QTimer::singleShot()'s syntax

[agarny]

@JKSH said in QTimer::singleShot()'s syntax:

See http://doc.qt.io/qt-5/threads-synchronizing.html It sounds like the high-level approach slows things down noticeably for you, so go with the low-level ones instead.

Yes, I am already using low-level synchronization primitives in parts of my code, and this is the approach I am thinking of taking here too.

[agarny]

Ok, on further investigation, the symptom described in my original message is not the result of a race condition. I agree that it is not to say that my code is free of race conditions, although I am relatively confident that it is. Not so much because of the quality of my code, but rather because of the way it is used. Now, I know it's not great, but that's the compromise I had to make for my code to be as fast as possible, something that is important for my application.

Anyway, among other things, my application can "run" mathematical models and, until recently, it could only render one run at a time. Recently, I have modified my application so that it could render multiple runs and this is where the problem was. I wasn't properly handling multiple runs and because of the low overhead associated with the new QTimer::singleShot syntax (compared with the old syntax), my application didn't render the end of some runs. I now "properly" handle multiple runs and everything works as expected (see here for those who had a look at my code before).

So, thanks all for your feedback, it was much appreciated. (Thanks @VRonin for your std::bind() suggestion, which I now use.)

[aha_1980]

@agarny said in QTimer::singleShot()'s syntax:

Now, I know it's not great, but that's the compromise I had to make for my code to be as fast as possible, something that is important for my application.

Are you really going to say that fast code must be buggy?

Good luck with newer versions of your project. It may work more or less now, but when you add functionality sooner or later all uncleanliness hits back.

[VRonin]

Mathematical model + race condition = quantum model I guess 🙂

[agarny]

@aha_1980 said in QTimer::singleShot()'s syntax:

@agarny said in QTimer::singleShot()'s syntax:

Now, I know it's not great, but that's the compromise I had to make for my code to be as fast as possible, something that is important for my application.

Are you really going to say that fast code must be buggy?

No, this is not what I am going to say otherwise I would have already said it.

I merely said that to get the speed I was after I felt the need to make some compromises and that I am aware of their limitations, hence I have done my best to ensure that my code doesn't result in a race condition, etc. Should I ever find a solution that is "cleaner" and as fast as my current solution, then I will clearly implement it.

(Thanks for the sarcasm.)

[kshegunov]

@aha_1980's point is that you're building a house of cards here. Even if you don't see the effects now it is going to bite you in the a$$ sometime along the road. Remember what I wrote before: "If it works, it's the hand of god", well that's what he and I both mean. It's your code in the end and you can conduct your business as you like, we just felt it's a rather weak argument to ignore the simmering reality because you couldn't get enough speed at the time. In the end the speed would not matter if you don't get correct results, would it?

[agarny]

@kshegunov: I do hear what you are both saying, believe it or not (see above my comment about ever finding a "cleaner" solution).

[Joe von Habsburg]

@agarny @JonB @aha_1980 @J-Hilk @JKSH @kshegunov @mrjj @VRonin

I would like to add condition to singleshot like that

bool youCanRun = true;

timer.singleShot(1000, this, &MyClass::mySlot, youCanRun );

// if youCanRun == true => singleshot will work
// else singleshot won't work

Note : "youCanRun" could be changed in singleshot waiting time

Is there any syntax or methot I could use?

[JKSH]

@Joe-von-Habsburg said in QTimer::singleShot()'s syntax:

@agarny @JonB @aha_1980 @J-Hilk @JKSH @kshegunov @mrjj @VRonin

I would like to add condition to singleshot like that

bool youCanRun = true;

timer.singleShot(1000, this, &MyClass::mySlot, youCanRun );

// if youCanRun == true => singleshot will work
// else singleshot won't work

Note : "youCanRun" could be changed in singleshot waiting time

Is there any syntax or methot I could use?

Use a lambda. Check the value of youCanRun and call your slot if it is true.

bool youCanRun = true; // NOTE: This variable must not go out-of-scope before the timer is triggered

QTimer::singleShot(1000, this, [&]{
    if (youCanRun)
        this->mySlot();
    else
        qDebug("You cannot run!");
});

[Joe von Habsburg]

@JKSH thank you :)