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Qt 读写锁QReadWriteLock

news 2025/7/14 12:57:12

Qt 读写锁

QReadWriteLock

在基于互斥量QMutex的线程控制中，每次只能有一个线程获得互斥量的权限。如果在一个程序中有多个线程读取某个变量，使用互斥量时也必须排队。若只是读取一个变量，是可以让多个线程同时访问的，在这种只读的情况下，若仍然使用互斥量，就会降低程序的性能。

QReadWriteLock的特点：

读共享，写独占；
默认写锁优先级高于读锁优先级；

QReadWriteLock类的成员函数

函数名称	函数功能
QReadWriteLock()	构造读写锁对象
lockForRead()	以只读方式锁定资源，如果有其他线程以写入方式锁定，该函数会阻塞
lockForWrite()	以写入方式锁定资源，如果本线程或其他线程对读或写模式锁定资源，该函数就阻塞
unlock()	解读锁或解写锁
tryLockForRead()	lockForRead()的非阻塞版本。尝试请求读锁，可以设置超时时间
tryLockForWrite()	lockForWrite()的非阻塞版本。尝试请求写锁，可以设置超时时间

程序示例

一个线程写值，多个线程读取值的场景

// 公共数据和读写锁
class TestData
{
public:
    static int sm_nSharedNumber;
    static QReadWriteLock sm_ReadWriteLock;
};

int TestData::sm_nSharedNumber = 10;
QReadWriteLock TestData::sm_ReadWriteLock;

// 读取数据的线程类
class WorkThreadA : public QThread
{
    Q_OBJECT
public:
    explicit WorkThreadA(QObject *parent = nullptr);
    ~WorkThreadA() = default;

protected:
    void run() override;
};

WorkThreadA::WorkThreadA(QObject *parent) : QThread(parent)
{

}

void WorkThreadA::run()
{
    TestData::sm_ReadWriteLock.lockForRead();
    qDebug() << QString::fromLocal8Bit("read1 ----- 线程1 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;
    msleep(10);
    qDebug() << QString::fromLocal8Bit("read2 ----- 线程1 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;
    msleep(20);
    qDebug() << QString::fromLocal8Bit("read3 ----- 线程1 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;
    TestData::sm_ReadWriteLock.unlock();
}

// 写入数据的线程类
class WorkThreadB : public QThread
{
    Q_OBJECT
public:
    explicit WorkThreadB(QObject *parent = nullptr);
    ~WorkThreadB() = default;

protected:
    void run() override;

};

WorkThreadB::WorkThreadB(QObject *parent) : QThread(parent)
{

}

void WorkThreadB::run()
{
    TestData::sm_ReadWriteLock.lockForWrite();
    TestData::sm_nSharedNumber += 5;
    TestData::sm_nSharedNumber *= 10;

    qDebug() << QString::fromLocal8Bit("write1 ----- 线程2 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;
    qDebug() << QString::fromLocal8Bit("write2 ----- 线程2 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;
    qDebug() << QString::fromLocal8Bit("write3 ----- 线程2 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;
    TestData::sm_ReadWriteLock.unlock();
}

// 测试函数
void Test()
{
	// 创建了三个读取数据线程的对象
    unique_ptr<WorkThreadA> upThreadA1 = std::make_unique<WorkThreadA>();
    unique_ptr<WorkThreadA> upThreadA2 = std::make_unique<WorkThreadA>();
    unique_ptr<WorkThreadA> upThreadA3 = std::make_unique<WorkThreadA>();

	// 一个写入数据线程对象
    unique_ptr<WorkThreadB> upThreadB = std::make_unique<WorkThreadB>();

    upThreadA1->start();
    upThreadB->start();
    upThreadA2->start();
    upThreadA3->start();

    upThreadA1->wait();
    upThreadA2->wait();
    upThreadA3->wait();
    upThreadB->wait();
}