C ++：如何运行系统命令N次（异步）并返回N次执行时间？

Question

I'm new to C++ and have not used any threading in C++ yet. I'm on windows 7 using visual studio 2010.

What I'm trying to do is write a main method that triggers N executions of a given system command and for each execution it is able to acquire the time taken for that particular execution on completion. It would also be nice to know if the command succeeded or failed through getting the return code for that command and as a bonus getting the output back would be nice although not essential initially.

Now I know how to do most of this but given that I need to spawn N executions at the same time and given that each execution is likely to be long running I'm guessing it will need a thread per execution and this is what I'm not sure how to do.

For someone new to C++ threading would you please choose a threading implementation and library that you'd like to recommend and give me an example main method of how to do the above? I will be reading on C++ threading too subsequently (if you have any pointers on resources please let me know). Many thanks.

Answer 1

Here's a small program using the new threading functionality from C++11:

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

std::chrono::nanoseconds run_program_and_calculate_time()
{
    // TODO: Do your real stuff here
    return std::chrono::nanoseconds(5);
}

int main()
{
    constexpr int N = 5;

    std::vector<std::future<std::chrono::nanoseconds>> results(N);

    // Start the threads
    for (int i = 0; i < N; i++)
    {
        results[i] = std::async(std::launch::async,
                [](){ return run_program_and_calculate_time(); });
    }

    // Wait for all threads to be done results
    for (int i = 0; i < N; i++)
        results[i].wait();

    // Print results
    for (int i = 0; i < N; i++)
    {
        std::cout << "Result from " << i << ": "
                      << results[i].get().count() << " nanoseconds\n";
    }
}