A preliminary study on concurrent programming in C++

With the continuous improvement of computer hardware performance, people's need for multi-core processing is becoming stronger and stronger. At the same time, modern operating systems also provide increasingly complete support for concurrent programming, which makes concurrent programming an indispensable part of the programming field. In this context, C, as a widely used high-performance programming language, also provides many powerful concurrent programming tools and libraries.

This article will introduce some basic C concurrent programming concepts and techniques and demonstrate their use through simple example code.

Multi-threading Basics

Multi-threading is a commonly used concurrent programming model that allows a program to execute multiple instruction streams at the same time. In C, multi-thread programming can be accomplished through the header file in the standard library. The following is a simple example code using multi-threading:

#include <iostream>
#include <thread>

void hello() {
    std::cout << "Hello" << std::endl;
}

int main() {
    std::thread t(hello);
    t.join();
    return 0;
}

This code defines a function named hello, which will output the string "Hello". In the main function, the program creates a new thread t and uses the hello function as the execution function of the thread. The t.join() statement waits for the thread to finish executing before exiting the program.

Mutex lock

Due to the simultaneous execution of multiple threads, the same shared resources may be accessed at the same time. At this time, a mechanism is needed to ensure that only one thread can access the shared resource at any time. This mechanism is a mutex lock.

In C, you can use the header file in the standard library to implement a mutex lock. The following is a simple example code using a mutex lock:

#include <iostream>
#include <thread>
#include <mutex>

std::mutex m;
int sum = 0;

void add() {
    m.lock();
    sum += 1;
    m.unlock();
}

int main() {
    std::thread t1(add);
    std::thread t2(add);
    t1.join();
    t2.join();
    std::cout << "sum = " << sum << std::endl;
    return 0;
}

This code defines a function named add, which will increase the global variable sum by 1. In the main function, the program creates two new threads t1 and t2, and uses the add function as their execution function. Since sum is a shared resource, a mutex lock m is used in the add function to ensure that access to sum is thread-safe.

Atomic operation

Atomic operation is a special operation that can update or read shared resources without locking. In C, atomic operations can be implemented using the header file in the standard library. The following is a simple example code using atomic operations:

#include <iostream>
#include <thread>
#include <atomic>

std::atomic<int> sum(0);

void add() {
    sum += 1;
}

int main() {
    std::thread t1(add);
    std::thread t2(add);
    t1.join();
    t2.join();
    std::cout << "sum = " << sum << std::endl;
    return 0;
}

This code defines an atomic variable named sum, whose initial value is 0. In the add function, the atomic operation sum = 1 is used to increase the value of sum by 1. In the main function, the program creates two new threads t1 and t2, and uses the add function as their execution function. Since sum is an atomic variable, the atomic operation sum = 1 can guarantee thread safety.

Summary

This article introduces the basics of concurrent programming in C, including multi-threading, mutex locks and atomic operations. Of course, C provides far more concurrent programming tools and libraries than these, such as condition variables, semaphores, thread pools, and so on. In actual projects, choosing appropriate concurrent programming tools and libraries is of great significance to ensure the correctness of the program and improve program performance and maintainability.

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