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

class ProducerConsumer {
private:
    int value; // 1
    bool produced; // 2
    mutex m;
	condition_variable cv;

public:
	ProducerConsumer(): value(-1), produced(false) {}

	void producer(unsigned int count) {
        for(int i = count; i >= 0; --i) {
            unique_lock<mutex> l(m);
            cv.wait(l, [this](){ return !produced; } ); // 1

            cout << "Producer sets value to " << i << endl;
            value = i;
            produced = true;
            cv.notify_one(); // 2
        }
    }

	void consumer() {
	    do {
            unique_lock<mutex> l(m);
            cv.wait(l, [this](){ return produced; } );

            cout << "Consumer now is in control: " << value << endl;
            produced = false;
            cv.notify_one();
        } while(value);
	}
};

int main() {
	// your code goes here

	ProducerConsumer p;
	thread t1(&ProducerConsumer::consumer, &p);
	thread t2(&ProducerConsumer::producer, &p, 2);

	t1.join();
	t2.join();

	return 0;
}

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

/* Question:

*/

class ProducerConsumer {
private:
	int value; // 1 
	bool produced; // 2 
	mutex m;
	condition_variable cv;	

public:
	ProducerConsumer() : value(-1), produced(false) {}

	void producer(unsigned int count) {
		for (int i = count; i >= 0; --i) {
			unique_lock<mutex> l(m);
			cv.wait(l, [this](){ return !produced; }); // 1 

			cout << "Producer sets value to " << i << endl;

			value = i;
			produced = true;
			cv.notify_one(); // 2 
		}
	}

	void consumer(unsigned int thread_id) {
		do {
			unique_lock<mutex> l(m);
			cv.wait(l, [this](){ return produced; });

			cout << "Consumer thread " << thread_id << "...now is in control: " << value << endl;
			produced = false;
			cv.notify_one();
		} while (value);

		cout << thread_id << endl;
	}
};

int main() {
	// your code goes here 

	ProducerConsumer p;
	thread t1(&ProducerConsumer::consumer, &p, 1);
	thread t2(&ProducerConsumer::consumer, &p, 2);
	thread t3(&ProducerConsumer::producer, &p, 3);

	t3.join();
	t1.join();
	t2.join();

	return 0;
}

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

/* Question:

*/

class ProducerConsumer {
private:
	int value; // 1 
	bool produced; // 2 
	mutex lock;
	mutex m;
	condition_variable cv;

public:
	ProducerConsumer() : value(-1), produced(false) {}

	void producer(unsigned int count) {
		for (int i = count; i >= 0; --i) {
			{
				unique_lock<mutex> l(lock);
				cv.wait(l, [this](){ return !produced; }); // 1
			}

			{
				unique_lock<mutex> l(m);
				cout << "Producer sets value to " << i << endl;
			}

			value = i;
			produced = true;
			cv.notify_one(); // 2 
		}
	}

	void consumer(unsigned int thread_id) {
		do {
			bool exit_loop = false;

			{
				unique_lock<mutex> l(lock);

				if (!cv.wait_for(l, std::chrono::milliseconds(500), [this](){ return produced; })) {
					std::cerr << "Thread " << thread_id << " finished waiting" << endl;
					exit_loop = true;
					break;
				}
			}

			if (exit_loop) {
				break;
			}

			{
				unique_lock<mutex> l(m);
				cout << "Consumer thread " << thread_id << "...now is in control: " << value << endl;
			}

			produced = false;
			cv.notify_one();

			std::this_thread::sleep_for(std::chrono::milliseconds(10));
		} while (value);
	}
};

int main() {
	// your code goes here 

	ProducerConsumer p;
	thread consumer_thread1(&ProducerConsumer::consumer, &p, 1);
	thread consumer_thread2(&ProducerConsumer::consumer, &p, 2);
	thread producer_thread(&ProducerConsumer::producer, &p, 10);

	producer_thread.join();
	consumer_thread1.join();
	consumer_thread2.join();

	cout << "\nThreads successfully completed..." << endl;

	return 0;
}

Producer sets value to 10
Consumer thread 2...now is in control: 10
Producer sets value to 9
Consumer thread 1...now is in control: 9
Consumer thread 2...now is in control: 9
Producer sets value to 8
Consumer thread 1...now is in control: 8
Consumer thread 2...now is in control: 8
Producer sets value to 7
Consumer thread 1...now is in control: 7
Producer sets value to 6
Consumer thread 2...now is in control: 6
Producer sets value to 5
Consumer thread 1...now is in control: 5
Producer sets value to 4
Consumer thread 2...now is in control: 4
Producer sets value to 3
Consumer thread 1...now is in control: 3
Producer sets value to 2
Consumer thread 2...now is in control: 2
Producer sets value to 1
Consumer thread 1...now is in control: 1
Producer sets value to 0
Consumer thread 2...now is in control: 0

Threads successfully completed...

...warum bekommen jetzt manchmal 2 consumer threads gleichzeitig access?

Der unique_lock (Z.45) ist nur in dem scope in dem er definiert ist wirksam (Z.45 - 52). Der zweite lock (m) ist überflüssig, doppelt hält nicht besser