Qt : How to start , stop and delete thread? - qt

Question

=====================OUTDATE=======================
I have a vector which contains threads, each thread is doing a while loop, for some reason, i need to delete the thread in the vector, to do this, i referenced this blog and write a test demo online. But when i write pthread_cancel() in Qt, it reports error: use of undeclared identifier 'pthread_cancel'. I have added LIBS += -lpthread in my .pro file and added #include <thread> in my .cpp file, this error still exists.
=====================UPDATE=====================
Afterwards, i trid to use QThread to achieve my goal. In brief, to start a qthread, i create a Worker class, then instantiate it and move it to QThread, connect &QThread::started with &Worker::process, process is the time consuming method, finnaly call thread->start();; to stop a qthread, i use a bool flag, and i store it with thread id in QMap, if the bool flag is set to false, qthread will break while loop, and emit a finished() signal and this signal will trigger &QThread::quit; to delete the qthread, i connect finished() signal with &Worker::deleteLater and &QThread::deleteLater.
The code are:
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "worker.h"
#include <QThread>
#include <QMap>
#include <QDebug>
QMap<int, bool> stateController;
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
ui->tableWidget->setSelectionBehavior(QAbstractItemView::SelectRows);
ui->tableWidget->setSelectionMode(QAbstractItemView::SingleSelection);
qDebug()<<"Main UI thread id is"<<(int)QThread::currentThreadId();
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_pushButton_add_clicked()
{
int row = ui->tableWidget->rowCount();
ui->tableWidget->insertRow(row);
ui->tableWidget->setItem(row,0,new QTableWidgetItem());//hold a place for blank item, in order to uniformly determine whether its text is empty afterwards
QTableWidgetItem *ckx = new QTableWidgetItem;
ckx->setCheckState(Qt::Unchecked);
ui->tableWidget->setItem(row,1,ckx);
}
void MainWindow::on_tableWidget_cellClicked(int row, int column)
{
if(column == 1){
bool state = ui->tableWidget->item(row,1)->checkState();
if(state){
if(ui->tableWidget->item(row,0)->text().isEmpty()){//only if there is not thread id, then create the thread
QThread* thread = new QThread();
qDebug()<<"New created thread id is"<<(int)thread->currentThreadId(); //I found this thread id will equal to main ui thread id, so i use a sigal/slot to update thread id
Worker* worker = new Worker(row);
worker->moveToThread(thread);
connect( worker, &Worker::updateQThreadIDSignal, this, &MainWindow::updateQThreadID);
connect( thread, &QThread::started, worker, &Worker::process);
connect( worker, &Worker::finished, thread, &QThread::quit);
// automatically delete thread and worker object when work is done:
connect( worker, &Worker::finished, worker, &Worker::deleteLater);
connect( thread, &QThread::finished, thread, &QThread::deleteLater);
//start the thread
thread->start();
}
}else{
if(!ui->tableWidget->item(row,0)->text().isEmpty()){//only if there is already the thread, then stop it
int thread_id = ui->tableWidget->item(row,0)->text().toInt();
// qDebug()<<"get thread id is"<<thread_id;
QMutexLocker locker(&mx);
stateController[thread_id] = false;
ui->tableWidget->setItem(row,0,new QTableWidgetItem());//Because thread will be delete later, so clear its thread id
}
}
}
}
void MainWindow::on_pushButton_delete_clicked()
{
QItemSelectionModel* selectionModel = ui->tableWidget->selectionModel();
QModelIndex index = selectionModel->currentIndex();
if(index.isValid()){
int row = index.row();
if(!ui->tableWidget->item(row,0)->text().isEmpty()){//Before stop the thread, ensure it exist
int thread_id = ui->tableWidget->item(row,0)->text().toInt();
if(ui->tableWidget->item(row,1)->checkState() == Qt::Checked){
//If not stopped yet, firstly stop it
QMutexLocker locker(&mx);
stateController[thread_id] = false;
}
stateController.remove(thread_id);
}
ui->tableWidget->removeRow(row);
}
}
void MainWindow::updateQThreadID(int row, QString id)
{
ui->tableWidget->setItem(row,0,new QTableWidgetItem(QString::number(id.toInt())));
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QMutex>
#include <vector>
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_pushButton_add_clicked();
void on_tableWidget_cellClicked(int row, int column);
void on_pushButton_delete_clicked();
public slots:
void updateQThreadID(int row, QString id);
private:
Ui::MainWindow *ui;
QMutex mx;
};
#endif // MAINWINDOW_H
worker.cpp
#include "worker.h"
#include <QThread>
#include <QDebug>
#include <QMutexLocker>
extern QMap<int, bool> stateController;
Worker::Worker(int row) : row_index(row) {
qDebug()<<"Create new worker at thread "<<(int)QThread::currentThreadId();
}
Worker::~Worker() {
qDebug()<<"Destroy the worker instance";
}
void Worker::process() {
thread_id = (int)QThread::currentThreadId();
stateController.insert(thread_id, true);
// qDebug()<<"set thread id is"<<thread_id;
emit updateQThreadIDSignal(row_index,QString("%1").arg(thread_id)); //execute once, because if delete row happen, the row index will change
while(true)
{
count++;
QThread::sleep(2);//simulate time consuming operations
qDebug()<<thread_id<<"processing"<<count;
{//life scope of locker
QMutexLocker locker(&mx);
if(!stateController[thread_id])//In every loop, determine whether it can run, if not, exit the loop
{
return;
}
}
}
emit finished();
}
worker.h
#ifndef WORKER_H
#define WORKER_H
#include <QObject>
#include <QMutex>
class Worker : public QObject {
Q_OBJECT
public:
Worker(int row);
~Worker();
public slots:
void process();
signals:
void finished();
void updateQThreadIDSignal(int, QString);
private:
int thread_id;
int row_index;
QMutex mx;
int count = 0;
};
#endif // WORKER_H
To watch the demo video, click here.
If you have any advice, please let me know, thanks !
Even though the codes seems to work fine, but i still have a question : Why i wrote &Worker::deleteLater, but I never see the destructor of Worker is called ?