1. Method of interprocess communication

1. TCP/IP
   Qt Network It provides many classes to realize network programming .
2. Shared memory
   QSharedMemory Is a cross platform shared memory class , Provides the implementation of accessing the shared memory of the operating system . It allows multiple threads and processes to safely access shared memory fragments . Besides ,QSystemSemaphore It can be used to control the access of shared resources and inter process communication of the system .
3. D-Bus
   D-Bus The module is a Unix library , have access to D-Bus Protocol to realize interprocess communication . It will Qt The signal and slot mechanism is extended to IPC level , Allows a signal emitted by one process to be associated with another process's slot .
4. QProcess
5. session management
   stay Linux/X11 On the platform ,Qt Provides support for session management , The reply allows time to propagate to the process . for example , Notify processes or programs when shutdown , So you can perform some related operations .

2. Sample code of shared memory between different processes

• dialog.h

#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>
#include <QSharedMemory>

namespace Ui {
    
class Dialog;
}

class Dialog : public QDialog
{
    
    Q_OBJECT

public:
    explicit Dialog(QWidget *parent = 0);
    ~Dialog();

private:
    Ui::Dialog *ui;
    QSharedMemory sharedMemory;

    void detach();

public slots:
    void loadFromFile();
    void loadFromMemory();
private slots:
    void on_pushButtonLoadFromFile_clicked();
    void on_pushButtonLoadFromSharedMemory_clicked();
};

#endif // DIALOG_H

• dialog.cpp

#include "dialog.h"
#include "ui_dialog.h"
#include <QFileDialog>
#include <QBuffer>
#include <QDebug>

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    
    ui->setupUi(this);
    // Before sharing memory , You need to develop a key, The system uses it as the identification of the underlying shared memory segment . This key Can be any string 
    sharedMemory.setKey("QSharedMemoryExample");
}

Dialog::~Dialog()
{
    
    delete ui;
}

void Dialog::loadFromFile()
{
    
    // Determine whether the process is connected to the shared memory segment , If it is , Separate the process from the shared memory segment .
    if(sharedMemory.isAttached())
        detach();

    ui->label->setText(tr(" Select a picture file ！"));
    QString fileName = QFileDialog::getOpenFileName(0,QString(),QString(),tr("Images(*.png *.jpg)"));
    QImage image;
    if(!image.load(fileName))
    {
    
        ui->label->setText(tr(" The selected file is not a picture , Please select a picture file "));
        return;
    }
    ui->label->setPixmap((QPixmap::fromImage(image)));
    // Load pictures into shared memory 
    QBuffer buffer;
    // Save pictures to buffer in 
    buffer.open(QBuffer::ReadWrite);
    // Get the pointer of picture data 
    QDataStream out(&buffer);
    out<<image;
    // Get the size of the picture 
    int size = buffer.size();
    // Create a shared memory segment of the specified size 
    if(!sharedMemory.create(size))
    {
    
        ui->label->setText(tr(" Unable to create shared memory segment "));//
        return;
    }
    // During the operation of shared memory segment , It needs to be locked first 
    sharedMemory.lock();
    char * to = (char*)sharedMemory.data();
    const char * from = buffer.data().data();
    memcpy(to,from,qMin(sharedMemory.size(),size));
    // Unlock 
    sharedMemory.unlock();

    // If you separate the last process connected to the shared memory segment , Then the system will release the shared memory segment .
}

void Dialog::loadFromMemory()
{
    
    // Connect the process to the shared memory segment 
    if(!sharedMemory.attach())
    {
    
        ui->label->setText(tr(" Unable to connect to shared memory segment ,\n"
                              " Please load a picture first ！"));
        return;
    }
    QBuffer buffer;
    QDataStream in(&buffer);
    QImage image;
    sharedMemory.lock();
    // Read the data in the memory segment 
    buffer.setData((char*)sharedMemory.constData(),sharedMemory.size());
    buffer.open(QBuffer::ReadOnly);
    in>>image;
    sharedMemory.unlock();
    sharedMemory.detach();
    ui->label->setPixmap(QPixmap::fromImage(image));

}
void Dialog::detach()
{
    
    if(!sharedMemory.detach())
    {
    
        ui->label->setText(tr(" Cannot detach from shared memory "));
    }
}

void Dialog::on_pushButtonLoadFromFile_clicked()
{
    
    loadFromFile();
}

void Dialog::on_pushButtonLoadFromSharedMemory_clicked()
{
    
    loadFromMemory();
}