QFutureWatcher - timing issue

Anonymous_Banned275

OK, I admit I have a basic misunderstanding of the "connections" between parts of the code.
I need 10 second delay , I picked 10 iterations of 1 second time delay monitoring elapsed time instead of using magic numbers to eat CPU.
( if there is a better way to do that please make a suggestion how.)

I have NOT changed any of the "connect" functions.

The progress of the delay is displayed in modal

QProgressDialog dialog ( "TEST window title ",
" BUTTON text", 0, iterations ,0 ,0);

run as

dialog.exec();

The dialog shows progress of 10 % and then jumps to 50% and closes.

I monitor the entire time of the dialog.exec(); and it reads approximately 3 seconds.

Apparently I need to figure out HOW to actually read the futurewatcher SINGAL to find out WHY the values are not as expected AND where are they coming form.

I am not sure if I can read the values while running dialog.exec(); AKA how to access current values of interest.

I

Pablo J. Rogina

@AnneRanch said in QFutureWatcher - timing issue:

default constrictor

Are you coding in Python?

PS: sorry but I couldn't resist...

Anonymous_Banned275

@Pablo-J-Rogina said in QFutureWatcher - timing issue:

@AnneRanch said in QFutureWatcher - timing issue:

default constrictor

Are you coding in Python?

PS: sorry but I couldn't resist...

I am about to start coding in machine language...
This Qt stuff with its defaults / inheritance etc. is driving me nuts.

'BTW the "constrictor" I used does not do simple window title as advertised.
Wonder what other parameters passed to it do not work...

SGaist

Hi,

Please show the code you are currently using. That will help us better understand what happens to you.

Anonymous_Banned275

@SGaist said in QFutureWatcher - timing issue:

Hi,

Please show the code you are currently using. That will help us better understand what happens to you.

Are you positive ?
My code is currently more debug lines than code and from past experience I am reluctant to post it . I do not need my coding style criticized by Peanut gallery .

In the mean time
I think my issue is in interaction of QProgressDialog changing "the value" , and actually understanding` what is the value. I though it is the percentage of completion of the QProgressDialog "progress bar" related to # of iterations, but I may be wrong.

   QObject::connect(&futureWatcher, SIGNAL(progressRangeChanged(int,int)), &dialog, SLOT(setRange(int,int)));
    QObject::connect(&futureWatcher, SIGNAL(progressValueChanged(int)), &dialog, SLOT(setValue(int)));

    // Start the computation.
    qDebug()<<" Start the computation - ";
    qDebug()<< "apply delay function "spin"  to each vector";

    futureWatcher.setFuture(QtConcurrent::map(vector, spin));

 //  futureWatcher.setFuture();

    // Display the dialog and start the event loop.
    qDebug()<<" RUN dialog.exec() Display the dialog and start the dialog event loop";

    //   dialog.setMaximum(50);
    // dialog.setRange(10, 50 );

    qDebug()<<" START dialog.exec() " ; // ? << dialog.setRange(10,30);
    // progress dialog event loop
    //dialog.setAutoClose(false); // test do not close disklog when finished
    // show % of completion in progress bar
    // timing loop runs thru # of iterations
    // show / run modal dialog
    // NOTE perror is phoney

    // test real duration of dialog here
    QElapsedTimer timer_wait;
    timer_wait.start();
//     futureWatcher.progressValue()
    qDebug()<<"futureWatcher.progressValue() " << futureWatcher.progressValue();

attempt to monitor the actual "value" 

    dialog.exec(); // run modal dialog 

    qDebug()<<"futureWatcher.progressValue() " << futureWatcher.progressValue();

My attempt to monitor the actual "value" , at least at start and the end of the

dialog.exec(); // run modal dialog

Not sure why

the end is set at "10" - should be 100 , but how - default again ?
is it even possible to monitor modal dialog for changes?
perhaps adding my own slots to connect to QProgressDialog ?

SGaist

@AnneRanch said in QFutureWatcher - timing issue:

I do not need my coding style criticized by Peanut gallery .

I'd avoid getting rude.

@AnneRanch said in QFutureWatcher - timing issue:

the end is set at "10" - should be 100 , but how - default again ?

The dialog creation/initialisation is missing from your code snippet.

@AnneRanch said in QFutureWatcher - timing issue:

is it even possible to monitor modal dialog for changes?
perhaps adding my own slots to connect to QProgressDialog ?

What monitoring do you have in mind ?

