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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();
}