With the introduction of C++20, the <thread> header now provides a useful addition called std::jthread. std::jthread is a type of thread that automatically joins on destruction, making it easier to manage and clean up threads. It is an improvement over traditional std::thread where you need to explicitly call join() or detach() to handle thread termination.

In this article, we will explore some practical examples of using std::jthread to build multi-threaded applications.

1. Creating Background Tasks

One common use case for std::jthread is executing background tasks concurrently. Here’s an example of how you can utilize it:

#include <iostream>
#include <thread>
#include <chrono>

void backgroundTask()
{
    // Simulating some time-consuming operation
    std::this_thread::sleep_for(std::chrono::seconds(5));
    std::cout << "Background task completed!" << std::endl;
}

int main()
{
    std::jthread backgroundThread(backgroundTask);

    // Perform other tasks concurrently

    return 0;
}

In this example, we create a std::jthread object named backgroundThread and pass in the backgroundTask function. The background task executes concurrently while the main thread continues executing other tasks.

2. Graceful Shutdown Handling

Another useful feature of std::jthread is its ability to gracefully handle thread termination. Let’s consider an example where we have a server that accepts incoming client connections and spawns individual threads to handle them:

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

std::atomic_bool serverRunning(true);

void clientHandler(int clientId)
{
    while (serverRunning)
    {
        // Handle client request
        std::cout << "Handling request for client " << clientId << std::endl;
        // ...
    }
}

int main()
{
    std::cout << "Server started!" << std::endl;

    std::vector<std::jthread> clientThreads;

    for (int i = 1; i <= 10; ++i)
    {
        std::jthread clientThread(clientHandler, i);
        clientThreads.push_back(std::move(clientThread));
    }

    std::cin.get(); // Wait for user input to stop the server
    serverRunning = false;

    // Join all the client threads
    for (auto& thread : clientThreads)
    {
        thread.join();
    }

    std::cout << "Server stopped!" << std::endl;

    return 0;
}

In this example, we have a server that spawns std::jthread objects to handle incoming client connections. The clientHandler function runs in a loop until the serverRunning flag is set to false. When the flag is set, all the threads gracefully terminate by finishing their iterations and returning control to the main thread.

With std::jthread, it becomes much easier to handle the graceful shutdown of threads without having to worry about explicitly joining them or detaching them.

Conclusion

std::jthread is a helpful addition to C++20 for managing threads. It simplifies the management of thread termination by automatically handling the join operation on destruction. We have explored two practical examples of its usage: executing background tasks and gracefully shutting down threads. By utilizing std::jthread, you can write cleaner and safer multi-threaded applications in C++.

#cpp #stdjthread