Anonymous_Banned275

@SGaist said in QFutureWatcher - timing issue:

@AnneRanch said in QFutureWatcher - timing issue:

I do not need my coding style criticized by Peanut gallery .

I'd avoid getting rude.

@AnneRanch said in QFutureWatcher - timing issue:

the end is set at "10" - should be 100 , but how - default again ?

The dialog creation/initialisation is missing from your code snippet.

@AnneRanch said in QFutureWatcher - timing issue:

is it even possible to monitor modal dialog for changes?
perhaps adding my own slots to connect to QProgressDialog ?

What monitoring do you have in mind ?

As fae as I can tell the QProgressDialog can only follow what QFutureWatcher SIGNALS value and range is being set.
Since I opeted to use QProgressDialog dialog,exec() I really have no tracking means to see these.
Of course I could replace the dialog,exec() with code from documents.

OK, here is my current code - lock , stock and barrel...

#include "configuredialog.h"
#include "ui_configuredialog.h"
#include "project_commonheader.h"


ConfigureDialog::ConfigureDialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::ConfigureDialog)
{
    ui->setupUi(this);
}

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

// #of iteration ?? netartion is actaully
// % step
// when in 20 it takes steps in 20 %  of total
// this emulates the time consuming function
void spin(int& iteration)
{
#ifdef PROCESS
#ifdef TRACE
    // qDebug() << "QDEBUG TRACE ";
    qDebug () << " delay spin pass #" << iteration ;
    qDebug() << "QDEBUG TRACE TASK \n\t\t emulate the time consuming function \n";
    //qDebug() << "QDEBUG TRACE TASK \n\t\t find nearby BT devices \n";
#ifdef BYPASS
    qDebug() << "file     " << __FILE__;
    qDebug() << "function "<<__FUNCTION__;
    qDebug() << "@line    " << __LINE__;
    qDebug()<<"TEMPORARY EXIT ";
    //exit(99);
#endif
#endif
#endif
    
    int static access;
    if(!access )
    {
#ifdef PROCESS
        qDebug() << "RUN  START long process ....";
#endif
        access++;
    }
#ifdef PROCESS
    qDebug() << "RUN  CONTINUE long process ....";
    
    // actuall steps MN
    // adding elapsed timer
    //    int  Time_Step  = ui->spinBoxIterations_2->text().toInt();
#endif
    
    QElapsedTimer timer;
    timer.start();
    //slowOperation();  // we want to measure the time of this slowOperation()
    // qDebug() << timer.elapsed();
    //#ifdef BYPASS
    do
    {
        //qDebug() << " do / while timer.elapsed()";
        ;
    }while(timer.elapsed() <= 1000); // MN  1 second Time_Step);
    //#endif
    
#ifdef BYPASS
    const int work = 10000 * 1000 * 33;      // increased by 1000
    volatile int v = 0;
    // the time emulator
    for (int j = 0; j < work; ++j)
        ++v;                                       // step delay loop MN
#endif
    qDebug() << "Estimated single iteration delay elapsed time " << timer.elapsed()<< " mS";
    
#ifdef PROCESS
    qDebug() << "iteration" << iteration << "in thread" << QThread::currentThreadId();
    //slowOperation();  // we want to measure the time of this slowOperation()
    qDebug() << "Estimated single iteration delkay elapsed time " << timer.elapsed()<< " mS";
#endif
    
    qDebug() << "iteration # " << iteration << "in thread" << QThread::currentThreadId();
    
    
    
    
    
}

#ifdef BYPASS
What defaults? The connection, I've shown above and which is used in your example,
sets up the QProgressDialog according to your QFutureWatchers "watched" work.

progressRangeChanged(int,int) will set the range (0% - 100%) to (0, 10), where 10 = 100%. So each iteration (total of 10) equals 10%.
        Every time one iteration is done (one iteration = count from 0 to 1000*1000*40), progressValueChanged(int) is emitted and sets the corresponding percentage in your QProgressDialog.
Then, in the end, waitForFinished() is called to "block" the main thread until all future work has been done (and to ensure that you have all results from all threads, when reaching this point in your code).

Probably your QElapsedTimer causes the issue, because it traps your thread in your do - while loop.

