Qt笔记-多线程检索数据库（单例多重锁，QtConcurrent::blockingMapped）

超、凢脫俗 2022-12-07 04:25 80阅读 0赞

这里主要是个事例，并不涉及业务逻辑处理。在此记录下。

程序运行截图如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxNzg0NDI3NjE_size_16_color_FFFFFF_t_70][]

这里有下面这个类BigDataTest对数据进行的类。

MySQLInstance采用单例双重锁模式对数据库进行操作。

源码如下：

BigDataTest.h

#ifndef CONCURRENT_H
    #define CONCURRENT_H
    
    #include <QObject>
    #include <QList>
    
    
    class BigDataTest : public QObject
    {
        Q_OBJECT
    public:
        BigDataTest(QObject *parent = 0);
        void run();
    
    protected:
        bool connectMySQL();
        friend QString sqlResult(const QString &cmd);
    
    private:
        QList<QString> m_str;
    };
    
    #endif // CONCURRENT_H

MySQLInstance.h

#ifndef MYSQLINSTANCE_H
    #define MYSQLINSTANCE_H
    
    #include <QSqlDatabase>
    
    class MySQLInstance
    {
    public:
        static MySQLInstance *getInstance();
        QString execSql(const QString &cmd);
    
    protected:
        MySQLInstance();
        void connectMySQL();
    
    private:
        static MySQLInstance *m_instance;
        QSqlDatabase m_db;
    };
    
    #endif // MYSQLINSTANCE_H

BigDataTest.cpp

#include "BigDataTest.h"
    #include "MySQLInstance.h"
    #include <QDebug>
    #include <QtConcurrent>
    #include <QSqlQuery>
    
    BigDataTest::BigDataTest(QObject *parent) : QObject(parent)
    {
    
        m_str << "SELECT 1 + 1" << "SELECT 100 * 100 * 100 / 10" << "SELECT 100 + 99" << "SELECT 1 + 1"
              << "SELECT 1 + 1 + 500" << "SELECT 1 + 1 + 1000" << "SELECT 1999 - 199" << "SELECT 1999 + 10"
              << "SELECT 1 + 1 + 8888" << "SELECT 1 + 1 + 788";
    }
    
    QString sqlResult(const QString &cmd)
    {
        qDebug() << "处理SQL语句进程 : " << QThread::currentThread();
        MySQLInstance *instance = MySQLInstance::getInstance();
        return instance->execSql(cmd);
    }
    
    
    void BigDataTest::run()
    {
        QList<QString> retList = QtConcurrent::blockingMapped(m_str, sqlResult);
        qDebug() << "返回结果";
        qDebug() << retList;
    }

main.cpp

#include <QCoreApplication>
    #include "BigDataTest.h"
    
    int main(int argc, char *argv[])
    {
        QCoreApplication a(argc, argv);
    
        BigDataTest bigDataTest;
        bigDataTest.run();
    
        return a.exec();
    }

MySQLInstance.cpp

#include "MySQLInstance.h"
    #include <QSqlQuery>
    #include <QSqlError>
    #include <QDebug>
    #include <QMutex>
    #include <QVariant>
    
    MySQLInstance *MySQLInstance::m_instance = nullptr;
    QMutex mt;
    
    MySQLInstance *MySQLInstance::getInstance()
    {
        if(m_instance == nullptr){
    
            mt.lock();
            if(m_instance == nullptr){
    
                m_instance = new MySQLInstance();
                mt.unlock();
                return m_instance;
            }
            mt.unlock();
        }
    
        return m_instance;
    }
    
    QString MySQLInstance::execSql(const QString &cmd)
    {
        if(m_instance == nullptr){
    
            Q_ASSERT(!"m_instance == nullptr");
        }
    
    
        //简单点，返回值只有一个
        mt.lock();
        QSqlQuery query(m_db);
        if(!query.exec(cmd)){
    
            mt.unlock();
            qDebug() << "error:" << query.lastError().text();
            return "error";
        }
        mt.unlock();
    
        QString ret = "none";
        while(query.next()){
    
            ret = query.value(0).toString();
        }
    
    
        return ret;
    }
    
    MySQLInstance::MySQLInstance()
    {
        connectMySQL();
    }
    
    void MySQLInstance::connectMySQL()
    {
        m_db = QSqlDatabase::addDatabase("QMYSQL");
        m_db.setHostName("127.0.0.1");
        m_db.setPort(3306);
        m_db.setDatabaseName("mysql");
        m_db.setUserName("root");
        m_db.setPassword("root");
        m_db.open();
    }

程序打包下载地址：

[https://github.com/fengfanchen/Qt/tree/master/DealWithBigData][https_github.com_fengfanchen_Qt_tree_master_DealWithBigData]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxNzg0NDI3NjE_size_16_color_FFFFFF_t_70]: /images/20221123/e43207bef8e34f039b860bf1e9731b4f.png
[https_github.com_fengfanchen_Qt_tree_master_DealWithBigData]: https://github.com/fengfanchen/Qt/tree/master/DealWithBigData