1 // Copyright 2023 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_WAIT_FOR_CALLBACK_H 16 #define GRPC_SRC_CORE_LIB_PROMISE_WAIT_FOR_CALLBACK_H 17 18 #include <grpc/support/port_platform.h> 19 20 #include <memory> 21 #include <utility> 22 23 #include "absl/base/thread_annotations.h" 24 25 #include "src/core/lib/gprpp/sync.h" 26 #include "src/core/lib/promise/activity.h" 27 #include "src/core/lib/promise/poll.h" 28 29 namespace grpc_core { 30 31 // Bridge callback interfaces and promise interfaces. 32 // This class helps bridge older callback interfaces with promises: 33 // MakeWaitPromise() returns a promise that will wait until a callback created 34 // by MakeCallback() has been invoked. 35 class WaitForCallback { 36 public: 37 // Creates a promise that blocks until the callback is invoked. MakeWaitPromise()38 auto MakeWaitPromise() { 39 return [state = state_]() -> Poll<Empty> { 40 MutexLock lock(&state->mutex); 41 if (state->done) return Empty{}; 42 state->waker = GetContext<Activity>()->MakeNonOwningWaker(); 43 return Pending{}; 44 }; 45 } 46 47 // Creates a callback that unblocks the promise. MakeCallback()48 auto MakeCallback() { 49 return [state = state_]() { 50 ReleasableMutexLock lock(&state->mutex); 51 state->done = true; 52 auto waker = std::move(state->waker); 53 lock.Release(); 54 waker.Wakeup(); 55 }; 56 } 57 58 private: 59 struct State { 60 Mutex mutex; 61 bool done ABSL_GUARDED_BY(mutex) = false; 62 Waker waker ABSL_GUARDED_BY(mutex); 63 }; 64 const std::shared_ptr<State> state_{std::make_shared<State>()}; 65 }; 66 67 } // namespace grpc_core 68 69 #endif // GRPC_SRC_CORE_LIB_PROMISE_WAIT_FOR_CALLBACK_H 70