QT学习笔记：多线程操作

做了一个demo展示两种形式的多线程操作，第二种常用

1. new QThread Class & Override run()
2. new Object Class & moveToThread(new QThread)

// threadfirst.h  第一种形式的线程操作
#ifndef THREADFIRST_H
#define THREADFIRST_H

#include <QThread>
#include <QObject>

class ThreadFirst :  public QThread
{
    Q_OBJECT
public:
    explicit ThreadFirst(QObject *parent = nullptr);
    ~ThreadFirst();
protected:
    void run();
signals:
    void finish(const QString &str);
};

#endif // THREADFIRST_H

// threadfirst.cpp
#include "threadfirst.h"
#include <QDebug>
ThreadFirst::ThreadFirst(QObject *parent) :  QThread(parent)
{
}

ThreadFirst::~ThreadFirst()
{
}

void ThreadFirst::run()
{
    sleep(2);
    QString str = "threadFirst is finished";
    emit finish(str);
}

// threadsec.h  第二种形式的线程操作
#ifndef THREADSEC_H
#define THREADSEC_H
#include <QObject>
#include <QTimer>
class ThreadSec : public QObject
{
    Q_OBJECT
public:
    explicit ThreadSec();
    ~ThreadSec();
    void stopTimer();
signals:
    void finish();
private slots:
    void handleThread();
private:
    QTimer sigTimer; // 延时发出信号
};
#endif // THREADSEC_H
// threadsec.cpp
#include "threadsec.h"
ThreadSec::ThreadSec()
{
    connect(&sigTimer, &QTimer::timeout, this, &ThreadSec::handleThread);
    sigTimer.start(3000);
}
ThreadSec::~ThreadSec()
{

}
void ThreadSec::handleThread()
{
    emit finish();
}
void ThreadSec::stopTimer()
{
    sigTimer.stop();
}

主窗口类

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "threadfirst.h"
#include "threadsec.h"
#include <QThread>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:

    void on_btnFirst_clicked();

    void on_btnSec_clicked();

private:
    Ui::MainWindow *ui;
    ThreadFirst *_threadFirst = nullptr;
    ThreadSec *_threadSec = nullptr;
    QThread *_thread = nullptr;
};
#endif // MAINWINDOW_H

///
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}
MainWindow::~MainWindow()
{
    _threadFirst->quit();
    _threadFirst->wait();

    _thread->quit();
    _thread->wait();

    delete ui;
}
void MainWindow::on_btnFirst_clicked()
{
    _threadFirst = new ThreadFirst();
    connect(_threadFirst, &ThreadFirst::finished, _threadFirst, &QObject::deleteLater);
    connect(_threadFirst, &ThreadFirst::finish, this, [=] (QString str) {
        ui->lcdNumber->display(99);
        qDebug() << str;
    });
    _threadFirst->start();
}
void MainWindow::on_btnSec_clicked()
{
    int i = 0;
    _threadSec = new ThreadSec();
    _thread = new QThread();
    _threadSec->setObjectName("second use");
    _threadSec->moveToThread(_thread);
    connect(_thread, &QThread::finished, _threadSec, &QObject::deleteLater);
    connect(_threadSec, &ThreadSec::finish, this, [=] () mutable {
        ui->lcdNumber->display(i++);
        if (i >= 10) _threadSec->stopTimer();
        qDebug() << "threadSec is finished";
    });
    _thread->start();
}

• 问题：关于多线程同时访问同一个函数
  每个线程都有自己的栈区存放局部变量，不同线程调用函数的局部变量，保存在不同线程的栈区中，这种情况不需要进行互斥处理。
  需要进行互斥处理的情况通常是，函数中有全局变量，有动态申请的空间，静态变量，成员变量，或者是线程需要进行循环发送读取操作。