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129 lines
3.7 KiB
C++
129 lines
3.7 KiB
C++
// Licensed to the Apache Software Foundation (ASF) under one
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// or more contributor license agreements. See the NOTICE file
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// distributed with this work for additional information
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// regarding copyright ownership. The ASF licenses this file
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// to you under the Apache License, Version 2.0 (the
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// "License"); you may not use this file except in compliance
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// with the License. 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,
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// software distributed under the License is distributed on an
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// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations
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// under the License.
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#pragma once
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#include <vector>
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#include <queue>
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#include <memory>
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#include <thread>
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#include <mutex>
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#include <condition_variable>
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#include <future>
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#include <functional>
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#include <stdexcept>
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#define MAX_THREADS_NUM 32
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namespace zilliz {
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namespace milvus {
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class ThreadPool {
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public:
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ThreadPool(size_t threads, size_t queue_size = 1000);
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template<class F, class... Args>
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auto enqueue(F &&f, Args &&... args)
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-> std::future<typename std::result_of<F(Args...)>::type>;
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~ThreadPool();
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private:
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// need to keep track of threads so we can join them
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std::vector<std::thread> workers;
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// the task queue
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std::queue<std::function<void()> > tasks;
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size_t max_queue_size;
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// synchronization
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std::mutex queue_mutex;
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std::condition_variable condition;
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bool stop;
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};
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// the constructor just launches some amount of workers
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inline ThreadPool::ThreadPool(size_t threads, size_t queue_size)
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: max_queue_size(queue_size), stop(false) {
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for (size_t i = 0; i < threads; ++i)
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workers.emplace_back(
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[this] {
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for (;;) {
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std::function<void()> task;
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{
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std::unique_lock<std::mutex> lock(this->queue_mutex);
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this->condition.wait(lock,
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[this] { return this->stop || !this->tasks.empty(); });
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if (this->stop && this->tasks.empty())
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return;
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task = std::move(this->tasks.front());
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this->tasks.pop();
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}
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this->condition.notify_all();
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task();
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}
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}
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);
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}
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// add new work item to the pool
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template<class F, class... Args>
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auto ThreadPool::enqueue(F &&f, Args &&... args)
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-> std::future<typename std::result_of<F(Args...)>::type> {
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using return_type = typename std::result_of<F(Args...)>::type;
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auto task = std::make_shared<std::packaged_task<return_type()> >(
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std::bind(std::forward<F>(f), std::forward<Args>(args)...)
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);
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std::future<return_type> res = task->get_future();
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{
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std::unique_lock<std::mutex> lock(queue_mutex);
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this->condition.wait(lock,
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[this] { return this->tasks.size() < max_queue_size; });
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// don't allow enqueueing after stopping the pool
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if (stop)
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throw std::runtime_error("enqueue on stopped ThreadPool");
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tasks.emplace([task]() { (*task)(); });
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}
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condition.notify_all();
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return res;
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}
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// the destructor joins all threads
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inline ThreadPool::~ThreadPool() {
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{
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std::unique_lock<std::mutex> lock(queue_mutex);
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stop = true;
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}
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condition.notify_all();
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for (std::thread &worker: workers)
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worker.join();
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}
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}
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}
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