#endif
// initialize time consuming task
void ConfigureDialog::on_doTaskButton_clicked()
{
    
    
# ifdef TRACE
    qDebug() << "QDEBUG TRACE START void TaskDialog::on_doTaskButton_clicked()";
    qDebug() << "file     " << __FILE__;
    qDebug() << "function "<<__FUNCTION__;
    qDebug() << "@line    " << __LINE__;
    //qDebug()<<"TEMPORARY EXIT ";
    //   return;#ifdef BYPASS
#endif
    // start run overall timer
    QElapsedTimer timer;
    timer.start();
    
    // Prepare the vector.
    // what does it really do ?
    
    int iterations = ui->spinBoxIterations->text().toInt();
    // how may iotera5tions to display 100% competion ??
    // temporary MN
    iterations = 10;
    
    qDebug()  << " Setup # of iterations = toatal delay " << iterations  << " seconds";
    
#ifdef PROCESS
    qDebug()<<" # of iterations ?? " << iterations ; // vector.append(i) LOOP ";
    // return;
    qDebug() << "Estimated elapsed time " << timer.elapsed()<< " mS";
    // dynamic array # one for each iteration
    // how often to update progress dialog
#endif
    qDebug()  << " Setup # of iterations as vector array ";
    QVector<int> vector;
    for (int i = 0; i < iterations; ++i)
    {
#ifdef PROCESS
        //qDebug()<<" interations loop ?? index " << i;
        qDebug()<<" vector.append(i) index " << i; // LOOP ";
        // another delay "iterations
        //qDebug()<<" another delay iterations (?) ";
#endif
        vector.append(i);
    }
    
    
#ifdef BYPASS
    QLabel *label = new QLabel;
    QScrollBar *scrollBar = new QScrollBar;
    QObject::connect(scrollBar, SIGNAL(valueChanged(int)),
                     label,  SLOT(setNum(int)));
#endif
    
    
    // return;
    // Create a progress dialog. implements iteration
    // shows progress ion %
    // BUG doe not finish 100%
    
    qDebug()<<" Setup Create a QProgressDialog dialog - set paramaters ";
    // this is a default QProgressDialog constructor
    //QProgressDialog dialog;
    //    	QProgressDialog(const QString & labelText,
    //    const QString & cancelButtonText, int minimum, int maximum,
    //            QWidget * parent = 0, Qt::WindowFlags f = 0)
    QProgressDialog dialog ( "TEST window title   ",
                             " BUTTON text", 0, iterations ,0 ,0);
    //BUG  did not set to TEST window title  here
    // dialog.setWindowModality(Qt::WindowModal);
    
    //     dialog.labelText(" what is label ?" ); no matching function ??
    dialog.setWindowTitle("TEST window title  ");
    
    dialog.setFixedWidth(500);                    //W.setWindowTitle("TEST window title  ");
    
    // set defaulrs  of what ???
    //    dialog.setMaximum(100);
    //    dialog.setRange(10, 1000 );
    
    //    If set to 0, the dialog is always shown as soon as any progress is set.
    //    The default is 4000 milliseconds.
    //    int	minimumDuration() const
    //    void	setMinimumDuration(int ms)
    
    dialog.setMinimumDuration(0);
    
    // single shot label only
    //This is done querying the number of processor cores
    dialog.setLabelText(QString("Progressing using %1 thread(s)...\nTODO Elapsed time %2  [mS] ")
                        .arg(QThread::idealThreadCount()).arg(timer.elapsed()));
    
    // Create a QFutureWatcher and connect signals and slots.
    qDebug()<<" Setup Create a QFutureWatcher";
    QFutureWatcher<void> futureWatcher;
    
    qDebug()<<" setup futureWatcher and dialog connect SIGNAL  SLOT ";
    // # of iterations ?? " << iterations ; // vector.append(i) LOOP ";
    
    qDebug()<<" setup future WatcherSIGNAL(finished()";
    // Resets the progress dialog. The progress dialog becomes hidden if autoClose() is true.
    //QObject::connect(&futureWatcher, SIGNAL(finished()), &dialog, SLOT(reset())); // reset to what ??
    
    
    qDebug()<<" setup dialog, SIGNAL(canceled()";
    //QObject::connect(&dialog, SIGNAL(canceled()), &futureWatcher, SLOT(cancel())); // TOK
    
    // how to emulate these ??
    QObject::connect(&futureWatcher, SIGNAL(progressRangeChanged(int,int)), &dialog, SLOT(setRange(int,int)));
    QObject::connect(&futureWatcher, SIGNAL(progressValueChanged(int)), &dialog, SLOT(setValue(int)));
    
    // Start the computation.
    qDebug()<<" Start the computation - ";
    qDebug()<< "apply delay function spin to each vector";
    
    futureWatcher.setFuture(QtConcurrent::map(vector, spin));
    
