(that.exception);
-        break;
-    }
-    return *this;
-  }
-  Result(Result&& that)
-  {
-    *this = std::move(that);
-  }
-  Result& operator=(Result&& that)
-  {
-    this->reset();
-    switch (that.status_) {
-      case ResultStatus::invalid:
-        break;
-      case ResultStatus::valid:
-        new (&value_) T(std::move(that.value));
-        that.value.~T();
-        break;
-      case ResultStatus::exception:
-        new (&exception_) T(std::move(that.exception));
-        that.exception.~exception_ptr();
-        break;
-    }
-    that.status_ = ResultStatus::invalid;
-    return *this;
-  }
-
   bool is_valid() const
   {
-    return status_ != ResultStatus::invalid;
-  }
-  void reset()
-  {
-    switch (status_) {
-      case ResultStatus::invalid:
-        break;
-      case ResultStatus::value:
-        value_.~T();
-        break;
-      case ResultStatus::exception:
-        exception_.~exception_ptr();
-        break;
-    }
-    status_ = ResultStatus::invalid;
+    return value_.which() > 0;
   }
   void set_exception(std::exception_ptr e)
   {
-    this->reset();
-    new (&exception_) std::exception_ptr(std::move(e));
-    status_ = ResultStatus::exception;
+    value_ = std::move(e);
   }
   void set_value(T&& value)
   {
-    this->reset();
-    new (&value_) T(std::move(value));
-    status_ = ResultStatus::value;
+    value_ = std::move(value);
   }
   void set_value(T const& value)
   {
-    this->reset();
-    new (&value_) T(value);
-    status_ = ResultStatus::value;
+    value_ = value;
   }
 
   /** Extract the value from the future
    *
-   *  After this the value is invalid.
+   *  After this, the value is invalid.
    **/
   T get()
   {
-    switch (status_) {
-      case ResultStatus::invalid:
-      default:
-        throw std::logic_error("Invalid result");
-      case ResultStatus::value: {
-        T value = std::move(value_);
-        value_.~T();
-        status_ = ResultStatus::invalid;
-        return std::move(value);
+    switch (value_.which()) {
+      case 1: {
+        T value = std::move(boost::get<T>(value_));
+        value_  = boost::blank();
+        return value;
       }
-      case ResultStatus::exception: {
-        std::exception_ptr exception = std::move(exception_);
-        exception_.~exception_ptr();
-        status_ = ResultStatus::invalid;
+      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:
-  ResultStatus status_ = ResultStatus::invalid;
-  union {
-    T value_;
-    std::exception_ptr exception_;
-  };
+  boost::variant<boost::blank, T, std::exception_ptr> value_;
 };
 
 template<>
-class Result<void> : public Result<nullptr_t>
+class Result<void> : public Result<std::nullptr_t>
 {
 public:
   void set_value()
@@ -153,7 +85,7 @@ public:
   }
   void get()
   {
-    Result<nullptr_t>::get();
+    Result<std::nullptr_t>::get();
   }
 };
 
@@ -171,37 +103,60 @@ public:
   }
 };
 
-/** Fulfill a promise by executing a given code */
-template<class R, class F>
-auto fulfillPromise(R& promise, F&& code)
--> decltype(promise.set_value(code()))
+/** Execute some code and set a promise or result accordingly
+ *
+ *  Roughly this does:
+ *
+ *  <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 R, class F> auto fulfill_promise(R& promise, F&& code) -> decltype(promise.set_value(code()))
 {
   try {
-    promise.set_value(code());
-  }
-  catch(...) {
+    promise.set_value(std::forward<F>(code)());
+  } catch (...) {
     promise.set_exception(std::current_exception());
   }
 }
 
-/** Fulfill a promise by executing a given code
- *
- *  This is a special version for `std::promise<void>` because the default
- *  version does not compile in this case.
- */
-template<class P, class F>
-auto fulfillPromise(P& promise, F&& code)
--> decltype(promise.set_value())
+template <class R, class F> auto fulfill_promise(R& promise, F&& code) -> decltype(promise.set_value())
 {
   try {
-    (code)();
+    std::forward<F>(code)();
     promise.set_value();
-  }
-  catch(...) {
+  } 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(); });
+}
+
 }
 }