Issue with threading and opencv

[Kira]

@J-Hilk : will try and also i tried to run the program in debug mode and getting the following error.

Debugger redirects to following line of file of ostream:
// MANIPULATORS
template<class _Elem,
class _Traits> inline
basic_ostream<_Elem, _Traits>&
__CLRCALL_OR_CDECL endl(basic_ostream<_Elem, _Traits>& _Ostr)
{ // insert newline and flush stream
_Ostr.put(_Ostr.widen('\n'));
_Ostr.flush();
return (_Ostr);
}

And the program quits.
Can u please explain what may be the relevant reason for error

[jsulm]

@Kira Please post the stack trace after crash

[Kira]

@jsulm : I thought this is the stack trace after crash

[jsulm]

@Kira said in Issue with threading and opencv:

this is the stack trace after crash

no, it isn't

[Kira]

@jsulm : This is the only thing which i see after crash with exception triggered.
Is there any other way to do so

[jsulm]

@Kira In QtCreator if you start with debugger you will have a stack trace

[Kira]

@jsulm : Are you referring to this:

Please let me know in case of any issues

[jsulm]

@Kira Yes. Now you need to go from top to bottom until you hit first source code file from your project and check it at the line mentioned in the stack trace.

[Kira]

@jsulm : I tried doing it but the error is expected to come after thread running >150 times which is making the debugging process very difficult.
I have also sample test case on github can you please go through it for any possible issues.
https://github.com/HackersSpirit/ImageProcessor

[J.Hilk]

@Kira said in Issue with threading and opencv:

150 times

you can tell a breakpoint to be ignored for a certain amount of time

[jsulm]

@Kira I actually suggested to go through the stack trace after crash from top to bottom. No break points needed for that.

[Kira]

@jsulm :
@Kira said in Issue with threading and opencv:

@jsulm : Are you referring to this:

Please let me know in case of any issues

This is the stack trace which i get posted earlier referring from line no 1. It does not point to line of code where program has a break.
But line 16 and 17 point to the line of the code.
Should i refer those line for particular cause of the program to break
Please do let me know if i getting something wrong

[jsulm]

@Kira Check your code in that source code at line 16 and 17.

[Kira]

@jsulm :
Line 16 is pointing to following line in bold:
void ImageMapping::requestReWorkNew()
{
cout<<"Inside requestRework Newwwwwwwwww"<<endl;
const int sleep = 50;
int queueSize = queueImageName.size();
cout<<"Queue size Request Rework New: "<<queueSize<<endl;
if(queueImageName.size()!=0){
//Get the current image number from the list of images
mutex.lock();
_working = true;
_abort = false;
mutex.unlock();
cout<<"Emiting resume work"<<endl;
emit resumeWork();
}else{
cout<<"Signalling retrying"<<endl;

    emit retrying();
}

}

This function is basically a slot triggered by following signal:
connect(imageMapping, SIGNAL(finished()), imageMapping, SLOT(requestReWorkNew()));
connect(imageMapping, SIGNAL(retrying()),imageMapping,SLOT(requestReWorkNew()));

[jsulm]

@Kira Are you sure this is the line? The actual line is mentioned in the "Line" column in the stack trace. So, it would be 2129.

[J.Hilk]

@Kira you can double click on the line (in QtCreator) of the stack trace and it will open the file at the correct line

[Kira]

@jsulm : Actually i have recreated the issue.the program i am referring now is from github. I have cross checked the line which I highlighted is the same. If u want i can repost the image

[Kira]

@J-Hilk @jsulm : guys have you gone through the code at github do you see any issue with the threading logic? :)

[Kira]

@J-Hilk @jsulm : Hello guys sorry for the late update i was working on the issue.
Would like to share the update.
I trimmed down the issue further by first commenting out all the cout statements as the logs which
was coming pointed to the ostream file of the cout.
So the call stack pointed out to the opencv file stating unable to save the image.
So i commented the save function to find any thing else was causing the issue. What i found that my program was still breaking and the call stack pointed to the thread function.
I placed a counter for the signal and slot of the thread and it was found that it executed 666 times approx before breaking.

[Kira]

@J-Hilk
@jsulm :Guys thanks for your support i finally figured where exactly the problem was:
There was issue with the logic which was used for implementation. As you can see the code on github.
Instead of requesting the task in the dowork function every time a signal is raised and an slot is called to execute the task.
This led to the calling of so many signals and slots within a given time that it caused the stack to overflow.
The issue will be resolved by removing the signal slot loop. This issue was top priority, a big learning curve for my future implementations in dealing with signal and slot mechanism.

Thanks for your support.
Just one last question which i would like to be answered which triggered with this implementation.

1. Is there any limitation of how much slots can reside at a given time on a stack?
   As per my observation at a given time 666 approx signal/slots calls were made after which the program crashed.
2. Is the slot entry is cleared or maintained on the stack after the execution and can be increase the size of stack or transfer it to heap?

Regards