Using threads for dashing timers | Together C & C++ | Page 1

normal flame Jun 17, 2024, 2:33 PM

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Hello, I'm currently trying to create a basic 2d platformer in C++. Recently, I was trying to implement a dash using multithreading, to have its own timers.
However, I'm unable to get multi threading working.

I have the dash and movement options located in my "Player" class. Below is the code that is throwing the error, the dash code, and the errors.
Error:

void Player::events(SDL_Event& e)
{
    // If a key was pressed
    if (e.type == SDL_KEYDOWN && e.key.repeat == 0)
    {
        if (canSDash){
            switch (e.key.keysym.sym)
            {
                case SDLK_w: sDashDirection = 1; break;
                case SDLK_s: sDashDirection = 2; break;
                case SDLK_a: sDashDirection = 3; break;
                case SDLK_d: sDashDirection = 4; break;
            }
            //this is line 28
            std::thread t1(&Player::sDash, sDashDirection);
            t1.join;
        }
    }
}

sDash Code:

void Player::sDash(int direction) {
    canSDash = false;
    isSDashing = true;
    gravity = 0.0f;
    switch (direction){
        //up 
        case 1: break;
        //down
        case 2: break;
        //left
        case 3: break;
        //right
        case 4: break;
    }
    Sleep(sDashingTime*1000);
    gravity = 0.1f;
    Sleep(sDashingCooldown*1000);
    isSDashing = false;
    canSDash = true;
}

Errors:
.../Scripts/Player.cpp:28:58: required from here

.../bits/std_thread.h:157:72: error: static assertion failed:
std::thread arguments must be invocable after conversion to rvalues
157 | typename decay<_Args>::type...>::value,

twin lichenBOT Jun 17, 2024, 2:33 PM

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opal vessel Jun 17, 2024, 2:43 PM

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You basically never want threads for this. Threads are relatively heavyweight, you definitely don't want to have a thread per entity

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Maybe a coroutine would work ok here, but those have a problem of being hard-to-impossible to serialize, so adding a networking to this later would be a pain

normal flame Jun 17, 2024, 2:44 PM

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Networking is not in the plans

opal vessel Jun 17, 2024, 2:44 PM

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The reason why it doesn't compile, though, is because you need to give an instance of the Player class to std::thread. So probably like this:

std::thread t1(&Player::sDash, this, sDashDirection);

And you need to make sure the player is not moved around in memory, so it can't be e.g. a vector element if you add/remove elements

normal flame Jun 17, 2024, 2:46 PM

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what does "this" stand for?

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It does compile correctly now

opal vessel Jun 17, 2024, 2:47 PM

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In a method of a class, this is a pointer to the instance of the class the method is being called on

normal flame Jun 17, 2024, 2:48 PM

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I see

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And in regards to threads, the reason I chose them is because they are most similair to unity's "yield" function

opal vessel Jun 17, 2024, 2:49 PM

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I didn't work with unity, butyield sounds like something a coroutine would have

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Though using them in C++ without third-party libraries is a pain (you basically aren't expected to), so if you want them, you'll need to find some third-party library

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Something like this: https://github.com/jbaldwin/libcoro

normal flame Jun 17, 2024, 2:51 PM

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I will look into that. Thank you for the help

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!solved

twin lichenBOT Jun 17, 2024, 2:51 PM

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Thank you and let us know if you have any more questions!

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#Using threads for dashing timers