text append waits until hcitoo scan is finished

Jamieghosal

I am also facing some kind of erroneous things which I am sharing along with btconnect.h file -
This is my btconnect.h file

#ifndef BTCONNECT_H
#define BTCONNECT_H

#include "scandialog.h"

namespace Ui {
class BTConnect;
}

class BTConnect : public QWidget
{
Q_OBJECT

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

private slots:
void on_ScanButton_clicked();

void ScanBTDevices();

//some slots here

void ScanDialogShow();

void ScanDialogClose();

public slots:
//some slots here

private:
Ui::BTConnect *ui;

QProcess BTscan_Process;

scanDialog *scan;

};

#endif // BTCONNECT_H
btconnect.cpp

BTConnect::BTConnect(QWidget *parent) :
QWidget(parent),
ui(new Ui::BTConnect)
{
//set the userinterface as BTConnect.ui
ui->setupUi(this);

scan = new scanDialog(this);

}

void BTConnect::ScanDialogShow()
{
scan->show();
}

void BTConnect::ScanDialogClose()
{
scan->close();
}

void BTConnect::ScanBTDevices()
{
ScanDialogShow();

//Command to scan nearby bluetooth devices
//"hcitool scan"
QString cmd("hcitool scan");

//start the process
BTscan_Process.start(cmd);

//Wait for the processs to finish with a timeout of 20 seconds
if(BTscan_Process.waitForFinished(20000))
{
    //Clear the list widget
    this->ui->listWidget->clear();

    //Read the command line output and store it in QString out
    QString out(BTscan_Process.readAllStandardOutput());

    //Split the QString every new line and save theve in a QStringList
    QStringList OutSplit = out.split("\n");

    //Parse the QStringList in btCellsParser
    btCellsParser cp(OutSplit);

    for(unsigned int i = 0; i<cp.count(); i++)
    {
       //writing in listwidget
    }

}

ScanDialogClose();

}

void BTConnect::on_ScanButton_clicked()
{
//Scan for available nearby bluetooth devices
ScanBTDevices();
}
if I use the above code, the qdialog scandialog does open when the process begins and closes when the data is loaded in qlistwidget, but the contents of qdialog scandialog are not displayed. If I were to change show() to exec(), the contents will be shown but the QProcess does not run until the dialog is closed.

I want the dialog to open when the Qprocess starts and close when the qlistwidget is loaded with data from the scan. And I want the contents of scandialog to be displayed. It has two labels. One with .GIF file and another with text saying scanning.

Any help is appreciated.

Answer - 1
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The problem is that QDialog::exec and QProcess::waitForFinished functions block event loop. Never ever block event loop. So you just need to do things more asynchronously.

QProcess class can be handled asynchronously using signals like readReadStandardOutput. And QDialog can be shown asynchronously using open slot.

The example:

void ScanBTDevices() {
// Open dialog when process is started
connect(process, SIGNAL(started()), dialog, SLOT(open()));

// Read standard output asynchronously
connect(process, SIGNAL(readyReadStandardOutput()), SLOT(onReadyRead()));

// Start process asynchronously (for example I use recursive ls)
process->start("ls -R /");

}

void onReadyRead() {
// Write to list widget
dialog->appendText(QString(process->readAllStandardOutput()));
}
The data will be appended to the dialog during generating by process. Also using QProcess::finished signal and you can close the dialog.

by *
Answer - 2 verified
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you never return to the event loop when you do show (because of waitForFinished) and you never continue to the processing code when you do exec

instead of the waitForFinished you should connect to the finished signal and handle it there and use a single shot timer that will cancel it:

void BTConnect::on_BTscanFinished()//new slot
{
//Clear the list widget
this->ui->listWidget->clear();

//Read the command line output and store it in QString out
QString out(BTscan_Process.readAllStandardOutput());

After doing all of this I basically stuck on virtual onboarding software.
//Split the QString every new line and save theve in a QStringList
QStringList OutSplit = out.split("\n");

//Parse the QStringList in btCellsParser
btCellsParser cp(OutSplit);

for(unsigned int i = 0; i<cp.count(); i++)
{
   //writing in listwidget
}
ScanDialogClose();

}

void BTConnect::ScanBTDevices()
{
ScanDialogShow();

//Command to scan nearby bluetooth devices
//"hcitool scan"
QString cmd("hcitool scan");

//start the process
connect(BTscan_Process, SIGNAL(finished()), this, SLOT(on_BTscanFinished()));
BTscan_Process.start(cmd);
QTimer::singleShot(20000, scan, SLOT(close()));

}

Hope this will properly help you.

