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QT多线程全面讲解

news 2025/8/13 6:00:41

一、多线程基础概念

1.1 为什么需要多线程

提高响应性：主线程保持响应，耗时操作放入子线程
利用多核CPU：并行计算提高性能
模块化设计：不同功能在不同线程中运行

1.2 线程与进程的区别

进程：独立内存空间，系统资源分配的基本单位
线程：共享进程内存，CPU调度的基本单位，创建/切换开销小

二、QT多线程核心类

2.1 QThread

QT中线程的基础类，两种使用方式：

2.1.1 继承QThread方式

class WorkerThread : public QThread {Q_OBJECT
protected:void run() override {// 线程执行代码emit resultReady(result);}
signals:void resultReady(const QString &result);
};// 使用
WorkerThread *thread = new WorkerThread;
connect(thread, &WorkerThread::resultReady, this, &MyClass::handleResult);
connect(thread, &WorkerThread::finished, thread, &QObject::deleteLater);
thread->start();

2.1.2 moveToThread方式（推荐）

class Worker : public QObject {Q_OBJECT
public slots:void doWork(const QString ¶meter) {// 耗时操作emit resultReady(result);}
signals:void resultReady(const QString &result);
};// 使用
QThread *thread = new QThread;
Worker *worker = new Worker;
worker->moveToThread(thread);
connect(thread, &QThread::started, worker, []{ worker->doWork("data"); });
connect(worker, &Worker::resultReady, this, &MyClass::handleResult);
connect(thread, &QThread::finished, worker, &QObject::deleteLater);
connect(thread, &QThread::finished, thread, &QObject::deleteLater);
thread->start();

2.2 线程同步类

2.2.1 QMutex (互斥锁)

QMutex mutex;
int counter;void increment() {mutex.lock();counter++;mutex.unlock();
}// 更安全的方式：QMutexLocker
void safeIncrement() {QMutexLocker locker(&mutex);counter++;
}

2.2.2 QReadWriteLock (读写锁)

QReadWriteLock lock;
QString data;void readData() {QReadLocker reader(&lock);qDebug() << data;
}void writeData(const QString &newData) {QWriteLocker writer(&lock);data = newData;
}

2.2.3 QSemaphore (信号量)

QSemaphore sem(5); // 初始资源数5void acquireResource() {sem.acquire(); // 获取1个资源// 临界区操作sem.release(); // 释放资源
}

2.2.4 QWaitCondition (条件变量)

QMutex mutex;
QWaitCondition condition;
bool dataReady = false;void producer() {mutex.lock();// 生产数据dataReady = true;condition.wakeAll();mutex.unlock();
}void consumer() {mutex.lock();while (!dataReady) {condition.wait(&mutex);}// 消费数据dataReady = false;mutex.unlock();
}

三、线程间通信

3.1 信号槽机制

QT的核心特性，线程安全的通信方式：

// 主线程
connect(this, &MainWindow::startWork, worker, &Worker::doWork);
connect(worker, &Worker::resultReady, this, &MainWindow::handleResult);// 自动连接方式（默认）：
// 如果信号和槽在不同线程，会自动转为队列连接(QueuedConnection)

3.2 事件系统

// 自定义事件
class MyEvent : public QEvent {
public:static const QEvent::Type EventType = static_cast<QEvent::Type>(1000);MyEvent(const QString &data) : QEvent(EventType), m_data(data) {}QString data() const { return m_data; }
private:QString m_data;
};// 发送事件
QCoreApplication::postEvent(receiver, new MyEvent("data"));// 处理事件
bool Receiver::event(QEvent *e) {if (e->type() == MyEvent::EventType) {MyEvent *me = static_cast<MyEvent*>(e);// 处理事件return true;}return QObject::event(e);
}

四、线程池与高级特性

4.1 QThreadPool

管理线程的集合，避免频繁创建销毁线程

class Task : public QRunnable {void run() override {// 任务代码}
};// 使用
Task *task = new Task;
task->setAutoDelete(true); // 自动删除
QThreadPool::globalInstance()->start(task);

4.2 QtConcurrent

高级API，简化并行编程

4.2.1 Map-Reduce

QList<int> list = {1, 2, 3, 4, 5};// 并行map
QFuture<void> future = QtConcurrent::map(list, [](int &x) {x *= 2;
});// 并行map-reduce
QFuture<int> result = QtConcurrent::mappedReduced(list,[](int x) { return x * x; }, // map函数[](int &result, int value) { result += value; } // reduce函数
);result.waitForFinished();
qDebug() << "Sum of squares:" << result.result();

4.2.2 Filter

QList<int> list = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};QFuture<int> future = QtConcurrent::filtered(list, [](int x) {return x % 2 == 0; // 过滤偶数
});QList<int> evenNumbers = future.results();