How to use multithreading efficiently in C++?

Using multithreading in C++ can improve parallelism: Create threads: Use the std::thread class or the pthread library to create threads. Synchronize threads: Use synchronization mechanisms such as mutexes and condition variables to ensure thread safety. Practical case: For example, if multiple files are processed in parallel, multiple threads are created to process each file to improve efficiency.

Using Multithreading Efficiently in C++

Multi-threaded programming is crucial in software development as it improves Parallelism and application performance. This article will introduce how to effectively use multi-threading features in C++, including thread creation, synchronization and practical cases.

Thread creation

There are two ways to create a thread in C++:

1. std::thread class:# Introduced in ##C++11, providing a modern way to create and manage threads. Use the std::thread constructor, passing the thread function and any parameters.

std::thread t(my_function, arg1, arg2);

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2. pthread library: Another option is to use the POSIX threads (pthread) library. Include the pthread.h header file and use the pthread_create function to create the thread.

pthread_t t;
pthread_create(&t, NULL, my_function, arg1);

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Thread synchronization

1. Mutex: The std::mutex class controls exclusive access to shared data. Only one thread is allowed to hold the mutex lock at the same time.

std::mutex m;
{
    std::lock_guard<std::mutex> lock(m);
    // 对共享数据进行操作
}

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2. Condition variable: std::condition_variable class is used to notify threads about changes in conditions. The thread can wait for the condition to be met before continuing execution.

std::condition_variable cv;
std::mutex m;
{
    std::unique_lock<std::mutex> lock(m);
    // 等待条件达成
    cv.wait(lock);
}

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Practical Case: Concurrent File Processing

#include <iostream>
#include <fstream>
#include <vector>
#include <thread>

using namespace std;

void process_file(string filename, ofstream& out)
{
    ifstream in(filename);
    string line;
    while (getline(in, line))
    {
        out << line << endl;
    }
}

int main()
{
    // 文件名列表
    vector<string> filenames = {"file1.txt", "file2.txt", "file3.txt"};

    // 创建 output 输出文件
    ofstream out("output.txt");

    // 创建线程向量
    vector<thread> threads;

    // 为每个文件创建线程
    for (auto& filename : filenames)
    {
        threads.emplace_back(process_file, filename, ref(out));
    }

    // 等待线程完成
    for (auto& thread : threads)
    {
        thread.join();
    }

    cout << "Files processed successfully." << endl;
    return 0;
}

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