I have a QThread that starts an external Linux binary. I use connect() to call a slot(), which is part of the QThread, whenever I get an output from that external Linux binary. This seems not to work for me. Can anyone tell me what is wrong in the below code?
class ThreadPowerSubSystem : public QThread
{
public:
ThreadPowerSubSystem(){ }
private slots:
void checkForTwoSecPress()
{
qWarning("button pressed");
}
private:
void run()
{
QProcess *powerProcess = new QProcess();
powerProcess->start("/home/testApp/button");
connect(powerProcess, SIGNAL(readyRead()), this, SLOT(checkForTwoSecPress()));
exec();
}
};
Also I need to call a function to display a dialog inside that slot. Can anyone show me an example on how to do it?
Related
I have a program which has class MainWindow that inherited from QMainWindow.
I want to run a specific function in a new thread.
Since I can't inherit from QThread so the best solution is to use QtConcurrent.
I stored QtConcurrent result in a QFuture but as mentioned in the QT documentation, the result of QtConcurrent can not be canceled by QFuture::cancel.
I see some questions like mine but the answers are to create a class which inherit from QThread that I can't.
So what is the solution?
Here is my codes:
mainwindow.h:
using namespace std;
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
...
private:
Ui::MainWindow *ui;
...
QFuture<void> future;
QFutureWatcher< void > futureWatcher;
QPushButton *stop_pushButton_=new QPushButton;
private slots:
...
void on_graph_pushButton_clicked();
void generateGraph();
void stopPushButtonClicked();
};
mainwindow.cpp:
void MainWindow::stopPushButtonClicked()
{
futureWatcher.setFuture(future);
futureWatcher.cancel();
futureWatcher.waitForFinished();
}
...
void MainWindow::on_graph_pushButton_clicked()
{
loadingOn();
future = QtConcurrent::run(this,&MainWindow::generateGraph);
}
void MainWindow::generateGraph()
{
InsertLogs::getInstance()->printStatus(USER_GENERATE_GRAPH);
GenGraph* gr=new GenGraph;
connect(this,&MainWindow::loadingOffSignal,this,&MainWindow::loadingOff);
graphType_=gr->generateGraph(persons_comboBox_->currentText(),
ui->graphResource1_comboBox->currentText(),
ui->graphResource2_comboBox->currentText(),
ui->graphType_comboBox->currentText());
InsertLogs::getInstance()->printSuccess(SYSTEM_GENERATE_GRAPH);
emit loadingOffSignal();
}
When I click on graph_pushButton, generatedGraph is called in a new thread, but when I click on stop_pushButton the future does not stop and the generatedGraph function executes completely.
I'm currently trying to make a software that downloads a lot of files from Google Drive. Downloading is currently not a problem.
Nevertheless, I encounter an issue when launching 500+ simultaneous downloads. I use a slightly modified version of this tutorial : https://wiki.qt.io/Download_Data_from_URL.
Here is the .h file :
class FileDownloader : public QObject
{
Q_OBJECT
public:
explicit FileDownloader(QUrl url, QObject *parent = 0, int number = 0);
QByteArray downloadedData() const;
void launchNewDownload(QUrl url);
QByteArray m_DownloadedData;
QNetworkReply* reply;
static QNetworkAccessManager *m_WebCtrl;
signals:
void downloaded();
private slots:
void fileDownloaded(QNetworkReply* pReply);
};
And here is the .cpp file :
QNetworkAccessManager* FileDownloader::m_WebCtrl = nullptr;
FileDownloader::FileDownloader(QUrl url, QObject *parent) :
QObject(parent)
{
if (m_WebCtrl == nullptr) {
m_WebCtrl = new QNetworkAccessManager(this);
}
connect(m_WebCtrl, SIGNAL (finished(QNetworkReply*)),this, SLOT (fileDownloaded(QNetworkReply*)));
launchNewDownload(url);
}
void FileDownloader::launchNewDownload(QUrl url) {
QNetworkRequest request(url);
this->reply = m_WebCtrl->get(request);
}
void FileDownloader::fileDownloaded(QNetworkReply* pReply) {
m_DownloadedData = pReply->readAll();
//emit a signal
pReply->deleteLater();
emit downloaded();
}
QByteArray FileDownloader::downloadedData() const {
return m_DownloadedData;
}
The issue is "QThread::start: Failed to create thread ()" when reaching about the 500th download. I tried to limit the number of downloads which run at the same time - but I always get the same issue. Besides, I tried to delete every downloader when finishing its task - it did nothing else than crashing the program ;)
I think that it is coming from the number of threads allowed for an only process, but I'm not able to solve it !