    //  futureWatcher.setFuture();
    
    // Display the dialog and start the event loop.
    qDebug()<<" RUN dialog.exec() Display the dialog and start the dialog event loop";
    
    //   dialog.setMaximum(50);
    // dialog.setRange(10, 50 );
    
    qDebug()<<" START dialog.exec() " ; // ? << dialog.setRange(10,30);
    // progress dialog event loop
    //dialog.setAutoClose(false); // test do not close disklog when finished
    // show % of completion in progress bar
    // timing loop runs thru # of iterations
    // show / run modal dialog
    // NOTE perror is phoney
    
    // test real duration of dialog here
    QElapsedTimer timer_wait;
    timer_wait.start();
    //     futureWatcher.progressValue()
    qDebug()<<"futureWatcher.progressValue() " << futureWatcher.progressValue();
    
    dialog.exec(); // run modal dialog 
    
    qDebug()<<"futureWatcher.progressValue() " << futureWatcher.progressValue();
    
    
    //qDebug()<<" START Display current range " ; // ? << dialog.setRange(10,30);
#ifdef BYPASS
    if( dialog.exec())
        \
    {
        perror("Accepted = 1 - sucess ");
    }
    else
    {
        perror("??  Accepted  != 1  say what ?? ");
    }
    ; // timing loop runs thru # of iterations
#endif
    qDebug()<<" END dialog.exec() "<< timer_wait.elapsed()<< " mS";
    //   qDebug() << "test real duration of dialog here " << timer_wait.elapsed()<< " mS";
    
    return;
    
    qDebug() << "Completed END FULL Estimated elapsed time " << timer.elapsed()<< " mS";
    
    // show last iteration result %
    qDebug()<<"last iteration resul t %  "<< iterations;
    qDebug()<<" END  Display current range ?? " ; // ? << dialog.setRange(10,30);
    // qDebug()<<" futureWatcher.waitForFinished()";
    // when setAUtoCLose is true   defualkt no need to wait for finshed ??
    // test wait time if any
    
    // this makes no snese since connect(&futureWatcher, SIGNAL(finished())
    // runs &dialog, SLOT(reset())
    
#ifdef PROCESS
    QElapsedTimer timer_wait;
    timer_wait.start();
    futureWatcher.waitForFinished();
    qDebug() << "test wait futureWatcher.waitForFinished()  time if any " << timer_wait.elapsed()<< " mS";
    
    // Query the future to check if was canceled.
    qDebug() << "DONE   (was) Canceled?" << futureWatcher.future().isCanceled();
#endif
    
# ifdef TRACE
    qDebug() << "QDEBUG TRACE END void TaskDialog::on_doTaskButton_clicked()";
    qDebug() << "file     " << __FILE__;
    qDebug() << "function "<<__FUNCTION__;
    qDebug() << "@line    " << __LINE__;
    //qDebug()<<"TEMPORARY EXIT ";
    //   return;#ifdef BYPASS
#endif
    
}


#ifdef BYPASS

	QFutureWatcher
#ifdef BYPASS

\temoprary bypaSS POROIGNAL
 
 
#include "taskdialog.h"
#include "ui_taskdialog.h"
#include <QtConcurrent>
#include <QProgressDialog>
#include <qtconcurrentmap.h>
 
 TaskDialog::TaskDialog(QWidget *parent) :
     QDialog(parent),
     ui(new Ui::TaskDialog)
 {
     ui->setupUi(this);
 }
 
 TaskDialog::~TaskDialog()
 {
     delete ui;
 }
 
 void spin(int& iteration)
 {
     const int work = 1000 * 1000 * 40;
     volatile int v = 0;
     for (int j = 0; j < work; ++j)
         ++v;
     
     qDebug() << "iteration" << iteration << "in thread" << QThread::currentThreadId();
 }
 
 void TaskDialog::on_doTaskButton_clicked()
 {
     
# ifdef TRACE
     qDebug() << "QDEBUG TRACE void TaskDialog::on_doTaskButton_clicked()";
     qDebug() << "file     " << __FILE__;
     qDebug() << "function "<<__FUNCTION__;
     qDebug() << "@line    " << __LINE__;
     qDebug()<<"TEMPORARY EXIT ";
     return;#ifdef BYPASS
        #endif
             
             
             // Prepare the vector.
             int iterations = ui->spinBoxIterations->text().toInt();
     QVector<int> vector;
     for (int i = 0; i < iterations; ++i)
         vector.append(i);
     
     // Create a progress dialog.
     // all defualts ?? no form ??
     
