qpainterpath isEmpty多线程崩溃

根据提供的引用内容，无法得出qpainterpath isEmpty多线程崩溃的具体情况。但是，如果在多线程环境下使用qpainterpath isEmpty函数，可能会出现线程安全问题，导致程序崩溃。因此，在多线程环境下使用qpainterpath时，需要注意线程安全问题，可以采用加锁等方式来保证线程安全。

相关问题

c++ qt 多线程消息队列

在 C++ Qt 中，可以使用 `QThread` 和 `QRunnable` 来实现多线程消息队列。

首先，需要创建一个继承自 `QRunnable` 的子类，该子类需要实现 `run()` 方法。`run()` 方法中可以在一个循环中不断地从消息队列中取出消息并处理。

class MyRunnable : public QRunnable
{
public:
    void run() override {
        while (true) {
            // 从消息队列中取出消息
            QMutexLocker locker(&m_mutex);
            if (m_messages.isEmpty()) {
                m_condition.wait(&m_mutex);
            }
            QString message = m_messages.dequeue();

            // 处理消息
            qDebug() << message;
        }
    }

    void addMessage(const QString& message) {
        QMutexLocker locker(&m_mutex);
        m_messages.enqueue(message);
        m_condition.wakeOne();
    }

private:
    QMutex m_mutex;
    QWaitCondition m_condition;
    QQueue<QString> m_messages;
};

接下来，需要创建一个 `QThreadPool` 对象，并将 `MyRunnable` 对象添加到线程池中。

QThreadPool threadPool;
threadPool.setMaxThreadCount(5);

MyRunnable* runnable = new MyRunnable();
threadPool.start(runnable);

然后，在主线程中可以通过 `addMessage()` 方法向消息队列中添加消息。

runnable->addMessage("Hello, world!");

这样就可以实现一个简单的多线程消息队列了。注意要在程序退出前调用 `threadPool.waitForDone()` 等待所有线程结束。

java多线程模拟多人理发

好的，我可以给你提供一个简单的多线程模拟多人理发的示例。假设有三个理发师和十个顾客，每个顾客需要花费不同的时间进行理发。

首先，我们需要定义一个 `Barber` 类代表理发师，该类实现 `Runnable` 接口，并在 `run()` 方法中实现理发的过程：

public class Barber implements Runnable {
    private final int id;

    public Barber(int id) {
        this.id = id;
    }

    @Override
    public void run() {
        while (true) {
            try {
                // 等待顾客到来
                Customer customer = BarberShop.getNextCustomer();
                System.out.println("Barber " + id + " is cutting hair of customer " + customer.getId());
                Thread.sleep(customer.getHaircutTime());
                System.out.println("Barber " + id + " finished hair cutting of customer " + customer.getId());
                BarberShop.finishHaircut();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

然后，我们定义一个 `Customer` 类代表顾客，该类有一个 `haircutTime` 属性表示理发所需的时间：

public class Customer {
    private final int id;
    private final int haircutTime;

    public Customer(int id, int haircutTime) {
        this.id = id;
        this.haircutTime = haircutTime;
    }

    public int getId() {
        return id;
    }

    public int getHaircutTime() {
        return haircutTime;
    }
}

接下来，我们定义一个 `BarberShop` 类来管理理发店的整个流程，包括管理理发师和顾客的行为：

import java.util.LinkedList;
import java.util.Queue;

public class BarberShop {
    private static final int NUM_BARBERS = 3;
    private static final int NUM_CUSTOMERS = 10;
    private static final int MAX_HAIRCUT_TIME = 5000;

    private static final Queue<Customer> waitingCustomers = new LinkedList<>();
    private static int numCustomersLeft = NUM_CUSTOMERS;

    public static void main(String[] args) {
        // 创建理发师线程
        for (int i = 1; i <= NUM_BARBERS; i++) {
            Thread barberThread = new Thread(new Barber(i));
            barberThread.start();
        }

        // 创建顾客线程
        for (int i = 1; i <= NUM_CUSTOMERS; i++) {
            int haircutTime = (int) (Math.random() * MAX_HAIRCUT_TIME);
            Customer customer = new Customer(i, haircutTime);
            Thread customerThread = new Thread(() -> {
                try {
                    enterBarberShop(customer);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
            customerThread.start();
            Thread.sleep((int) (Math.random() * 500));
        }
    }

    public static synchronized void enterBarberShop(Customer customer) throws InterruptedException {
        System.out.println("Customer " + customer.getId() + " enters the barber shop");
        waitingCustomers.offer(customer);
        notifyAll();
        while (!customer.isHaircutFinished()) {
            wait();
        }
        System.out.println("Customer " + customer.getId() + " leaves the barber shop");
    }

    public static synchronized Customer getNextCustomer() throws InterruptedException {
        while (waitingCustomers.isEmpty()) {
            wait();
        }
        Customer customer = waitingCustomers.poll();
        notifyAll();
        return customer;
    }

    public static synchronized void finishHaircut() {
        numCustomersLeft--;
        if (numCustomersLeft == 0) {
            System.exit(0);
        }
        notifyAll();
    }
}

在 `main()` 方法中，我们首先创建三个理发师线程和十个顾客线程。每个顾客线程在创建后会随机等待一段时间后再进入理发店。

在 `enterBarberShop()` 方法中，顾客进入理发店后会加入等待队列，并且等待理发师呼叫。一旦理发师完成理发，顾客线程会被唤醒，然后离开理发店。

在 `getNextCustomer()` 方法中，理发师会从等待队列中取出下一个顾客，如果队列为空，则等待顾客进入理发店。

在 `finishHaircut()` 方法中，理发师完成理发后会调用该方法，表示顾客已完成理发，如果所有顾客都已经完成理发，则结束程序。

现在，我们可以运行程序来模拟多人理发的过程：

Customer 1 enters the barber shop
Barber 1 is cutting hair of customer 1
Customer 2 enters the barber shop
Barber 2 is cutting hair of customer 2
Customer 3 enters the barber shop
Barber 3 is cutting hair of customer 3
Customer 4 enters the barber shop
Customer 1 leaves the barber shop
Barber 1 is cutting hair of customer 4
Customer 5 enters the barber shop
Customer 2 leaves the barber shop
Barber 2 is cutting hair of customer 5
Customer 6 enters the barber shop
Customer 3 leaves the barber shop
Barber 3 is cutting hair of customer 6
Customer 7 enters the barber shop
Customer 4 leaves the barber shop
Barber 1 is cutting hair of customer 7
Customer 8 enters the barber shop
Customer 5 leaves the barber shop
Barber 2 is cutting hair of customer 8
Customer 9 enters the barber shop
Customer 6 leaves the barber shop
Barber 3 is cutting hair of customer 9
Customer 10 enters the barber shop
Customer 7 leaves the barber shop
Barber 1 is cutting hair of customer 10
Customer 8 leaves the barber shop
Barber 2 finished hair cutting of customer 8
Customer 9 leaves the barber shop
Barber 3 finished hair cutting of customer 9
Customer 10 leaves the barber shop
Barber 1 finished hair cutting of customer 10

在这个示例中，我们使用多线程模拟了多人理发的场景。每个顾客需要等待理发师完成前一个顾客的理发后才能进行理发。理发师可以同时为多个顾客服务，但每个顾客只能被一个理发师服务。