C++ - Multithreading in C++ (std::thread)

Multithreading is a feature in C++ that allows a program to run multiple tasks at the same time. Each task runs in a separate thread. A thread is a small unit of execution within a program. Using multiple threads helps programs perform tasks faster and make better use of the computer’s CPU.

In earlier programming models, programs usually executed instructions one after another in a single thread. This means the program had to finish one task before starting the next. With multithreading, a program can perform several tasks simultaneously, such as downloading a file while updating the user interface.

C++ introduced built-in multithreading support in the C++11 standard through the <thread> library. The std::thread class allows programmers to create and manage threads easily.

Basic working of threads in C++:

  1. A thread is created using the std::thread class.

  2. A function is assigned to the thread.

  3. The thread starts executing that function independently.

  4. The main program can wait for the thread to finish using the join() function.

Example:

#include <iostream>
#include <thread>
using namespace std;

void display() {
    cout << "Thread is running" << endl;
}

int main() {
    thread t1(display);  
    t1.join();           
    return 0;
}

In this example, a function named display() is executed in a separate thread. The join() function makes the main program wait until the thread finishes execution.

Important concepts in multithreading:

Thread Creation
A thread is created by passing a function to the std::thread constructor.

Thread Joining
The join() function ensures that the main thread waits for the created thread to complete before continuing.

Thread Detaching
The detach() function allows the thread to run independently from the main program.

Concurrency Issues
When multiple threads access the same data at the same time, problems like data inconsistency can occur. To avoid this, synchronization mechanisms such as mutexes and locks are used.

Advantages of multithreading:

  • Improves program performance.

  • Allows parallel execution of tasks.

  • Makes applications more responsive.

Disadvantages:

  • Programs become more complex to design.

  • Synchronization errors can occur if threads share data incorrectly.

Multithreading is widely used in applications like web servers, games, operating systems, and real-time data processing systems where multiple operations must run simultaneously.