Use and safe shutdown of qthread thread in QT

Preface

The first time I used threads, I couldn't achieve the desired effect , And to solve the problem of thread safe shutdown , Today, I saw a teacher talk about the use of threads , Although the understanding is not particularly profound , However, relevant precautions have been preliminarily summarized .

Environmental Science ：

• qt5.12.12
• windows operating system

Use thread thinking ：

1. New thread class , Inherit QThread
2. rewrite run() Method , Write complex programs in run In the implementation of , And set the cycle conditions （ Remember that some information says that threads must write loops ）
3. adopt start() Method to open the thread , adopt requestInterruption() Method sends an interrupt request to jump out of the loop condition , After jumping out of the loop, the thread ends
4. Set the signal slot in the process class , Kill the thread when it ends
5. In the destructor of the thread, you also need to add requestInterruption() Interrupt request , Prevent threads from closing safely when windows are forced to close

First list the weight lifting codes ：（ Remember to inherit classes QThread）

AudioThread.h file

void run() override;

AudioThread.cpp file

// Constructors 
AudioThread::AudioThread(QObject *parent) : QThread(parent)
{
    
    //  When the thread ends （finished）, Just call deleteLater Reclaiming memory 
    connect(this,&AudioThread::finished,this,[=](){
    
        this->deleteLater();
        qDebug()<<" Thread end ";
    });
}

// Destructor 
AudioThread::~AudioThread()
{
    
    // When forcing the window to close , Threads can also be safely shut down 
    requestInterruption();
    wait();
    qDebug()<<" Destructor ";
}

void AudioThread::run()
{
    
	..... Custom code 
    while(!isInterruptionRequested()){
    // When no interrupt request is sent , Execution loop body 
        ..... Custom code 
    }
    ..... Custom code 
}

Open thread ：

	AudioThread *audio_thread=new AudioThread(this);
    audio_thread->start();

Close thread ：

    audio_thread->requestInterruption();
    audio_thread->wait();	// Wait for the thread to end before executing the following code 
    audio_thread=nullptr;

Complete code ：（ I call here through thread ffmpeg Realize audio recording , It looks a little complicated , You can only focus on important code , Don't copy and paste blindly , You need to configure before running ffmpeg）

AudioThread.h file

#ifndef AUDIOTHREAD_H
#define AUDIOTHREAD_H

#include <QObject>
#include <QThread>

class AudioThread : public QThread
{
    
    Q_OBJECT
public:
    explicit AudioThread(QObject *parent = nullptr);
    ~AudioThread();

private:
    void run() override;
signals:

};

#endif // AUDIOTHREAD_H

AudioThread.cpp file

#include "audiothread.h"

#include <QDebug>
#include <QFile>

extern "C"{
    
//  Equipment related API
#include <libavdevice/avdevice.h>
//  Format dependent API
#include <libavformat/avformat.h>
//  Tool related API（ For example, error handling ）
#include <libavutil/avutil.h>
//  Code related API
#include <libavcodec/avcodec.h>
}


#ifdef Q_OS_WIN
    // PCM File name of the file 
    #define FILENAME "E:/media/out.pcm"
#else
    #define FILENAME "/Users/mj/Desktop/out.pcm"
#endif

AudioThread::AudioThread(QObject *parent) : QThread(parent)
{
    
    //  When the thread ends （finished）, Just call deleteLater Reclaiming memory 
    connect(this,&AudioThread::finished,this,[=](){
    
        this->deleteLater();
        qDebug()<<" Thread end ";
    });
}

AudioThread::~AudioThread()
{
    
    // When forcing the window to close , Threads can also be safely shut down 
    requestInterruption();
    wait();
    qDebug()<<" Destructor ";
}

void AudioThread::run()
{
    

    char *FMT_NAME="dshow";
    const AVInputFormat *localAv_find_input_format = av_find_input_format(FMT_NAME);
    if(!localAv_find_input_format){
    
        qDebug()<<" Input format not found "<<FMT_NAME;
        return;
    }
    qDebug()<<FMT_NAME;
    AVFormatContext *ctx=nullptr;
    char *device_name="audio= Microphone  (Realtek High Definition Audio)";
    int ret = avformat_open_input(&ctx,device_name,localAv_find_input_format,nullptr);
    if(ret!=0){
    
        char errbuf[1024];
        av_strerror(ret,errbuf,sizeof(errbuf));
        qDebug()<<" Failed to open device "<<ret<<errbuf;
        return;
    }

    QFile file(FILENAME);
    if(!file.open(QIODevice::WriteOnly)){
    
        qDebug()<<" File opening failure "<<FILENAME;
        avformat_close_input(&ctx);
        return;
    }

    AVPacket *pkt = av_packet_alloc();
    while(!isInterruptionRequested()){
    
        // Collect data 
        ret = av_read_frame(ctx,pkt);

        if(ret==0){
    
            // Write... To the document 
            file.write((char *)pkt->data,pkt->size);
            qDebug()<<" Recording in progress , File is being written ";

            // Release resources 
            av_packet_unref(pkt);
        }else if (ret == AVERROR(EAGAIN)) {
     //  Resources temporarily unavailable 
            continue;
        }
        else{
    
            char errbuf[1024];
            av_strerror(ret,errbuf,sizeof(errbuf));
            qDebug()<<"av_read_frame error "<<errbuf<<sizeof (errbuf);
            return;
        }
        av_packet_unref(pkt);
    }

    file.close();
    // Release resources 
    av_packet_free(&pkt);
    // Turn off the device 
    avformat_close_input(&ctx);
    qDebug()<<" Recording completed successfully ";

    return;
}

The main thread calls the sub thread ：（ You need to define global variables in advance AudioThread *audio_thread=nullptr;bool is_record,is_abnormal;）

void MainWindow::on_pushButton_clicked()
{
    
	if(!is_record){
    
        audio_thread=new AudioThread(this);
        audio_thread->start();
        // Prevent forced closing of windows , The thread cannot exit normally 
        connect(audio_thread,&AudioThread::finished,audio_thread,[=](){
    
            ui->pushButton->setText(" Start recording ");
            is_record=false;
            if(is_abnormal){
    
                qDebug()<<" Thread ended abnormally ";
            }
        });
        qDebug()<<" Start recording ";
        ui->pushButton->setText(" The end of the recording ");
        is_record=true;
    }else{
    
        is_abnormal=false;
        audio_thread->requestInterruption();
        audio_thread->wait();
        audio_thread=nullptr;
        qDebug()<<" The end of the recording ";
        ui->pushButton->setText(" Start recording ");
        is_record=false;
    }
}

Program effect ：

Feeling QThread There are still many precautions in use , There will be new understandings in the future

It's not easy to code words , If this blog is helpful to you , Please praise the collection , Thank you very much ！ There is something wrong