| // Licensed to the Apache Software Foundation (ASF) under one |
| // or more contributor license agreements. See the NOTICE file |
| // distributed with this work for additional information |
| // regarding copyright ownership. The ASF licenses this file |
| // to you under the Apache License, Version 2.0 (the |
| // "License"); you may not use this file except in compliance |
| // with the License. You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, |
| // software distributed under the License is distributed on an |
| // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| // KIND, either express or implied. See the License for the |
| // specific language governing permissions and limitations |
| // under the License. |
| // |
| // Utility functions which are handy when doing async/callback-based programming. |
| #pragma once |
| |
| #include <functional> |
| #include <memory> |
| |
| #include "kudu/gutil/macros.h" |
| #include "kudu/util/countdown_latch.h" |
| #include "kudu/util/status.h" |
| #include "kudu/util/status_callback.h" |
| |
| namespace kudu { |
| |
| // Simple class which can be used to make async methods synchronous. |
| // For example: |
| // Synchronizer s; |
| // SomeAsyncMethod(s.AsStatusCallback()); |
| // CHECK_OK(s.Wait()); |
| // |
| // The lifetime of the synchronizer is decoupled from the callback it produces. |
| // If the callback outlives the synchronizer then executing it will be a no-op. |
| // Callers must be careful not to allow the callback to be destructed without |
| // completing it, otherwise the thread waiting on the synchronizer will block |
| // indefinitely. |
| class Synchronizer { |
| public: |
| Synchronizer() |
| : data_(std::make_shared<Data>()) { |
| } |
| |
| void StatusCB(const Status& status) { |
| Data::Callback(std::weak_ptr<Data>(data_), status); |
| } |
| |
| StatusCallback AsStatusCallback() { |
| std::weak_ptr<Data> w_data(data_); |
| return [w_data](const Status& s) { Data::Callback(w_data, s); }; |
| } |
| |
| Status Wait() const { |
| data_->latch.Wait(); |
| return data_->status; |
| } |
| |
| Status WaitFor(const MonoDelta& delta) const { |
| if (PREDICT_FALSE(!data_->latch.WaitFor(delta))) { |
| return Status::TimedOut("timed out while waiting for the callback to be called"); |
| } |
| return data_->status; |
| } |
| |
| Status WaitUntil(const MonoTime& deadline) const { |
| if (PREDICT_FALSE(!data_->latch.WaitUntil(deadline))) { |
| return Status::TimedOut("timed out while waiting for the callback to be called"); |
| } |
| return data_->status; |
| } |
| |
| void Reset() { |
| data_->latch.Reset(1); |
| } |
| |
| private: |
| |
| struct Data { |
| Data() : latch(1) { |
| } |
| |
| static void Callback(std::weak_ptr<Data> weak, const Status& status) { |
| auto ptr = weak.lock(); |
| if (ptr) { |
| ptr->status = status; |
| ptr->latch.CountDown(); |
| } |
| } |
| |
| Status status; |
| CountDownLatch latch; |
| DISALLOW_COPY_AND_ASSIGN(Data); |
| }; |
| |
| std::shared_ptr<Data> data_; |
| }; |
| } // namespace kudu |