Concurrency is an essential aspect of modern software development, enabling programs to efficiently execute multiple tasks simultaneously. C++ provides various concurrency models and synchronization primitives to help developers write concurrent programs reliably and efficiently. In this blog post, we will explore some of these models and primitives.
Table of Contents
- Introduction to Concurrency
- Thread-based Concurrency
- Task-based Concurrency
- Synchronization Primitives
- Conclusion
Introduction to Concurrency
Concurrency refers to the ability of a program to execute multiple tasks simultaneously, or in overlapping time intervals. It is particularly useful when dealing with I/O operations, CPU-intensive tasks, or improving overall system responsiveness.
Thread-based Concurrency
Threads are a fundamental unit of concurrency in C++. They represent independent paths of execution within a program. C++ provides the std::thread class, which allows developers to create and manage threads easily. By creating multiple threads, we can execute different parts of a program concurrently.
#include <thread>
void SomeFunction()
{
// Code to be executed by the thread
}
int main()
{
std::thread myThread(SomeFunction);
// Do other operations concurrently
myThread.join();
return 0;
}
Task-based Concurrency
Task-based concurrency is an alternative model to thread-based concurrency. It focuses on dividing the program’s work into smaller tasks, which can be executed concurrently by a task scheduler. C++ provides the <future> header with the std::async and std::future classes, which facilitate task-based concurrency.
#include <future>
int SomeFunction()
{
// Code to be executed by the task
return 42;
}
int main()
{
std::future<int> result = std::async(std::launch::async, SomeFunction);
// Do other operations concurrently
int value = result.get();
return 0;
}
Synchronization Primitives
When multiple threads or tasks access shared resources, synchronization is necessary to ensure data consistency and avoid race conditions. C++ provides several synchronization primitives for this purpose.
Mutexes
Mutexes, short for mutual exclusion, are used to protect shared resources from being accessed simultaneously by multiple threads. C++ provides the std::mutex class for this purpose. A mutex can be locked and unlocked to create a critical section of code that only one thread can execute at a time.
#include <mutex>
std::mutex mtx;
void SomeFunction()
{
std::lock_guard<std::mutex> lock(mtx);
// Code accessing the shared resource
}
int main()
{
std::thread t1(SomeFunction);
std::thread t2(SomeFunction);
t1.join();
t2.join();
return 0;
}
Condition Variables
Condition variables allow threads to efficiently wait for a certain condition to be met before continuing their execution. C++ provides the std::condition_variable class for this purpose. Threads can wait on a condition variable until another thread notifies them of a change in the condition.
#include <condition_variable>
std::mutex mtx;
std::condition_variable cv;
bool condition = false;
void WaitForCondition()
{
std::unique_lock<std::mutex> lock(mtx);
cv.wait(lock, []{ return condition; });
// Code to execute after the condition is met
}
void NotifyCondition()
{
std::lock_guard<std::mutex> lock(mtx);
condition = true;
cv.notify_one();
}
int main()
{
std::thread t1(WaitForCondition);
std::thread t2(NotifyCondition);
t1.join();
t2.join();
return 0;
}
Atomic Operations
Atomic operations ensure that certain operations on shared variables are performed atomically without interruption. C++ provides the <atomic> header with various atomic types, such as std::atomic_int, std::atomic_bool, etc. Atomic operations can be used to update shared variables without the need for locks.
#include <atomic>
std::atomic_int counter(0);
void Increment()
{
counter++;
}
int main()
{
std::thread t1(Increment);
std::thread t2(Increment);
t1.join();
t2.join();
int result = counter;
return 0;
}
Conclusion
C++ provides various concurrency models and synchronization primitives to facilitate concurrent programming. Whether you prefer thread-based concurrency or task-based concurrency, or need to synchronize shared resources, C++ has you covered with its rich set of features. Understanding and utilizing these models and primitives can greatly enhance the performance and reliability of your concurrent programs.
References:
#concurrency #C++