| /* |
| * Copyright (C) 2021 The Android Open Source Project |
| * |
| * Licensed 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. |
| */ |
| |
| #pragma once |
| |
| #include <sched.h> |
| |
| #include <condition_variable> |
| #include <mutex> |
| #include <thread> |
| |
| template <typename Impl> |
| class StreamWorker { |
| enum class WorkerState { STOPPED, RUNNING, PAUSE_REQUESTED, PAUSED, RESUME_REQUESTED, ERROR }; |
| |
| public: |
| StreamWorker() = default; |
| ~StreamWorker() { stop(); } |
| bool start() { |
| mWorker = std::thread(&StreamWorker::workerThread, this); |
| std::unique_lock<std::mutex> lock(mWorkerLock); |
| mWorkerCv.wait(lock, [&] { return mWorkerState != WorkerState::STOPPED; }); |
| return mWorkerState == WorkerState::RUNNING; |
| } |
| void pause() { switchWorkerStateSync(WorkerState::RUNNING, WorkerState::PAUSE_REQUESTED); } |
| void resume() { switchWorkerStateSync(WorkerState::PAUSED, WorkerState::RESUME_REQUESTED); } |
| bool hasError() { |
| std::lock_guard<std::mutex> lock(mWorkerLock); |
| return mWorkerState == WorkerState::ERROR; |
| } |
| void stop() { |
| { |
| std::lock_guard<std::mutex> lock(mWorkerLock); |
| if (mWorkerState == WorkerState::STOPPED) return; |
| mWorkerState = WorkerState::STOPPED; |
| } |
| if (mWorker.joinable()) { |
| mWorker.join(); |
| } |
| } |
| bool waitForAtLeastOneCycle() { |
| WorkerState newState; |
| switchWorkerStateSync(WorkerState::RUNNING, WorkerState::PAUSE_REQUESTED, &newState); |
| if (newState != WorkerState::PAUSED) return false; |
| switchWorkerStateSync(newState, WorkerState::RESUME_REQUESTED, &newState); |
| return newState == WorkerState::RUNNING; |
| } |
| |
| // Methods that need to be provided by subclasses: |
| // |
| // Called once at the beginning of the thread loop. Must return |
| // 'true' to enter the thread loop, otherwise the thread loop |
| // exits and the worker switches into the 'error' state. |
| // bool workerInit(); |
| // |
| // Called for each thread loop unless the thread is in 'paused' state. |
| // Must return 'true' to continue running, otherwise the thread loop |
| // exits and the worker switches into the 'error' state. |
| // bool workerCycle(); |
| |
| private: |
| void switchWorkerStateSync(WorkerState oldState, WorkerState newState, |
| WorkerState* finalState = nullptr) { |
| std::unique_lock<std::mutex> lock(mWorkerLock); |
| if (mWorkerState != oldState) { |
| if (finalState) *finalState = mWorkerState; |
| return; |
| } |
| mWorkerState = newState; |
| mWorkerCv.wait(lock, [&] { return mWorkerState != newState; }); |
| if (finalState) *finalState = mWorkerState; |
| } |
| void workerThread() { |
| bool success = static_cast<Impl*>(this)->workerInit(); |
| { |
| std::lock_guard<std::mutex> lock(mWorkerLock); |
| mWorkerState = success ? WorkerState::RUNNING : WorkerState::ERROR; |
| } |
| mWorkerCv.notify_one(); |
| if (!success) return; |
| |
| for (WorkerState state = WorkerState::RUNNING; state != WorkerState::STOPPED;) { |
| bool needToNotify = false; |
| if (state != WorkerState::PAUSED ? static_cast<Impl*>(this)->workerCycle() |
| : (sched_yield(), true)) { |
| // |
| // Pause and resume are synchronous. One worker cycle must complete |
| // before the worker indicates a state change. This is how 'mWorkerState' and |
| // 'state' interact: |
| // |
| // mWorkerState == RUNNING |
| // client sets mWorkerState := PAUSE_REQUESTED |
| // last workerCycle gets executed, state := mWorkerState := PAUSED by us |
| // (or the workers enters the 'error' state if workerCycle fails) |
| // client gets notified about state change in any case |
| // thread is doing a busy wait while 'state == PAUSED' |
| // client sets mWorkerState := RESUME_REQUESTED |
| // state := mWorkerState (RESUME_REQUESTED) |
| // mWorkerState := RUNNING, but we don't notify the client yet |
| // first workerCycle gets executed, the code below triggers a client notification |
| // (or if workerCycle fails, worker enters 'error' state and also notifies) |
| // state := mWorkerState (RUNNING) |
| if (state == WorkerState::RESUME_REQUESTED) { |
| needToNotify = true; |
| } |
| std::lock_guard<std::mutex> lock(mWorkerLock); |
| state = mWorkerState; |
| if (mWorkerState == WorkerState::PAUSE_REQUESTED) { |
| state = mWorkerState = WorkerState::PAUSED; |
| needToNotify = true; |
| } else if (mWorkerState == WorkerState::RESUME_REQUESTED) { |
| mWorkerState = WorkerState::RUNNING; |
| } |
| } else { |
| std::lock_guard<std::mutex> lock(mWorkerLock); |
| if (state == WorkerState::RESUME_REQUESTED || |
| mWorkerState == WorkerState::PAUSE_REQUESTED) { |
| needToNotify = true; |
| } |
| mWorkerState = WorkerState::ERROR; |
| state = WorkerState::STOPPED; |
| } |
| if (needToNotify) { |
| mWorkerCv.notify_one(); |
| } |
| } |
| } |
| |
| std::thread mWorker; |
| std::mutex mWorkerLock; |
| std::condition_variable mWorkerCv; |
| WorkerState mWorkerState = WorkerState::STOPPED; // GUARDED_BY(mWorkerLock); |
| }; |