80 lines
3.2 KiB
C++
80 lines
3.2 KiB
C++
/*
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* Copyright (C) 2021 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <mutex>
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#include <optional>
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#include <queue>
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#include <thread>
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#include "Callable.h"
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namespace aidl::android::hardware::biometrics::fingerprint {
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// A class that encapsulates a worker thread and a task queue, and provides a convenient interface
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// for a Session to schedule its tasks for asynchronous execution.
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class WorkerThread final {
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public:
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// Internally creates a queue that cannot exceed maxQueueSize elements and a new thread that
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// polls the queue for tasks until this instance is destructed.
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explicit WorkerThread(size_t maxQueueSize);
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// Unblocks the internal queue and calls join on the internal thread allowing it to gracefully
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// exit.
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~WorkerThread();
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// Disallow copying this class.
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WorkerThread(const WorkerThread&) = delete;
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WorkerThread& operator=(const WorkerThread&) = delete;
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// Also disable moving this class to simplify implementation.
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WorkerThread(WorkerThread&&) = delete;
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WorkerThread& operator=(WorkerThread&&) = delete;
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// If the internal queue is not full, pushes a task at the end of the queue and returns true.
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// Otherwise, returns false. If the queue is busy, blocks until it becomes available.
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// This method expects heap-allocated tasks because it's the simplest way to represent function
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// objects of any type. Stack-allocated std::function could be used instead, but it cannot
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// represent functions with move-only captures because std::function is inherently copyable.
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// Not being able to pass move-only lambdas is a major limitation for the HAL implementation,
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// so heap-allocated tasks that share a common interface (Callable) were chosen instead.
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bool schedule(std::unique_ptr<Callable> task);
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private:
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// The function that runs on the internal thread. Sequentially runs the available tasks from
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// the queue. If the queue is empty, waits until a new task is added. If the worker is being
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// destructed, finishes its current task and gracefully exits.
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void threadFunc();
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// The maximum size that the queue is allowed to expand to.
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size_t mMaxSize;
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// Whether the destructor was called. If true, tells threadFunc to exit as soon as possible, and
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// tells schedule to avoid doing any work.
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std::atomic<bool> mIsDestructing;
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// Queue that's guarded by mQueueMutex and mQueueCond.
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std::deque<std::unique_ptr<Callable>> mQueue;
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std::mutex mQueueMutex;
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std::condition_variable mQueueCond;
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// The internal thread that works on the tasks from the queue.
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std::thread mThread;
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};
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} // namespace aidl::android::hardware::biometrics::fingerprint
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