1 // Copyright 2021 gRPC authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef GRPC_SRC_CORE_LIB_PROMISE_JOIN_H 16 #define GRPC_SRC_CORE_LIB_PROMISE_JOIN_H 17 18 #include <grpc/support/port_platform.h> 19 20 #include <stdlib.h> 21 22 #include <tuple> 23 24 #include "absl/meta/type_traits.h" 25 26 #include "src/core/lib/promise/detail/join_state.h" 27 #include "src/core/lib/promise/map.h" 28 29 namespace grpc_core { 30 namespace promise_detail { 31 32 struct JoinTraits { 33 template <typename T> 34 using ResultType = absl::remove_reference_t<T>; 35 template <typename T> IsOkJoinTraits36 static bool IsOk(const T&) { 37 return true; 38 } 39 template <typename T> UnwrappedJoinTraits40 static T Unwrapped(T x) { 41 return x; 42 } 43 template <typename R, typename T> EarlyReturnJoinTraits44 static R EarlyReturn(T) { 45 abort(); 46 } 47 template <typename... A> FinalReturnJoinTraits48 static std::tuple<A...> FinalReturn(A... a) { 49 return std::make_tuple(std::move(a)...); 50 } 51 }; 52 53 template <typename... Promises> 54 class Join { 55 public: Join(Promises...promises)56 explicit Join(Promises... promises) : state_(std::move(promises)...) {} operator()57 auto operator()() { return state_.PollOnce(); } 58 59 private: 60 JoinState<JoinTraits, Promises...> state_; 61 }; 62 63 struct WrapInTuple { 64 template <typename T> operatorWrapInTuple65 std::tuple<T> operator()(T x) { 66 return std::make_tuple(std::move(x)); 67 } 68 }; 69 70 } // namespace promise_detail 71 72 /// Combinator to run all promises to completion, and return a tuple 73 /// of their results. 74 template <typename... Promise> Join(Promise...promises)75promise_detail::Join<Promise...> Join(Promise... promises) { 76 return promise_detail::Join<Promise...>(std::move(promises)...); 77 } 78 79 template <typename F> Join(F promise)80auto Join(F promise) { 81 return Map(std::move(promise), promise_detail::WrapInTuple{}); 82 } 83 84 } // namespace grpc_core 85 86 #endif // GRPC_SRC_CORE_LIB_PROMISE_JOIN_H 87