Anonymous_Banned275

@Jamieghosal Many thanks for the post. I am glad I found somebody who does "Bluetooth" coding.
Your post is a big help, however at this time I have to fix "updating" QT.
The example function is OK , but it still keep QT from updating until it is finished. I need to work on that first.

Speaking of Bluetooth - I am very often experiencing a total "screw-up" - even using commands running terminal won't work. The only "solution" is to switch / reboot to another OS _ I am, running multi-boot - all Ubuntu.

I really believe "bluez" is the worst application and it is "part of the Linux kernel" - hence I am trying to bypass it using HCI directly.

Anonymous_Banned275

@ChrisW67 Yes, QTBluetooth "support" won't even recognize that I turned Bluetooth off in OS - and happily reports "finished " - no error.
I did try at lest two versions of QTCreator with same result.
FYI _ I am using Ubuntu.

Anonymous_Banned275

@Jamieghosal I think the basic "problem" is

OProcess.waitForFinished(60000);

I do not get how QT executes basic C function by "waiting" for it to return "true".
That basically blocks the rest of the code and I expect "process" not to do that.
So it back to finding out how to make "process" NOT to block the rest of the code. Long time ago I used QProgressBar and it is the time to try it again - I should be able to "update" the QProgressBar on each second - hence the QProcess needs to be convinced to do so.

SGaist

@AnneRanch QProcess is asynchronous as already explained. Learn how to use it that way.

Anonymous_Banned275

@SGaist And what do you think I am doing ? I do not need such comments.
Cheers

SGaist

Well, you are using the blocking API, hence my suggestion. Stop doing that and use signals and slots to manage your QProcess object.

Make a list of the commands you want to execute. Pick the first, start it, then when it is done (use the finished signal to know), start the next on the list and so on until they are all done. No freeze will happen.

Anonymous_Banned275

@SGaist Tep, that is what I am doing and as usual I am stuck on "connect".
Sure could use a real example of connect to get me going...
This "wait for completion" sure was of no help to really understand QProcess...

SGaist

There's an example in the finished signal documentation using a lambda.
There's a chapter dedicated to the explanation on how signal and slots work.

J.Hilk

@AnneRanch said in text append waits until hcitoo scan is finished:

Tep, that is what I am doing and as usual I am stuck on "connect".
Sure could use a real example of connect to get me going...
This "wait for completion" sure was of no help to really understand QProcess...

does this help?

#ifndef HCITOOLPROCESS_H
#define HCITOOLPROCESS_H

#include <QObject>
#include <QProcess>
#include <QElapsedTimer>
#include <iostream>

class HciToolProcess : public QObject
{
    Q_OBJECT
public:
    enum HciCommands : uint8_t {
        Dev,
        Inq,
        Scan,
    };

    explicit HciToolProcess(QObject *parent = nullptr) : QObject(parent), m_currentCommand{HciCommands::Dev}
    {
        connect(&m_process, QOverload<int,QProcess::ExitStatus>::of(&QProcess::finished), this, &HciToolProcess::nextCommand);
    }

    bool startProcess(){
        if(m_currentCommand != HciCommands::Dev)
            return false;

        m_elapsedTime.start();

        m_process.start(QStringLiteral("hcitool"), QStringList(HciCommandToString(m_currentCommand)), QIODevice::ReadWrite);

        return true;
    }

signals:
    void timeElapsed(const QString &time); // to update your textEdit_2
    void allProcessesDone();

private:
    void nextCommand(int exitCode, QProcess::ExitStatus exitStatus){
        std::cout<<"\n * Program to demonstrate the usage of linux commands in qt * \n";

        QString StdOut      =   m_process.readAllStandardOutput();  //Reads standard output
        QString StdError    =   m_process.readAllStandardError();   //Reads standard error

        std::cout<<"\n Printing the standard output..........\n";
        std::cout<<std::endl<<StdOut.toStdString();
        std::cout<<"\n Printing the standard error..........\n";
        std::cout<<std::endl<<StdError.toStdString();
        std::cout<<"\n Printing exit code..........\n";
        std::cout<<std::endl<<exitCode;
        std::cout<<"\n Printing exitStatus..........\n";
        std::cout<<std::endl<<exitStatus;
        std::cout<<"\n\n";

