-/* 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
#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<>
* promise.set_value(code());
* </pre>
*
- * but it takes care of exceptions and works with void.
+ * 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 fulfillPromise(R& promise, F&& code)
--> decltype(promise.set_value(code()))
+template <class R, class F> auto fulfill_promise(R& promise, F&& code) -> decltype(promise.set_value(code()))
{
try {
promise.set_value(std::forward<F>(code)());
- }
- catch(...) {
+ } catch (...) {
promise.set_exception(std::current_exception());
}
}
-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 {
std::forward<F>(code)();
promise.set_value();
- }
- catch(...) {
+ } catch (...) {
promise.set_exception(std::current_exception());
}
}
-/** Set a promise/result from a future/resul
+/** Set a promise/result from a future/result
*
* Roughly this does:
*
* @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)
+template <class P, class F> inline void set_promise(P& promise, F&& future)
{
- fulfillPromise(promise, [&]{ return std::forward<F>(future).get(); });
+ fulfill_promise(promise, [&future] { return std::forward<F>(future).get(); });
}
}