Does anyone have an idea that could help me ?
Thank you !
QNetworkAccessManager::finished signal is documented to be emitted whenever a pending network reply is finished.
This means that if the QNetworkAccessManager is used to run multiple requests at a time (and this is perfectly normal usage). finished signal will be emitted once for every request. Since you have a shared instance of QNetworkAccessManager between your FileDownloader objects, the finished signal gets emitted for every get call you have made. So, all the FileDownloader objects get a finished signal as soon as the first FileDownloader finishes downloading.
Instead of using QNetworkAccessManager::finished, you can use QNetworkReply::finished to avoid mixing up signals. Here is an example implementation:
#include <QtNetwork>
#include <QtWidgets>
class FileDownloader : public QObject
{
Q_OBJECT
//using constructor injection instead of a static QNetworkAccessManager pointer
//This allows to share the same QNetworkAccessManager
//object with other classes utilizing network access
QNetworkAccessManager* m_nam;
QNetworkReply* m_reply;
QByteArray m_downloadedData;
public:
explicit FileDownloader(QUrl imageUrl, QNetworkAccessManager* nam,
QObject* parent= nullptr)
:QObject(parent), m_nam(nam)
{
QNetworkRequest request(imageUrl);
m_reply = m_nam->get(request);
connect(m_reply, &QNetworkReply::finished, this, &FileDownloader::fileDownloaded);
}
~FileDownloader() = default;
QByteArray downloadedData()const{return m_downloadedData;}
signals:
void downloaded();
private slots:
void fileDownloaded(){
m_downloadedData= m_reply->readAll();
m_reply->deleteLater();
emit downloaded();
}
};
//sample usage
int main(int argc, char* argv[]){
QApplication a(argc, argv);
QNetworkAccessManager nam;
FileDownloader fileDownloader(QUrl("http://i.imgur.com/Rt8fqpt.png"), &nam);
QLabel label;
label.setAlignment(Qt::AlignCenter);
label.setText("Downloading. . .");
label.setMinimumSize(640, 480);
label.show();
QObject::connect(&fileDownloader, &FileDownloader::downloaded, [&]{
QPixmap pixmap;
pixmap.loadFromData(fileDownloader.downloadedData());
label.setPixmap(pixmap);
});
return a.exec();
}
#include "main.moc"
If you are using this method to download large files, consider having a look at this question.
One solution could be to uses a QThreadPool. You simply feed it tasks (QRunnable) and it will handle the number of threads and the task queue for you.
However in your case this is not perfect because you will be limiting the number of simultaneous downloads to the number of threads created by QThreadPool (generally the number of CPU core you have).
To overcome this you will have to handle the QThread yourself and not use QThreadPool. You would create a small number of thread (see QThread::idealThreadCount()) and run multiple FileDownloader on each QThread.
I have a MainForm class (as you'd expect, it is a form) that has a text box on it. I also have another class called 'Application_Server' That does a load of other stuff (not just form-background related, quite a lot of network based stuff etc.).
The Application_Server class runs in it's own thread, but needs to be able to update the controls on the form, for this question, we will stick with just the textbox.
