text append waits until hcitoo scan is finished

ChrisW67

The UI is not updated until the program returns to the Qt event loop; which is after this function exits.

You could output timestamps into your text edit before/after each call. They'll all appear when the function exits.
You could use the time Linux/UNIX command to time hcitool outside of the Qt program (and capture that output).
You could use the Qt provided Bluetooth functionality instead.

SGaist

Hi,

If you really want asynchronous handling, use QProcess rather than system.

JonB

@AnneRanch
In addition to @ChrisW67's [and Now @SGaist too] excellent points, if you really want to write your code this way (it's not the Qt way) you could try putting qApp->processEvents() after each append() line, I think that will show your updates in the UI.

J.Hilk

@JonB don't hand out guns for people to shoot themselves with. It's easy enough in c++ 😜

Anonymous_Banned275

@ChrisW67As always, you are correct.
So I found this example and it is sort of working.
When I first run it I got "file not found" error - which was expected.
(I think if I run this function only once , in push button event , I wdillw get the file erro back
Now I have two problems - still getting the error BUT no longer includes the "file is missing message" . Then the hcitoll won't terminate and that gives another error.

Printing the standard error..........

QProcess: Destroyed while process ("hcitool") is still running.
Form::ProcessCommand(QString command )

. So I am not sure why hcotool won't terminate, but I think it is the dunction which won't finish the error message.
Because it works just fine , without getting the full error when call the to function single.
I really do not need to call all the commands in sequence as I am testin in now.

So I'll work on the error.

BTW
How do I pass an empty "argument list ?
.

timer.start();

// ProcessCommand("hcitool", {" "}); no arg list - does not work
// ProcessCommand("hcitool",{ " "});
ProcessCommand("hcitool",{ "dev"});
ProcessCommand("hcitool", {"inq"});
ProcessCommand("hcitool", {"scan "});

Here is the current , UNDER CONSTRUCTION, version of the usage of QProcess

int Form::ProcessCommand(QString Command, QStringList args  )
{
    qDebug("Form::ProcessCommand(QString command ) ");
    std::cout<<"\n * Program to demonstrate the usage of linux commands in qt * \n";
    timer.elapsed();
    QString s = QString::number(timer.elapsed());
    s = "ProcessCommand START  elapsed time " + s;
    ui->textEdit_2->append(s);
    QProcess OProcess;
    //    QString Command;    //Contains the command to be executed
    //    QStringList args;   //Contains arguments of the command
    //    Command = "ls";
    //    args<<"-l"<<"/home/anil";

    OProcess.start(Command,args,QIODevice::ReadWrite); //Starts execution of command
    //QProcess.start(Command,)
    OProcess.waitForFinished();                       //Waits for execution to complete

    QString StdOut      =   OProcess.readAllStandardOutput();  //Reads standard output
    QString StdError    =   OProcess.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\n";
    s = QString::number(timer.elapsed());
        s = "ProcessCommand END elapsed time " + s;
        ui->textEdit_2->append(s);



            //system(Command.toStdString().c_str());  //>> log_file.txt);
            return 0;
};

SGaist

Using QProcess that way is more or less the same as calling system since you are blocking the event loop.

Anonymous_Banned275

My last post is little screwed-up.
The error text is always executed and reason I do no have a real error - I did not add the "redirect " to file yet.

Which is subject of this post

what exactly is QIODevice as coded in an example ?
QIODevice::Append append to file - so where in the "start" I add the file ?
This adds file data to arg . Is that correct ?
//Process.Start("cmd.exe", "/c foo.exe -arg >" + dumpDir + "\foo_arg.txt");
How can I option to execute BOTH
QIODevice::ReadWrite & QIODevice::Append)
this did not work

Anonymous_Banned275

@SGaist Good point, but it does not matter in my application. I am more concerned why I cannot run the function consecutively.
Cheers

SGaist

it's the base class of QProcess
No it's not, at best it will overwrite the file. If you want to append to a file in a shell you need to use >>
You want to execute your process, then read the output it generated though QProcess API and then use a QFile to write what you want to the file. QProcess is not a full shell so the redirection that you try to use won't work.

Anonymous_Banned275

@SGaist It works as expected when I add the file redirection in "arg".
I am back to need refresh course on "HCI".
My process function is timing out because there is no response from "hcitool".
I am really frustrated with this Bluetooth stuff - how low do I have to go to get it working / responding reliably and in time. I believe there is a spec somewhere to tell how long before the HCI commands timeout.

I have no issue with local "dev" but it is the "scan" or "inq" which is killing the process .

ChrisW67

The blocking behaviour of hcitool is not a Qt problem. hcitool has options for controlling timeouts (at least the Bluez source code I am looking at does). However, you seem to be running something on Windows, so I have no idea what your hcittool really is.

Is there a reason that you are not using the Qt Bluetooth support?

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
0 arrow_circle_up 0 arrow_circle_down
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.