C++ 函数异步编程的性能调优指南

#include <iostream>
#include <fstream>
#include <future>

// 并行文件读取函数
std::string read_file_parallel(const std::string& filename) {
  // 获取并发线程数
  const auto num_threads = std::thread::hardware_concurrency();

  // 将文件分块并创建任务
  const auto file_size = std::ifstream(filename).seekg(0, std::ios::end).tellg();
  const auto block_size = file_size / num_threads;
  std::vector<std::future<std::string>> futures;

  for (auto i = 0; i < num_threads; ++i) {
    futures.emplace_back(std::async(std::launch::async,
      [filename, block_size, i] {
        std::ifstream file(filename);
        file.seekg(i * block_size, std::ios::beg);
        std::string block(block_size, '\0');
        file.read(&block[0], block_size);
        return block;
      }));
  }

  // 收集结果并返回
  std::string result;
  for (auto& future : futures) {
    result += future.get();
  }

  return result;
}

int main() {
  const auto result = read_file_parallel("file.txt");
  std::cout << "File contents: " << result << std::endl;
  return 0;
}