     QProgressDialog dialog;
     
     dialog.setLabelText(QString("Progressing using %1 thread(s)...").arg(QThread::idealThreadCount()));
     
     dialog.setLabelText(QString("Progressing using %1 thread(s)...").arg(QThread::idealThreadCount()));
     
     
     
     
     
     
     // Create a QFutureWatcher and connect signals and slots.
     QFutureWatcher<void> futureWatcher;
     QObject::connect(&futureWatcher, SIGNAL(finished()), &dialog, SLOT(reset()));
     QObject::connect(&dialog, SIGNAL(canceled()), &futureWatcher, SLOT(cancel()));
     QObject::connect(&futureWatcher, SIGNAL(progressRangeChanged(int,int)), &dialog, SLOT(setRange(int,int)));
     QObject::connect(&futureWatcher, SIGNAL(progressValueChanged(int)), &dialog, SLOT(setValue(int)));
     
     // Start the computation.
     // futureWatcher.setFuture(QtConcurrent::map(vector, spin));
     futureWatcher.setFuture(QtConcurrent::map(vector, spin));
     
     // Display the dialog and start the event loop.
     
     // this may be wrong
     
     
     
     
     
     
     
     
     
     
     
     dialog.exec();
     
     // this may be wrong
     
     
     futureWatcher.waitForFinished();
     
     // Query the future to check if was canceled.
     qDebug() << "Canceled?" << futureWatcher.future().isCanceled();
 }
#endif
 
 
 
#endif
 
 
 
#ifdef BYPASS
 // Operation constructor
 Operation::Operation(QObject *parent)
     : QObject(parent), steps(0)
 {
     pd = new QProgressDialog("Operation in progress.", "Cancel", 0, 100);
     connect(pd, SIGNAL(canceled()), this, SLOT(cancel()));
     t = new QTimer(this);
     connect(t, SIGNAL(timeout()), this, SLOT(perform()));
     t->start(0);
 }
 
 void Operation::perform()
 {
     pd->setValue(steps);
     //... perform one percent of the operation
     steps++;
     if (steps > pd->maximum())
         t->stop();
 }
 
 void Operation::cancel()
 {
     t->stop();
     //... cleanup
 }
 
 
#endif

And here is my current output

QDEBUG TRACE START void TaskDialog::on_doTaskButton_clicked()
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_clicked
@line     111
 Setup # of iterations = toatal delay  10  seconds
 Setup # of iterations as vector array 
 Setup Create a QProgressDialog dialog - set paramaters 
 Setup Create a QFutureWatcher
 setup futureWatcher and dialog connect SIGNAL  SLOT 
 setup future WatcherSIGNAL(finished()
 setup dialog, SIGNAL(canceled()
 Start the computation - 
apply delay function spin to each vector
 RUN dialog.exec() Display the dialog and start the dialog event loop
 START dialog.exec() 
futureWatcher.progressValue()  0
Estimated single iteration delay elapsed time  1001  mS
iteration #  0 in thread 0x7f6db5c91700
Estimated single iteration delay elapsed time  1001  mS
iteration #  2 in thread 0x7f6d9e581700
Estimated single iteration delay elapsed time  1004  mS
iteration #  1 in thread 0x7f6d9d57f700
Estimated single iteration delay elapsed time  1001  mS
iteration #  3 in thread 0x7f6d9dd80700
Estimated single iteration delay elapsed time  1001  mS
iteration #  4 in thread 0x7f6db5c91700
Estimated single iteration delay elapsed time  1001  mS
iteration #  6 in thread 0x7f6d9d57f700
Estimated single iteration delay elapsed time  1004  mS
iteration #  5 in thread 0x7f6d9e581700
Estimated single iteration delay elapsed time  1001  mS
iteration #  7 in thread 0x7f6d9dd80700
Estimated single iteration delay elapsed time  1001  mS
iteration #  8 in thread 0x7f6db5c91700
Estimated single iteration delay elapsed time  1001  mS
iteration #  9 in thread 0x7f6d9d57f700
futureWatcher.progressValue()  10
 END dialog.exec()  3034  mS

Note the last line - it should be approximately 10 seconds.

Pl45m4

@AnneRanch said in QFutureWatcher - timing issue:

Note the last line - it should be approximately 10 seconds.

