c++ - thread::hardware_concurrency() 检查返回零值

Question

我正在使用 RHEL 6 64 位并在四核处理器上的虚拟机上运行。我编写了以下程序来检查硬件可以处理的线程数。

#include <thread>
#include <iostream>

using namespace std;

int main()
{
    cout << thread::hardware_concurrency() << endl;
    return 0;
}

结果总是零，是什么原因造成的？

Answer 1

来自 cppreference :

Returns the number of concurrent threads supported by the implementation. The value should be considered only a hint.

还有:

Return value

number of concurrent threads supported. If the value is not well defined or not computable, returns ​0​.

因此 thread::hardware_concurrency() 不必为您提供任何准确信息。
“准”也是仁者见仁智者见智。如果我有两个支持超线程的内核，hardware_concurrency 应该返回 2 还是 4？