aca-tasks/task3/main-rd.cpp

#include <iostream>
#include <QSemaphore>
#include <QThread>
#include <QCoreApplication>

struct IPrintable {
    ~IPrintable() = default;

    virtual auto print() const -> void = 0;
};

class PrintA : public IPrintable {
private:
    QSemaphore &lockBC_;
public:
    explicit PrintA(QSemaphore &lockBc) : lockBC_(lockBc) {}

    auto print() const -> void override {
        this->lockBC_.release(1);
        std::cout << "A";
    }
};

class PrintB : public IPrintable {
private:
    QSemaphore &lockBC_;
    QSemaphore &lockC_;
public:
    explicit PrintB(QSemaphore &lockBc, QSemaphore &lockC) : lockBC_(lockBc), lockC_(lockC) {}

    auto print() const -> void override {
        if (this->lockBC_.tryAcquire(1)) {
            if (this->lockC_.available() == 0) {
                this->lockC_.release(1);
            }
            std::cout << "B";
        }
    }
};

class PrintC : public IPrintable {
private:
    QSemaphore &lockBC_;
    QSemaphore &lockC_;
public:
    explicit PrintC(QSemaphore &lockBc, QSemaphore &lockC) : lockBC_(lockBc), lockC_(lockC) {}

    auto print() const -> void override {
        if (this->lockBC_.tryAcquire(1)) {
            if (this->lockC_.tryAcquire(1)) {
                std::cout << "C";
            } else {
                this->lockBC_.release(1);
            }
        }
    }
};


template<typename T>
class Worker : public QThread {
private:
    std::unique_ptr<IPrintable> printer_;
public:
    template<typename ...Argts>
    Worker(QString tname, Argts &... args) : printer_(std::make_unique<T>(args...)) {};

protected:
    void run() {
        while (true) {
            printer_->print();
            std::cout.flush();
            sleep(1);
        }
    }
};


int main(int argc, char *argv[]) {

    QSemaphore lockC(1);
    QSemaphore lockBC(0);

    Worker<PrintA> t1("Thread 1", lockBC);
    Worker<PrintB> t2("Thread 1", lockBC, lockC);
    Worker<PrintC> t3("Thread 1", lockBC, lockC);

    t1.start();
    t2.start();
    t3.start();

    t1.wait();
    t2.wait();
    t3.wait();

    return 0;
}