Is this your only issue?! Are you aware that QElapsedTimer only counts the seconds from last (re-)start?!
So if you restart the same timer multiple times, it measures the time from last start to end only.

Can you confirm that every single task needs about one 1 second?! Or is this output wrong and it only takes 3 secs for all 10 tasks, which should take 10?

Anonymous_Banned275

@Pl45m4 said in QFutureWatcher - timing issue:

@AnneRanch said in QFutureWatcher - timing issue:

Note the last line - it should be approximately 10 seconds.

Is this your only issue?! ''
YES

Are you aware that QElapsedTimer only counts the seconds from last (re-)start?!

YES

So if you restart the same timer multiple times, it measures the time from last start to end only.

Name specific time that is incorrectly restarted that way .

Can you confirm that every single task needs about one 1 second?!
YES
I am after 10 seconds delay, using 10 iterations that = approximately 10 * 1 seconds. The time precision is irrelevant.

Or is this output wrong and it only takes 3 secs for all 10 tasks, which should take 10?

YES

The desired execution of dialog.exec() is 10 seconds - the current execution takes approximately 3 seconds.

Here is a crazy idea
If I set the iteration to 50 - the total delay time is approximately 13
seconds.

If I set the iteration to 100 - the total delay time is approximately 25 seconds.

The "spin" delay runs in its own thread - which is not necessary since the delay is cumulative - no need for parallel processing.

BUT the dialog.exec() "uses" all four CPU cores ( as noted in the progress dialog text ) - hence four threads .
Thinking up-loud - since each iteration runs in four threads - is the delay really 1 second? Sounds really crazy...
Keeping in mind that I really do not have means monitoring the dialog.exec()
iterations.
Could that be the issue?

I should be able to track both SIGNALS - I 'll take a look how it can be done.

kshegunov

@AnneRanch said in QFutureWatcher - timing issue:

The "spin" delay runs in its own thread - which is not necessary since the delay is cumulative

In its own threads.

- no need for parallel processing.

Then why do you explicitly use parallel processing? ... then wonder why the time is approximately scaled by the number of pooled threads ... this is all very confusing ...

BUT the dialog.exec() "uses" all four CPU cores ( as noted in the progress dialog text ) - hence four threads .

QDialog::exec doesn't use any cores at all. Your QtConcurrent::map does.

Keeping in mind that I really do not have means monitoring the dialog.exec()
iterations.

There are no iterations. QDialog::exec waits for an event to appear in the event queue, if there's none it just sleeps until one happens to appear (be it a GUI event or a signal/slot meta-call - a.k.a. queued connection call).

Anonymous_Banned275

@kshegunov said in QFutureWatcher - timing issue:

@AnneRanch said in QFutureWatcher - timing issue:

The "spin" delay runs in its own thread - which is not necessary since the delay is cumulative

In its own threads.

- no need for parallel processing.

Then why do you explicitly use parallel processing? ... then wonder why the time is approximately scaled by the number of pooled threads ... this is all very confusing ...

As pointed out many times - I am following a tutorial.
I have also said that most of the tutorial steps are not commented WHAT they do . Basically blindly following the tutorial - and the result is obvious.
Confusing to you , frustrating to me.

BUT the dialog.exec() "uses" all four CPU cores ( as noted in the progress dialog text ) - hence four threads .

Which does not make sense.

QDialog::exec doesn't use any cores at all. Your QtConcurrent::map does.

Keeping in mind that I really do not have means monitoring the dialog.exec()
iterations.

I do not like to get sidteracked by niticking on sentic.
The QProgresDialog ( n tutorial ) outputs

dialog.setLabelText(QString("Progressing using %1 thread(s)...\nTODO Elapsed time %2  [mS] ")
                    .arg(QThread::idealThreadCount()).arg(timer.elapsed()));

So why should I question WHO is using the threads - dialog or QtConcurrent?

How does that leads to solution ?
I am not complaining about your comment, just trying to maintain some priorities in logic to find the problem.

> There are no iterations. QDialog::exec waits for an event to appear in the event queue, if there's none it just sleeps until one happens to appear (be it a GUI event or a signal/slot meta-call - a.k.a. queued connection call).

**OK THIS IS VERY GOOD POINT and IMPORTANT,

My test delay process is initialized by standard button push...
"" can somebody describe WHAT EVENT actually starts QProgressDialog::exec ?**

I am under the impression that QProgressDialog constructor does that.
Am I wrong ?

