c++ cyclic barrier

Certainly! Here's an example of a cyclic barrier in C++ with explanations for each step:

#include <iostream>
#include <mutex>
#include <condition_variable>

class CyclicBarrier {
public:
    explicit CyclicBarrier(int parties) : parties_(parties), count_(parties), generation_(0) {}

    void await() {
        std::unique_lock<std::mutex> lock(mutex_);
        int gen = generation_;

        if (--count_ == 0) {
            // Last thread to arrive, reset count for next generation
            count_ = parties_;
            ++generation_;
            cv_.notify_all();
        } else {
            // Wait until the generation changes
            cv_.wait(lock, [this, gen] { return gen != generation_; });
        }
    }

private:
    std::mutex mutex_;
    std::condition_variable cv_;
    int parties_;
    int count_;
    int generation_;
};

// Example usage
void worker(int id, CyclicBarrier& barrier) {
    std::cout << "Worker " << id << " started" << std::endl;
    // Simulate work
    // ...

    barrier.await();

    std::cout << "Worker " << id << " finished" << std::endl;
}

int main() {
    const int num_threads = 4;
    CyclicBarrier barrier(num_threads);

    // Start worker threads
    std::thread threads[num_threads];
    for (int i = 0; i < num_threads; ++i) {
        threads[i] = std::thread(worker, i, std::ref(barrier));
    }

    // Join threads
    for (int i = 0; i < num_threads; ++i) {
        threads[i].join();
    }

    return 0;
}

Explanation:

1. CyclicBarrier Class: Implements a cyclic barrier synchronization primitive.
2. Constructor: Initializes the barrier with the given number of parties (threads).
3. await(): Method called by each thread to wait at the barrier.
4. Mutex and Condition Variable: Used for thread synchronization and signaling.
5. Parties, Count, and Generation: Keep track of the number of parties, the count of arrived threads, and the barrier generation.
6. await() Method Explanation:
7. Acquires a lock.
8. Checks the current generation and decrements the count of arrived threads.
9. If the current thread is the last one to arrive, it resets the count for the next generation and notifies all waiting threads.
10. Otherwise, it waits until the generation changes using the condition variable.
11. Worker Function: Simulates work and waits at the barrier.
12. Main Function:
13. Creates a CyclicBarrier object and multiple worker threads.
14. Starts the worker threads and waits for them to complete by joining them.

This implementation demonstrates how the cyclic barrier allows multiple threads to synchronize at a predefined point in the code.