The problem is that even though I am executing the command to set the text of the textBox control via 'Invoke' I am still getting the following exception during runtime:
Additional information: Cross-thread operation not valid: Control
'DebugTextBox' accessed from a thread other than the thread it was
created on.
What could be causing this? I am definitely invoking a delegate within MainForm.
Here are the relevant code segments (cut down for readability):
MainForm.h:
public ref class MainForm : public System::Windows::Forms::Form {
delegate void del_updateDebugText(String^ msg);
del_updateDebugText^ updateDebugText = gcnew del_updateDebugText(this, &MainForm::postDebugMessage);
private: void postDebugMessage(String^ message);
};
MainForm.cpp:
void EagleEye_Server::MainForm::postDebugMessage(String^ message)
{
Monitor::Enter(DebugTextBox);
if (this->DebugTextBox->InvokeRequired)
{
this->Invoke(updateDebugText, gcnew array<Object^> { message });
}
else
{
this->DebugTextBox->AppendText(message);
}
Monitor::Exit(DebugTextBox);
}
And finally, the code calling it:
void ServerAppManager::postDebugMessage(System::String^ message)
{
mainFormHandle->updateDebugText(message);
}
void ServerAppManager::applicationStep()
{
postDebugMessage("Starting\n");
// This is Run in seperate thread in MainForm.cpp
while (s_appState == ApplicationState::RUN)
{
postDebugMessage("Testing\n");
}
}
Thanks!
From background worker called bwSearch we do the call as following from the DoWork event handler:
private: System::Void bwSearch_DoWork(System::Object^ sender, System::ComponentModel::DoWorkEventArgs^ e) {
//... logic
UpdateTxtOutput("Some message");
//... more logic
}
I have a RitchTextBox called txtOutput, also the windows form control containing this code is called frmMain, the UpdateTxtOutput is defined in three parts as follows:
delegate void UpdateTxtOutputDelegate(String^ text);
void UpdateTxtOutput(String^ text)
{
UpdateTxtOutputDelegate^ action = gcnew UpdateTxtOutputDelegate(this, &frmMain::Worker);
this->BeginInvoke(action, text);
}
void Worker(String^ text)
{
txtOutput->AppendText("\t" + text + "\n");
}
I managed to get it working by simplifying the method within the 'MainForm' class to:
void EagleEye_Server::MainForm::postDebugMessage(String^ message)
{
Monitor::Enter(DebugTextBox);
DebugTextBox->AppendText(message);
Monitor::Exit(DebugTextBox);
}
And then moving the 'Invoke' call to the method calling the delegate, not pretty but it works for now. I think the issue may have been caused by the form getting stuck inside an Invoke loop. I say this as I noticed that the form would lock up and stop responding after it hit the recursive Invoke statement.
Sorry for my poor English :(
I use a class named SerialPort inherited from QObject:
serial_port.cpp & serial_port.h:
class SerialPort: public QObject{
Q_OBJECT
private:
bool checkStatusConnected();
private slots:
void readData();
}
bool SerialPort::checkStatusConnected(){
port.waitForReadyRead(200);
QBytesArray recv = port.readAll();
QString tmp = (QString)recv;
if(tmp.contains("Connected", Qt::CaseInsensitive))
return true;
return false;
}
MainWindow.cpp
void MainWindow::on_btnConn_clicked()
{
QThread* thread = new QThread(this);
serialport->moveToThread(thread);
serialport->connect();
}
In SerialPort::connect() I opened the port and send the connect command. Till now everything is ok. Due to slow speed of serial port I need to check the string return to me before next actions, so in SerialPort::connect() I call checkStatusConnected(). However, in this function waitForReadyRead() freezes the GUI thread as long as the time I set which makes me confused.
Why is the GUI thread blocked by another QThread and how to solve this problem?
Thanks!
You don't need to use threads for that. QSerialPort is event driven and works asynchronously. Use a timer to see whether you have received something within the required time.
