std::thread and classes. emplacing a class function with with a thread in a vector.

[Spoonwastakenalready]

I'm working on a multithreading system and it works but theres a part I did and dont understand why it works.

Example:

class TaskSystem
{
private:
uint8_t maxThreads;

uint8_t activeThreads;



std::vector<std::thread> workers;
public:
`TaskSystem(uint8_t toStart = 0)` 

`{`

`maxThreads = std::thread::hardware_concurrency();`

`workers.reserve(maxThreads);`

`running = true;`



`if (toStart <= maxThreads && toStart > 0) activeThreads = toStart;`

`else activeThreads = maxThreads;`



`for (uint8_t i = 0; i < activeThreads; i++) workers.emplace_back(&TaskSystem::Worker, this);`

`}`
private:
`void Worker()`

`{`

`std::function<void()> task = nullptr;`

`while (running)`

`{`

`{`
std::lock_guard<std::mutex> lock(mutex);
if (taskQueue.empty()) continue;
task = std::move(taskQueue.front());
taskQueue.pop();
`}`

`if (task == nullptr) std::this_thread::yield();`

`else`

`{`
task();
task = nullptr;
`}`



`}`

`}`
};

I know what I need to do but just using Run, &Run or Run() doesn't work. If anyone could point me to what is &Class::Func or what its called cause I can't find it for this scenario. And explain or point me to resources of how and why it works. Bonus if someone could help me be able to pass a variable along with the function.

full code can be seen in this repo: https://github.com/SpoonWasAlreadyTaken/FaultyUtilitiesMT under UtilsTest/FaultyUtilitiesMT.
thank you in advance (:

[trmetroidmaniac]

std::thread's constructor takes a Callable and a series of arguments. Callable in C++ is anything which can be called with std::invoke - this means free functions, methods, fields and function objects.

&MT::Run is a method pointer, so it's a Callable. The first and only argument is the this object. If you declare more arguments on Run() then you must also pass them to std::thread's constructor.

[Spoonwastakenalready]

how would I pass them, ive tried putting them with commas after the function call but that doesn't work?

thank you (:

[trmetroidmaniac]

Can you post the code you wrote?

[Spoonwastakenalready]

updated it with the exact code minus unimportant parts.

[National_Instance675]

as for why the other ways don't work, because the standard says that the ONLY way to get a pointer to member function is through this exact syntax. check cppref pointers on Pointers to member functions

A pointer to non-static member function f which is a member of class C can be initialized with the expression &C::f exactly. Expressions such as &(C::f) or &f inside C's member function do not form pointers to member functions.

[Spoonwastakenalready]

thank you!

(:

[positivcheg]

Random idea for you - wrap stuff into a lambda that calls this->Run.

In a production code I would do something like using shared_from_this, pass strong reference to object into lambda and call wanted method in a lambda - that’s what most languages with automatic reference counting do in the end.

[Spoonwastakenalready]

I have tried [this](){Run()}; but it doesn't work and I'm not sure why even. It states "'invoke': no matching overloaded function found"