What are the cooperation mechanisms of C++ functions in concurrent programming?

C Concurrent programming provides collaboration mechanisms, including mutexes, condition variables, semaphores and atomic variables, to coordinate thread interactions and prevent conflicts and deadlocks. These mechanisms include: Mutexes: Protect shared resources, ensuring access by only one thread at a time. Condition variable: Allows a thread to wait for a condition to be met and be notified. Semaphores: Limit the number of threads that can access shared resources at the same time. Atomic variables: Ensure atomic operations on shared variables and prevent data competition.

The collaboration mechanism of C functions in concurrent programming

In concurrent programming, the collaboration mechanism allows multiple functions to work together. without causing conflicts or deadlocks. C provides a variety of cooperative mechanisms designed to improve the scalability and efficiency of concurrent applications.

Mutex (Mutex)

A mutex is a variable that protects a shared resource from simultaneous access. It ensures that only one thread can access a protected resource by acquiring and releasing locks.

std::mutex m;

void thread_function() {
  // 获得互斥量锁
  m.lock();

  // 访问共享资源

  // 释放互斥量锁
  m.unlock();
}

Condition Variable

Condition variable is used to wait for a certain condition to be met. It can wait for the condition to become true through the wait() function, or notify the waiting thread through the notify_one() or notify_all() function.

std::condition_variable cv;
std::mutex m;
bool condition_met = false;

void waiting_thread_function() {
  std::unique_lock<std::mutex> lock(m);
  while (!condition_met) {
    cv.wait(lock);
  }
}

void signalling_thread_function() {
  std::lock_guard<std::mutex> lock(m);
  condition_met = true;

  // 通知等待的线程
  cv.notify_all();
}

Semaphore

Semaphore is used to limit the number of threads that can access shared resources at the same time. It is implemented through a counter that represents the number of threads that can access the resource simultaneously.

std::counting_semaphore<int> semaphore(2);

void thread_function() {
  // 获取许可证，允许访问资源
  semaphore.acquire();

  // 访问共享资源

  // 释放许可证
  semaphore.release();
}

Atomic Variable

Atomic variable is a special variable type that guarantees atomic access to shared variables. It uses specific hardware instructions to ensure that the read and write operations of variables are indivisible, thereby preventing data races.

std::atomic<int> counter = 0;

void thread_function() {
  // 原子增加计数器
  counter.fetch_add(1);
}

Practical case: producer-consumer problem

The producer-consumer problem is a classic problem in concurrent programming, involving producer threads and consumers thread. Producer threads produce and insert elements into a shared queue, while consumer threads remove elements from the queue and consume them.

Using the above collaboration mechanism, we can solve this problem safely and reliably:

• Use a mutex to protect the queue and prevent simultaneous access.
• Use condition variables to notify consumers that there are new elements in the queue.
• Use semaphores to limit the number of consumer threads that can consume elements at the same time.

By combining these collaborative mechanisms, we can create efficient and lock-free producer-consumer implementations.

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