QSerialPort port(....);
connect(&port, SIGNAL(readyRead()), this, SLOT(readFromSerialPort()));
QTimer timer;
timer.setInterVal(1000); // time you want to wait
connect(&timer, SIGNAL(timeout()), this, SLOT(handleTimeout()));
void SomeClass::readFromSerialPort()
{
QByteArray data(port.readAll());
// do somework
}
Found the examples. Check this out, this will suffice your needs I think.
http://doc.qt.io/qt-5/qtserialport-creaderasync-example.html
I created an application in which I would like to add a loading screen when the application is opening a project because the loading of the project can be long and sometimes, the gui blocks so the user can think there is a crash.
So I tried with QThread, reading doc and "solved" examples on this forum but nothing to do, I can't make it work.
I have a MainWindow class which deals with GUI and this class is the one I create in the main function :
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
Then I have :
mainwindow.h
class MyThread;
class MainWindow : public QMainWindow
{
Q_OBJECT
...
private :
Controller *controller;//inherits from QObject and loads the project
QList<MyThread*> threads;
public slots :
void animateLoadingScreen(int inValue);
}
mainwindow.cpp
MainWindow::MainWindow(...)
{
controller=new Controller(...);
threads.append(new MyThread(30, this));
connect(threads[0], SIGNAL(valueChanged(int)), this, SLOT(animateLoadingScreen(int)));
}
void MainWindow::animateLoadingScreen(int inValue)
{
cout<<"MainWindow::animateLoadingScreen"<<endl;
widgetLoadingScreen->updateValue(inValue);//to update the animation
}
void MainWindow::openProject()
{
widgetLoadingScreen->show()://a widget containing a spinner for example
threads[0]->start();//I want to launch the other thread here
controller->openProject();
threads[0]->exit(0);//end of thread so end of loading screen
}
MyThread.h
class MyThread : public QThread
{
Q_OBJECT;
public:
explicit MyThread(int interval, QObject* parent = 0);
~MyThread();
signals:
void valueChanged(int);
private slots:
void count(void);
protected:
void run(void);
private:
int i;
int inc;
int intvl;
QTimer* timer;
};
MyThread.cpp
MyThread::MyThread(int interval, QObject* parent): QThread(parent), i(0), inc(-1), intvl(interval), timer(0)
{
}
void MyThread::run(void)
{
if(timer == 0)
{
timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(count()));
}
timer->start(intvl);
exec();
}
void MyThread::count(void)
{
if(i >= 100 || i <= 0)
inc = -inc;
i += inc;
emit valueChanged(i);
}
When I execute the app, and click on open button which launches MainWindow::openProject(), I get :
QObject: Cannot create children for a parent that is in a different thread.
(Parent is MyThread(0x5463930), parent's thread is QThread(0x3cd1f80), current thread is MyThread(0x5463930)
MainWindow::animateLoadingScreen
MainWindow::animateLoadingScreen
....
MainWindow::animateLoadingScreen
MainWindow::animateLoadingScreen
(and here the controller outputs. and no MainWindow::animateLoadingScreen anymore so the widget loading screen is never animated during the opening of the project)
So what do I have to do, what do I have to put in MyThread class, how to link its signal to MainWindow to update the loading screen. And I think that there may be a problem with widgetLoadingScreen which is created in MainWindow so if MainWindow is blocked beacause of the opening, the widgetLoadingScreen can't be updated since it is in the thread of MainWindow which handles the GUI ?!
I read :
http://www.qtcentre.org/wiki/index.php?title=Updating_GUI_from_QThread
but with that one, I got error message at runtime, it's the one I use in the code I give above
QObject: Cannot create children for a parent that is in a different thread.
(Parent is MyThread(0x41938e0), parent's thread is QThread(0x1221f80), current thread is MyThread(0x41938e0)
I tried that too :
How to emit cross-thread signal in Qt?
but, even if I don't have the error message at runtime, it's the same for the animation which is not updated.
