Qt 線程等待條件

概念

??Qt提供了QWaitCondition類實現“等待條件”式的線程控制方法，它讓線程阻塞在等待條件的地方，直到條件滿足后才繼續執行下去。也就是說，QWaitCondition可以使一個線程在滿足一定條件時通知其他多個線程，使它們及時作出響應。
??QWaitCondition類成員函數

函數名稱	函數描述
QWaitCondition()	構造并初始化對象
wai()	解鎖互斥量，并阻塞等待喚醒條件
wakeAll()	喚醒所有處于等待狀態的線程，線程喚醒的順序不確定，由操作系統的調度策略決定
wakeOne()	喚醒一個處于等待狀態的線程，喚醒哪個線程不確定，由操作系統的調度策略決定
notify_all()	相當于wakeAll().此函數兼容STL
notify_one()	相當于wakeOne().此函數兼容STL

程序示例

讀取線程啟動進入等待喚醒狀態，當寫入數據線程寫入數據完成后喚醒所有讀取線程，讀取線程再繼續執行；

// 公共數據和鎖&等待喚醒對象
class TestData
{
public:static int sm_nSharedNumber;static QReadWriteLock sm_ReadWriteLock;static QWaitCondition sm_WaitCondition;
};int TestData::sm_nSharedNumber = 10;
QReadWriteLock TestData::sm_ReadWriteLock;
QWaitCondition TestData::sm_WaitCondition;// 寫入數據線程
class WorkThread2 : public QThread
{Q_OBJECT
public:explicit WorkThread2(QObject *parent = nullptr);~WorkThread2() = default;protected:void run() override;
};WorkThread2::WorkThread2(QObject *parent) : QThread(parent)
{}void WorkThread2::run()
{TestData::sm_ReadWriteLock.lockForWrite();TestData::sm_nSharedNumber += 5;TestData::sm_nSharedNumber *= 10;qDebug() << QString::fromLocal8Bit("write1 ----- 線程2 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;qDebug() << QString::fromLocal8Bit("write2 ----- 線程2 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;qDebug() << QString::fromLocal8Bit("write3 ----- 線程2 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;TestData::sm_WaitCondition.wakeAll();TestData::sm_ReadWriteLock.unlock();
}// 讀取數據線程
class WorkThread1 : public QThread
{Q_OBJECT
public:explicit WorkThread1(QObject *parent = nullptr);~WorkThread1() = default;protected:void run() override;};WorkThread1::WorkThread1(QObject *parent) : QThread(parent)
{}void WorkThread1::run()
{TestData::sm_ReadWriteLock.lockForRead();// 先解鎖 QReadWriteLock ，其他線程可以使用 QReadWriteLockTestData::sm_WaitCondition.wait(&TestData::sm_ReadWriteLock);qDebug() << QString::fromLocal8Bit("read1 ----- 線程1 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;msleep(10);qDebug() << QString::fromLocal8Bit("read2 ----- 線程1 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;msleep(20);qDebug() << QString::fromLocal8Bit("read3 ----- 線程1 ID:") << QThread::currentThreadId() << "Result = " << TestData::sm_nSharedNumber;TestData::sm_ReadWriteLock.unlock();
}// 測試函數
void Test()
{unique_ptr<WorkThread1> upThread11 = std::make_unique<WorkThread1>();unique_ptr<WorkThread1> upThread12 = std::make_unique<WorkThread1>();unique_ptr<WorkThread1> upThread13 = std::make_unique<WorkThread1>();unique_ptr<WorkThread2> upThread2 = std::make_unique<WorkThread2>();// 先啟動讀取函數，讓函數處在等待阻塞狀態upThread11->start();upThread12->start();upThread13->start();QThread::msleep(10);upThread2->start();upThread11->wait();upThread12->wait();upThread13->wait();upThread2->wait();qDebug() << "Over!";
}