QtConcurrent - how do I verify - "all the ducks in the row "? revised

[k5054]

Member 14968771 wrote:

QTconcurent will not accept more than 5 parameters,

What's your source for this statement. The docs [Concurrent Run | Qt Concurrent 5.15.8](https://doc.qt.io/qt-5/qtconcurrentrun.html) do not mention any limit. Assuming that its a C++ template using a parameter pack, the only limit I would expect would be your pthread stack size, which defaults to 8M, so for all intents an purposes not an issue. One thing I would note is that hci_inquiry returns an int so I think the template parameter to QFuture should probablby be: QFuture future = QTconcurrent::run( ... )

Keep Calm and Carry On

[trønderen]

Member 14968771 wrote:

QTconcurent will not accept more than 5 parameters

Reminds me of when I worked for a company about to publish a completely rewritten FORTRAN compiler: The release was pushed by one (significant) customer who had run into the old compiler's limit on 99 (ninety-nine) parameters to one function. The new compiler would allow 128 parameters, but it could easily be extended to 256 in future compiler versions. I sort of accept that when going above a certain limit (isn't it 4 for the ARM ABI?), there is an increased cost. Five is probably acceptable. The day it grows beyond 99, I think you are on the wrong track :-)

[Lost User]

I got this second hand and did not bother to verify the parameters # limit. I am busy rebuilding my text code and will be able to try the function without std::bind. Well - until I can get pass the errors I really do not care if the return values is wrong. That puts me back to the original post - how do I know which is causing the error - wrong parameters , wrong # of parameters , incorrect return ... all of these are C++_ issues , very little to do with QT. ( ...but for some who cannot read it looks as QT problem...) Cheers

[Lost User]

Here us my latest test code it does prove that Qt Concurrent takes max of five "arguments" and lets leave it be... Secondly I found the "ducks" error. And not sure how to react to it. QT passes "arguments" to the run function , then QT expect / does this ( as a example ) int integer = 5; if the argument is of "TYPE" integer. ( I have not tried to assign any arbitrary symbol ) then QT expect the symbol "integer" to passed as (??) to the "run" function... ..and it it fails , it identifies the failure source as "TYPE" not as parameter or argument - just "TYPE"... Maybe that is normal , but what a pain to debug.

     extern int bFunction(
                    int arg1,
                    int arg2,
                    int arg3,
                    int arg4,
                    int arg5,
                    int arg6,
                    int arg7,
                    int arg8
                    );
        int integer = 5;
        
        QFuture future = QtConcurrent::run(
                    std::bind(
                        bFunction,
                        integer,
                        integer,
                        integer,
                        integer,
                        integer,
                        integer,
                        integer,
                        integer
                        )
                    );

[Lost User]

I merely said, "the documentation suggests ...". I do not have Qt on my system so I am not able to test it.

[Lost User]

Member 14968771 wrote:

( ...but for some who cannot read it looks as QT problem...)

Adding comments like that is unnecessary, and does not encourage people to help further.

[k5054]

It reminds me of an adage or axiom or some such that my prof stated in class back in university days that went something like "If you function has more than 5 parameters, you've forgotten one!"

Keep Calm and Carry On

[k5054]

Did some testing of my own over the weekend and I can confirm that QtConcurrent::run() does not like more than 5 parameters. Maybe the thing to do is to look into std::async, std::future as it does not seem to be limited and provides the same functionality. There's a couple of videos on them here: [C++ Weekly - Ep 9 std::future Quick-Start - YouTube](https://www.youtube.com/watch?v=iCL6GYoi1RU&list=PLs3KjaCtOwSZ2tbuV1hx8Xz-rFZTan2J1&index=9) and here: [C++ Weekly - Ep 11 std::future Part 2 - YouTube](https://www.youtube.com/watch?v=ZgN1-i095QY&list=PLs3KjaCtOwSZ2tbuV1hx8Xz-rFZTan2J1&index=11). Unless there's something in QtConcurrent that ties in better with your QT project, std::async and std::future may server you better. As a point of interest, why QT? If you're on Ubuntu, and not using Kubuntu, I would have thought that maybe GTK+ would provide a more consistent look-&-feel. There are C++ bindings available (gtkmm), so if you're on a QT/C++ learning curve it would be about the same for you. There's no integrated IDE with gtk, but there's plenty of IDE's out there that will play nicely. Or you could go "hardcore" and learn how to write Makefiles!

Keep Calm and Carry On

[Lost User]

I appreciate confirmation of the parameters # limit . I do not see why QT limitation of one process would be a reason to switch OS, especially when using std::bind "fixes " this limitation. I have SUCCESSFULLY codded and run several test function using QTConcurrent, and I am basically back where I started. I could use some more assistance with this. The attached code is direct from QT documentation. What I do not understand is the necessity of highlighted code. What is the purpose and is there a doc I could RTFM to get some understanding why this code is necessary. If I pass the aFunctionWithArguments function arguments at face value I then get the "type" error ( as posted previously ) Is this something "just QT " or is that "normal" C++ and if so what is the correct terminology of doing this ? I just call it "SYMBOLS". My real code gets complicated because I am a passing more the 5 "arguments" and two of them are pointer and double pointer. I can run my test function passing struct and have no need for these "SYMBOLS". I am NOT asking to write my code, I am asking for explanation why QT is using these "conversions / symbols "

extern void aFunctionWithArguments(int arg1, double arg2, const QString &string);

int integer = ...;
double floatingPoint = ...;
QString string = ...;

QFuture future = QtConcurrent::run(aFunctionWithArguments, integer, floatingPoint, string);

[Lost User]

As a debugging note if just the number of parameters passed, irregardless if the are "plain arguments" or these funky symbols do not match - the error is "run" " cannot find the function " . The "TYPE" error is definitely my wrong way of "symbolizing" the pointers. Unfortunately the error does not clearly identify which "symbol" is not correct. I'll try to find a real hci function which does not use pointers to verify this assumption.

[Lost User]

Here is "semifinal " version of WORKING code

   //int status = hci\_inquiry(adapter\_id, inquiry\_length,
    //max\_devices, NULL, &inq\_inf,flags );
    int status = 10;
    qDebug() << "Status " << QString::number(status);
    time->start();
    status =       hci\_inquiry(
                dev\_id,
                len,
                max\_rsp,
                NULL,
                &ii,
                flags);
    time->start();
    // run QtConcurent
    QFuture future = QtConcurrent::run(
                std::bind(
                    hci\_inquiry,
                    dev\_id,
                    len,
                    max\_rsp,
                    lap,     //NULL,
                    &ii,
                    flags)
                );
   //TOK 
   future.waitForFinished();  // test only need QTFutureWatcher
   qDebug() <<"hci\_inquiry elapsed time  " <elapsed());
   qDebug() <<"hci\_inquiry result  " <

I STILL do not understand why "plain function : usage " works with "lap" as NULL and QtConcurent usage DOES NOT. As I said before - I am not so sure I have only one version of hci_inquiry....

The be truthful - I need to get back to source code and try to build my own description for the hci_inquiry code.

It has been educational so far....

PS by semifinal - I need to "move" the QT version to its own object / library.

[k5054]

Try using nullptr instead of NULL. NULL is defined as a macro, often the equivalent of #define NULL ((void *)0). That was fine for C, but C++ has stricter rules about converting to/from NULL pointers, so you should use nullptr, particularly when you want to pass a null pointer to a function.

Keep Calm and Carry On