I am completely lost, and I don't think it's something difficult to do to have a loading screen in a thread while the main thread is opening a project?!
Qt has a QSplashScreen class which you could use for a loading screen.
Besides this, one of the problems you have is due to thread affinity (the thread in which an object is running) and the fact that you've decided to inherit from QThread.
In my opinion, QThread has a misleading name. It's more of a thread controller and unless you want to change how Qt handles threads, you really shouldn't inherit from it and many will tell you that "You're doing it Wrong!"
By inheriting QThread, your instance of MyThread is running on the main thread. However, when a call to exec() is made, it starts the event loop for the new thread and all its children, which includes the QTimer, and tries to move it to the new thread.
The correct way to solve this is not to inherit from QThread, but to create a worker object, derived from QObject and move it to the new thread. You can read about how to 'Really Truly Use QThread' here.
1st problem - runtime error with QTimer
Problem is in void MyThread::run(void), line timer = new QTimer(this);. The thread instance is created in (and so owned by) different (main) thread then it represents. For this reason, you cannot use thread as parent for object created inside the thread. In your case, solution is simple - create the timer on stack.
Example:
void MyThread::run(void)
{
QTimer timer;
connect(&timer, SIGNAL(timeout()), this, SLOT(count()));
timer.start(intvl);
// Following method start event loop which makes sure that timer
// will exists. When this method ends, timer will be automatically
// destroyed and thread ends.
exec();
}
2nd problem - GUI not updating
Qt requires the GUI to be created and displayed from main application thread. This means that blocking main thread with big operation blocks whole GUI. There are only 2 possible solutions:
Move the heavy work to other (loading) thread. This is best solution and I believe it's worth the effort (I'm aware you wrote that this would be problematic).
During the heavy operation, call regularly QCoreApplication::processEvents() - each time you call this, events will be processed, which includes calling slots, key and mouse events, GUI redraw etc. The more often you call this, the more responsive GUI will be. This is simpler to implement (just put one line all over the code), but it's quite ugly and if the operation blocks on loading a file, the GUI will freeze for some time. That means that responsiveness of your GUI depends on interval between calls. (But if you call it too often, you will slow down the loading progress.) This technique is discouraged and it's best to avoid it...
The way I will do it based on the default example on Qthread Page:
Break the big controller->openProject(); such that it updates a variable
provide access to that variable using a signal ( like statusChanged(int)).
Do what you need to do once the signal is triggered.
The code looks like
class Worker : public QObject
{
Q_OBJECT
QThread workerThread;
private:
int status; //
bool hasworktoDo();
void doSmallWork();
public slots:
void doWork() {
while(hasworktoDo())
{
doSmallWork(); // fragments of controller->openProject();
++status; //previously set to 0
emit statusChanged(status);
}
emit resultReady(result);
}
signals:
void resultReady(const QString &result);
void statusChanged(int value);
};
class Controller : public QObject
{
Q_OBJECT
QThread workerThread;
public:
Controller() {
Worker *worker = new Worker;
worker->moveToThread(&workerThread);
connect(workerThread, SIGNAL(statusChanged(int)), this, SLOT(updateStatus(int)));
connect(workerThread, SIGNAL(finished()), worker, SLOT(deleteLater()));
connect(this, SIGNAL(operate()), worker, SLOT(doWork()));
connect(worker, SIGNAL(resultReady(QString)), this, SLOT(handleResults(QString)));
workerThread.start();
}
~Controller() {
workerThread.quit();
workerThread.wait();
}
public slots:
void handleResults(const QString &);
void updateStatus(int value)
{
int status = value;
//now you have what to use to update the ui
}
signals:
void operate(); //
};
If you have trouble breaking the openProject operations in small parts, it just mean it is pointless to say on the UI that you are at 50%... Just say Loading... and make the code simpler. Note that you don't need a timer in my case, as the worker sends regular updates