And HOW does the delay process continue from starting point ?

Secondly
so what are "iterations" for ?
They are passed to QProgressDialog constructor...

Challenge to group
Would somebody some up with old fashioned flow chart to put the process
from "button pushed" to "delay completed " ?
My verbal output track sort of does it , but obviously needs better explanations what each step does.

New crazy thought - the original tutorial code worked (!) but it used default
constructor - without any parameters passed to the class and without setting any parameters in code - just used all unpublished defaults.
With one of the defaults , forgot which one, the actual progress bar supposedly should show up AFTER 4 second delay .

In current failure mode the progress bar shows 10% (immediately) then shows 50% ( after about 3 seconds) - the percentage is exactly "4 seconds " between the updates when iteration is set to 10 !

kshegunov

@AnneRanch said in QFutureWatcher - timing issue:

As pointed out many times - I am following a tutorial.
I have also said that most of the tutorial steps are not commented WHAT they do . Basically blindly following the tutorial - and the result is obvious.

Then read in docs what they do so you understand it, at least that's my advice. QtConcurrent::map isn't an alien we need a team of scientists to talk to, right? Just look it up, that's what I do when I follow tutorials.

Confusing to you , frustrating to me.

Yes, yes, frustration leads to anger, anger leads to the dark side and all that. Less emotion, more practicality helps, I've found out.

I do not like to get sidteracked by niticking on sentic.

Actually you do, you just don't realize it. You have an unknown machine you're trying to figure out, but you claim you're not interested in how the cogs it's made of fit together. Should I mention such an approach is utterly futile?

The QProgresDialog ( n tutorial ) outputs

dialog.setLabelText(QString("Progressing using %1 thread(s)...\nTODO Elapsed time %2  [mS] ")
                    .arg(QThread::idealThreadCount()).arg(timer.elapsed()));

So? This is evaluated before the dialog is even shown to the screen and has nothing to do with the dialog itself.

So why shoudI question WHO is using the threads - dialog or QtConcurren ?

It should, so you know where the problem lies. If you don't understand where the error is, then you're not going to be able to fix it, ever.

How does that leads to solution?

I don't know exactly what kind of solution you expect as I can't seem to fathom the problem. You split and process some vector in several threads, I get that. But I don't get what times and delays and elapsed timers have to do with it ...

For reference, what's the output of the following snippet:

QObject::connect(&futureWatcher, &decltype(futureWatcher)::progressRangeChanged, [] (int from, int to) -> void  {
    qDebug() << "Map from " << from << " to " << to;
});
QObject::connect(&futureWatcher, &decltype(futureWatcher)::progressValueChanged, [] (int value) -> void  {
    qDebug() << "Map progress: " << value;
});

Anonymous_Banned275

Assuming the QprogressDialog is advanced / controlled by QFutureWacher SIGNALs of :"value" and "range"

I have added means of monitoring these signals

 // create test SLOT to monitor progressValueChanged(int)

qDebug() << "create test SLOT to monitor progressValueChanged(int)";
QObject::connect(&futureWatcher, SIGNAL(progressValueChanged(int)), this, SLOT(on_doTaskButton_2_clicked));
QObject::connect(&futureWatcher, SIGNAL(progressRangeChanged(int,int)),this, SLOT(on_doTaskButton_3_clicked)));

The result output is here

 Start the computation - 
apply delay function spin to each vector
 RUN dialog.exec() Display the dialog and start the dialog event loop
 START dialog.exec() 
futureWatcher.progressValue()  0
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  0
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  1
Estimated single iteration delay elapsed time  1001  mS
iteration #  0 in thread 0x7f380b7fe700
Estimated single iteration delay elapsed time  1001  mS
iteration #  1 in thread 0x7f37fbfff700
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  2
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  3
Estimated single iteration delay elapsed time  1001  mS
iteration #  2 in thread 0x7f3808eea700
Estimated single iteration delay elapsed time  1008  mS
iteration #  3 in thread 0x7f37fb7fe700
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  4
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  5
Estimated single iteration delay elapsed time  1001  mS
iteration #  5 in thread 0x7f37fbfff700
Estimated single iteration delay elapsed time  1008  mS
iteration #  4 in thread 0x7f380b7fe700
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  6
Estimated single iteration delay elapsed time  1001  mS
iteration #  6 in thread 0x7f3808eea700
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  7
Estimated single iteration delay elapsed time  1001  mS
iteration #  7 in thread 0x7f37fb7fe700
Estimated single iteration delay elapsed time  1001  mS
iteration #  8 in thread 0x7f37fbfff700
Estimated single iteration delay elapsed time  1001  mS
iteration #  9 in thread 0x7f380b7fe700
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  8
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  9
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  10
QDEBUG TRACE track  SIGNAL SLOT
file      ../CAT_V1/configuredialog.cpp
function  on_doTaskButton_2_clicked
@line     512
 SLOT value access  11
futureWatcher.progressValue()  10
 END dialog.exec()  3030  mS

