Best way to parallize this for loop with multiple threads

I currently have a code block like this

UINT8* u = getResult();
for (UINT64 counter = 0; counter < MaxCount; counter++)
{
    for (UINT64 index = 0; index < c_uOneMB; ++index)
    {
        *u++ = genValue();
    }
}

Now in order to make this run faster. I am doing something like this. Basically splitting the inner thread into a method. However I have two concerns which I am not sure how to tackle.

1. *u++ how do I handle that?
2. Before calling doSomethingElse() all the threads need to .join()

Any suggestions on how to accomplish that?

void doSomething(UINT8* u)
{
      for (UINT64 index = 0; index < c_uOneMB; ++index)
      {
          *u++ = genValue();
      }
}

UINT8* u = getResult();
for (UINT64 counter = 0; counter < MaxCount; counter++)
{
    std::thread t(doSomething,u);
}

doSomethingElse();

>Solution :

With little details you have provided I can give only this:

std::generate_n(std::execution::par, getResult(), MaxCount * c_uOneMB, genValue);

• https://en.cppreference.com/w/cpp/algorithm/generate_n
• https://en.cppreference.com/w/cpp/algorithm/execution_policy_tag