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