X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/a15797ea55151ddfdbae48147e74159efe01b411..d22f65624615098a556403243579dd7c4ceb69dd:/include/xbt/future.hpp

diff --git a/include/xbt/future.hpp b/include/xbt/future.hpp
index d5a31a55ce..a374bec117 100644
--- a/include/xbt/future.hpp
+++ b/include/xbt/future.hpp
@@ -7,35 +7,210 @@
 #ifndef XBT_FUTURE_HPP
 #define XBT_FUTURE_HPP
 
-#include <future>
-#include <utility>
+#include <cstddef>
+
 #include <exception>
+#include <functional>
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
 
 namespace simgrid {
 namespace xbt {
 
-/** Fulfill a promise by executing a given 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 {
+  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;
+  }
+  void set_exception(std::exception_ptr e)
+  {
+    this->reset();
+    new (&exception_) std::exception_ptr(std::move(e));
+    status_ = ResultStatus::exception;
+  }
+  void set_value(T&& value)
+  {
+    this->reset();
+    new (&value_) T(std::move(value));
+    status_ = ResultStatus::value;
+  }
+  void set_value(T const& value)
+  {
+    this->reset();
+    new (&value_) T(value);
+    status_ = ResultStatus::value;
+  }
+
+  /** Extract the value from the future
+   *
+   *  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);
+      }
+      case ResultStatus::exception: {
+        std::exception_ptr exception = std::move(exception_);
+        exception_.~exception_ptr();
+        status_ = ResultStatus::invalid;
+        std::rethrow_exception(std::move(exception));
+        break;
+      }
+    }
+  }
+private:
+  ResultStatus status_ = ResultStatus::invalid;
+  union {
+    T value_;
+    std::exception_ptr exception_;
+  };
+};
+
+template<>
+class Result<void> : public Result<std::nullptr_t>
+{
+public:
+  void set_value()
+  {
+    Result<std::nullptr_t>::set_value(nullptr);
+  }
+  void get()
+  {
+    Result<std::nullptr_t>::get();
+  }
+};
+
+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:
+ *
+ *  <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>
-void fulfillPromise(std::promise<R>& promise, F code)
+auto fulfillPromise(R& promise, F&& code)
+-> decltype(promise.set_value(code()))
 {
   try {
-    promise.set_value(code());
+    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 F>
-void fulfillPromise(std::promise<void>& promise, F code)
+template<class P, class F>
+auto fulfillPromise(P& promise, F&& code)
+-> decltype(promise.set_value())
 {
   try {
-    (code)();
+    std::forward<F>(code)();
     promise.set_value();
   }
   catch(...) {
@@ -43,6 +218,26 @@ void fulfillPromise(std::promise<void>& promise, F code)
   }
 }
 
+/** 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 setPromise(P& promise, F&& future)
+{
+  fulfillPromise(promise, [&]{ return std::forward<F>(future).get(); });
+}
+
 }
 }