C++(27): 线程池

目录

1. 概述

2. 例程

（1）ThreadPool.h

（2）ThreadPool.cpp

（3）Start.cpp

（4）编译

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1. 概述

线程池技术绝不是C++独有的，Java和Python都有比较晚完善的线程池构造接口。

通俗的讲，线程池只是一种管理线程的方式。很多时候，我们为了充分利用CPU和Memory资源，会创建一些独立的线程，执行同步或异步的任务。但有一个不得不考虑的问题是，现成的创建和销毁本身也是消耗系统资源的，尤其是一些需要频繁创建和销毁线程的应用场景下。当然有时候有一些连续的任务也不需要通过线程池技术来完成。

如上所述，为了避免频繁创建和销毁线程带来的系统资源的消耗，我们可以提前创建一定数量的线程，用来等待和处理队列中的事务，无需反复地创建和销毁线程。

2. 例程

（1）ThreadPool.h

#ifndef __THREADPOOL_H__#define __THREADPOOL_H__#include <iostream>  #include <vector>  #include <queue>  #include <thread>  #include <mutex>  #include <condition_variable>  #include <future>#include <functional>#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <stdint.h>class ThreadPool{public:  ThreadPool(size_t threads);template<class F, class... Args>  auto enqueue(F&& f, Args&&... args) -> std::future<typename std::result_of<F(Args...)>::type>{using return_type = typename std::result_of<F(Args...)>::type;  auto task = std::make_shared<std::packaged_task<return_type()>>(  std::bind(std::forward<F>(f), std::forward<Args>(args)...)  );  std::future<return_type> res = task->get_future();  {  std::unique_lock<std::mutex> lock(queueMutex);  if (stop) {  throw std::runtime_error("enqueue on stopped ThreadPool");  }  tasks.emplace([task]() { (*task)(); });  }  condition.notify_one();  return res;  }~ThreadPool();private:  std::vector<std::thread> workers;  std::queue<std::function<void()>> tasks;  std::mutex queueMutex;  std::condition_variable condition;  bool stop;  };#endif ///< __THREADPOOL_H__

（2）ThreadPool.cpp

#include "ThreadPool.h"ThreadPool::ThreadPool(size_t threads) : stop(false){for (size_t i = 0; i < threads; ++i) {  workers.emplace_back([this] {  while (true) {  std::function<void()> task;  {  std::unique_lock<std::mutex> lock(this->queueMutex);  this->condition.wait(lock, [this] { return this->stop || !this->tasks.empty(); });  if (this->stop && this->tasks.empty()) {  return;  }  task = std::move(this->tasks.front());  this->tasks.pop();  }  task();  }  });  }  }ThreadPool::~ThreadPool(){  {  std::unique_lock<std::mutex> lock(queueMutex);  stop = true;  }  condition.notify_all();  for (std::thread &worker : workers) {  worker.join();  }  }  

（3）Start.cpp

#include <iostream>  #include <vector>  #include <queue>  #include <thread>  #include <mutex>  #include <condition_variable>  #include <future>#include <functional>#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <stdint.h>#include "ThreadPool.h"/** sudo g++ -std=c++17 -o ./Start.bin ./*.cpp -lpthread */#define EXTERNAL_FUNC 0 ///< 0: 类内部成员///< 1: 类外部成员#if EXTERNAL_FUNC == 1// 定义一个返回整数的函数  int intFunction(int x){return x * x;}  // 定义一个返回字符串的函数  std::string stringFunction(std::string s){return s + " world";}int main(int argc, char* argv[]){ThreadPool pool(4);  // 使用enqueue来执行intFunction，传入参数4  auto result1 = pool.enqueue(intFunction, 4);  // 使用enqueue来执行stringFunction，传入参数"hello"  auto result2 = pool.enqueue(stringFunction, "hello");  // 获取并打印结果  std::cout << "result1: " << result1.get() << std::endl;  // 应该打印出16  std::cout << "result2: " << result2.get() << std::endl;  // 应该打印出"hello world"  return 0;  }#else ///< 作为类成员class DemoClass{public:  DemoClass(int num_threads = 1){if(num_threads <= 0 ){num_threads = 1;}pool = new ThreadPool(num_threads);}~DemoClass(){delete pool;pool = nullptr;}void printTask(int n){  std::cout << "Processing " << n << std::endl;}  void startProcessing(){for (int i = 1; i <= 50; ++i){pool->enqueue(&DemoClass::printTask, this, i);usleep(1); ///< 短暂的等待是有必要的.}  }private:ThreadPool* pool = nullptr;};  int main(int argc, char* argv[]){DemoClass myClass(10);  myClass.startProcessing();  return 0;  }#endif

（4）编译

sudo g++ -std=c++17 -o ./Start.bin ./*.cpp -lpthread