设置std :: threads的线程亲和力

Question

I am trying to figure out how to set the thread affinity of std::thread or boost::thread using the win32 API. I want to use the SetThreadAffinityMask function to pin each thread to a particular core in my machine.

I used the thread native_handle member function to obtain the thread handle that is provided to the SetThreadAffinityMask function. However, doing this results in the SetThreadAffinityMask function returning 0, indicating a failure to set thread affinity.

unsigned numCores = std::thread::hardware_concurrency();
std::vector<std::thread> threads(numCores);

for (int i = 0; i < numCores; i++)
{
    threads.push_back(std::thread(workLoad, i));
    cout << "Original Thread Affinity Mask: " << SetThreadAffinityMask(threads[i].native_handle() , 1 << i) << endl;

}

for (thread& t : threads)
{
    if (t.joinable())
        t.join();
}

Original Thread Affinity Mask: 0

Original Thread Affinity Mask: 0

Original Thread Affinity Mask: 0

Original Thread Affinity Mask: 0

Original Thread Affinity Mask: 0

Original Thread Affinity Mask: 0

Original Thread Affinity Mask: 0

...etc

Answer 1

Your problem is the intial setup of threads to contain numCores default-initialized entries. Your new (read: real) threads are pushed on the vector afterward, but you never index to them when setting affinity. Instead you index using i , which just hits the objects in the vector that aren't really running threads, prior to your real threads.

A corrected version that's actually run-worthy appears below:

#include <iostream>
#include <vector>
#include <thread>
#include <chrono>

#include <windows.h>

void proc(void)
{
    using namespace std::chrono_literals;
    std::this_thread::sleep_for(5s);
}

int main()
{
    std::vector<std::thread> threads;
    for (unsigned int i = 0; i < std::thread::hardware_concurrency(); ++i)
    {
        threads.emplace_back(proc);
        DWORD_PTR dw = SetThreadAffinityMask(threads.back().native_handle(), DWORD_PTR(1) << i);
        if (dw == 0)
        {
            DWORD dwErr = GetLastError();
            std::cerr << "SetThreadAffinityMask failed, GLE=" << dwErr << '\n';
        }
    }

    for (auto& t : threads)
        t.join();
}