        QString elapsedTime = QString::number(m_elapsedTime.restart());
        emit timeElapsed(elapsedTime);

        m_currentCommand = static_cast<HciCommands>(m_currentCommand + 1);
        if(static_cast<uint8_t>(m_currentCommand) <= static_cast<uint8_t>(HciCommands::Scan)){
            m_process.start(QStringLiteral("hcitool"), QStringList(HciCommandToString(m_currentCommand)), QIODevice::ReadWrite);
        } else {
            m_currentCommand = HciCommands::Dev;
            emit allProcessesDone();
        }
    }

    QString HciCommandToString( HciCommands cmd) {
        switch (cmd) {
        case HciCommands::Dev: return QStringLiteral("dev");
        case HciCommands::Inq: return QStringLiteral("inq");
        case HciCommands::Scan: return QStringLiteral("scan");
        default:
            Q_UNREACHABLE();
            return QLatin1String();
        }
    }

private:
    QElapsedTimer m_elapsedTime;
    HciCommands m_currentCommand;
    QProcess m_process;
};

#endif // HCITOOLPROCESS_H

JonB

@J-Hilk
I was thinking about writing something like this, but assumed the effort would be ignored.

If you were to get rid of your enumeration/switch statement and instead create some list of the commands (plus parameters) to be used, which the caller passes/sets on the class, it would be a generic "execute any arbitrary list of commands sequentially" class.

J.Hilk

@JonB sure, here ya go :D

#ifndef HCITOOLPROCESS_H
#define HCITOOLPROCESS_H

#include <QObject>
#include <QProcess>
#include <QElapsedTimer>
#include <iostream>

class HciToolProcess : public QObject
{
    Q_OBJECT
public:

    struct CommandAndArguments{
        QString command;
        QStringList arguments;
    };

    explicit HciToolProcess(QObject *parent = nullptr) : QObject(parent), m_index{-1}
    {
        connect(&m_process, QOverload<int,QProcess::ExitStatus>::of(&QProcess::finished), this, &HciToolProcess::onProcessFinished);
    }

    bool startProcess(QList<CommandAndArguments> commands){
        if(m_index != -1 || commands.isEmpty())
            return false;

        m_cmdAndArgs = commands;

        m_elapsedTime.start();

        //m_index is -1 so the function will set it to 0
        processCommandAndArguments();

        return true;
    }

signals:
    void timeElapsed(const QString &time); // to update your textEdit_2
    void allProcessesDone();

private:
    void processCommandAndArguments(){
        m_index++;
        if(m_index < m_cmdAndArgs.size()){
            m_process.start(m_cmdAndArgs.at(m_index).command, m_cmdAndArgs.at(m_index).arguments, QIODevice::ReadWrite);
        } else {
            m_index = -1;
            emit allProcessesDone();
        }
    }

    void onProcessFinished(int exitCode, QProcess::ExitStatus exitStatus){
        std::cout<<"\n * Program to demonstrate the usage of linux commands in qt * \n";

        QString StdOut      =   m_process.readAllStandardOutput();  //Reads standard output
        QString StdError    =   m_process.readAllStandardError();   //Reads standard error

        std::cout<<"\n Printing the standard output..........\n";
        std::cout<<std::endl<<StdOut.toStdString();
        std::cout<<"\n Printing the standard error..........\n";
        std::cout<<std::endl<<StdError.toStdString();
        std::cout<<"\n Printing exit code..........\n";
        std::cout<<std::endl<<exitCode;
        std::cout<<"\n Printing exitStatus..........\n";
        std::cout<<std::endl<<exitStatus;
        std::cout<<"\n\n";

        QString elapsedTime = QString::number(m_elapsedTime.restart());
        emit timeElapsed(elapsedTime);

        processCommandAndArguments();
    }

private:
    QElapsedTimer m_elapsedTime;
    QProcess m_process;
    QList<CommandAndArguments> m_cmdAndArgs;
    int32_t m_index;
};

#endif // HCITOOLPROCESS_H