Better C++ coroutine lifetime in actors KIKIMR-18962

1 files changed, 113 insertions, 0 deletions

diff --git a/library/cpp/actors/cppcoro/task_result.h b/library/cpp/actors/cppcoro/task_result.h
new file mode 100644
index 0000000000..70176e64d5
--- /dev/null
+++ b/library/cpp/actors/cppcoro/task_result.h
@@ -0,0 +1,113 @@
+#pragma once
+#include <util/system/yassert.h>
+#include <exception>
+#include <variant>
+
+namespace NActors {
+
+    namespace NDetail {
+
+        struct TVoid {};
+
+        template<class T>
+        struct TReplaceVoid {
+            using TType = T;
+        };
+
+        template<>
+        struct TReplaceVoid<void> {
+            using TType = TVoid;
+        };
+
+        template<class T>
+        struct TLValue {
+            using TType = T&;
+        };
+
+        template<>
+        struct TLValue<void> {
+            using TType = void;
+        };
+
+        template<class T>
+        struct TRValue {
+            using TType = T&&;
+        };
+
+        template<>
+        struct TRValue<void> {
+            using TType = void;
+        };
+
+    } // namespace NDetail
+
+    /**
+     * Wrapper for the task result
+     */
+    template<class T>
+    class TTaskResult {
+    public:
+        void SetValue()
+            requires (std::same_as<T, void>)
+        {
+            Result.template emplace<1>();
+        }
+
+        template<class TResult>
+        void SetValue(TResult&& result)
+            requires (!std::same_as<T, void>)
+        {
+            Result.template emplace<1>(std::forward<TResult>(result));
+        }
+
+        void SetException(std::exception_ptr&& e) noexcept {
+            Result.template emplace<2>(std::move(e));
+        }
+
+        typename NDetail::TLValue<T>::TType Value() & {
+            switch (Result.index()) {
+                case 0: {
+                    Y_FAIL("Task result has no value");
+                }
+                case 1: {
+                    if constexpr (std::same_as<T, void>) {
+                        return;
+                    } else {
+                        return std::get<1>(Result);
+                    }
+                }
+                case 2: {
+                    std::exception_ptr& e = std::get<2>(Result);
+                    Y_VERIFY_DEBUG(e, "Task exception missing");
+                    std::rethrow_exception(e);
+                }
+            }
+            Y_FAIL("Task result has an invalid state");
+        }
+
+        typename NDetail::TRValue<T>::TType Value() && {
+            switch (Result.index()) {
+                case 0: {
+                    Y_FAIL("Task result has no value");
+                }
+                case 1: {
+                    if constexpr (std::same_as<T, void>) {
+                        return;
+                    } else {
+                        return std::get<1>(std::move(Result));
+                    }
+                }
+                case 2: {
+                    std::exception_ptr& e = std::get<2>(Result);
+                    Y_VERIFY_DEBUG(e, "Task exception missing");
+                    std::rethrow_exception(std::move(e));
+                }
+            }
+            Y_FAIL("Task result has an invalid state");
+        }
+
+    private:
+        std::variant<std::monostate, typename NDetail::TReplaceVoid<T>::TType, std::exception_ptr> Result;
+    };
+
+} // namespace NActors