Conclusion
the SIGNAL monitoring the value is changed 11 times - pretty much what is expected. I'll add showing the actual "value" at each time int changes - just to further verify it - it should be 10, 20, 30 etc.

The range does not change and it should not - should remain 0 thru 100.

kshegunov

@AnneRanch said in QFutureWatcher - timing issue:

The range does not change and it should not - should remain 0 thru 100.

I somehow doubt that assertion, more specifically the numbers you cite, and the conclusions you draw from it. This is why I requested the output from the snippet in my previous post.

Anonymous_Banned275

"Programs written with QtConcurrent automatically adjust the number of threads used according to the number of processor cores available. "

Hence there is no single usage of QFuture vectors - but FOUR of them are used running in four CPU cores at once.
Hence QProgressDialog "runs out" the correctly timed iterations FOUR times faster.
Thus the total desired time delay is incorrect.

Pl45m4

@AnneRanch said in QFutureWatcher - timing issue:

FOUR times faster.

Four threads won't increase the processing time of your whole task by a factor of four (if they share the same data)

Might be interesting:
(esp. the Concurrent part)

https://www.logicbig.com/quick-info/programming/multi-threading.html

Anonymous_Banned275

@Pl45m4 said in QFutureWatcher - timing issue:

@AnneRanch said in QFutureWatcher - timing issue:

FOUR times faster.

Four threads won't increase the processing time of your whole task by a factor of four (if they share the same data)

Might be interesting:
(esp. the Concurrent part)

https://www.logicbig.com/quick-info/programming/multi-threading.html

Hence there is no single usage of QFuture vectors - but FOUR of them are used running in four CPU cores at once.
Hence QProgressDialog "runs out" the correctly timed iterations FOUR times faster.
Thus the total desired time delay is incorrect.

SGaist

@AnneRanch said in QFutureWatcher - timing issue:

Hence there is no single usage of QFuture vectors - but FOUR of them are used running in four CPU cores at once.
Hence QProgressDialog "runs out" the correctly timed iterations FOUR times faster.
Thus the total desired time delay is incorrect.

You are using the wrong assumption that the four cores of your machine are each running exclusively one of these tasks.

They are not. Your processor cores are shared and runs variety of tasks from which your application and its threads.

Just take a look at your platform system analyser. You'll see that there's a lot happening under the hood.

kshegunov

@AnneRanch said in QFutureWatcher - timing issue:

Hence there is no single usage of QFuture vectors - but FOUR of them are used running in four CPU cores at once.

Hm, very weird, if only someone had mentioned this before ...!

Hence QProgressDialog "runs out" the correctly timed iterations FOUR times faster.

Approximately. Which is the whole point of running anything in parallel.

Thus the total desired time delay is incorrect.

There's no such thing, I believe I already said that on more than one occasion. GUI programming is event driven, there's no specific time for waiting, or specific order in which things happen; you get events, you respond to events, this is all. If it takes 3 seconds or 5, or 10 seconds or an hour is beside the point. When the event/signal is sent/emitted, then you process it and this is all ...

@SGaist said in QFutureWatcher - timing issue:

You are using the wrong assumption that the four cores of your machine are each running exclusively one of these tasks.

It's possible, albeit rather rare.

@Pl45m4 said in QFutureWatcher - timing issue:

Four threads won't increase the processing time of your whole task by a factor of four (if they share the same data)

Actually, they should. They usually don't as per Amdahl's law. I've a piece I'd written for work that scales almost perfectly with the number of cores, however the task I'd implemented is such that it is extremely parallelizable.

Pl45m4

@kshegunov said in QFutureWatcher - timing issue:

Actually, they should. They usually don't as per Amdahl's law. I've a piece I'd written for work that scales almost perfectly with the number of cores, however the task I'd implemented is such that it is extremely parallelizable.

If you use threads on all your processor cores, at least some of them have other tasks to do (OS background services etc.), so you will always lose some msec to a few secs or am I wrong?