Multithreading and Concurrency

Understanding Multithreading in C++

Multithreading allows a program to perform multiple tasks concurrently within the same process space. It involves creating multiple threads, with each thread executing part of the program code. In C++, threads are represented by the std::thread class, part of the <thread> header introduced in C++11.

Creating and Managing Threads

Creating a Thread: To create a thread, instantiate an std::thread object and pass the function to be executed by the thread as an argument.

void task1() {
     // Task code here 
}

std::thread t1(task1); // Creates a thread executing task1

Joining Threads: To ensure a thread has completed execution before continuing, use the join() method. Joining a thread blocks the calling thread until the thread represented by the std::thread object completes.

t1.join(); // Main thread waits for t1 to finish

Detaching Threads: Threads can also be detached, allowing them to run independently from the main thread. A detached thread releases its resources automatically upon completion.

t1.detach(); // t1 will run independently

Concurrency vs. Parallelism

While often used interchangeably, concurrency and parallelism have distinct meanings in the context of programming. Concurrency refers to the ability of a program to deal with multiple tasks at once, which might not necessarily be executing simultaneously. Parallelism, on the other hand, involves performing multiple operations truly in parallel, leveraging multi-core processors.

Synchronization and Data Safety

Managing access to shared data is a critical aspect of multithreaded programming to prevent data races and ensure thread safety.

Mutexes: Mutexes (mutual exclusions) are used to protect shared data by ensuring that only one thread can access the data at a time.

std::mutex mtx;
mtx.lock(); // Lock the mutex
 // Critical section
mtx.unlock(); // Unlock the mutex

Lock Guards: C++ introduces std::lock_guard, a scope-based mutex locker, ensuring that a mutex is properly released when the control leaves the scope, thus preventing deadlocks.

{
     std::lock_guard<std::mutex> guard(mtx);

     // Critical section 
}
// Mutex is automatically released here