C++ thread request - c++

Question

I'm new to C++. In my application, there is a method getOnlineStatus():
int getOnlineStatus(int num);
This method is from third party DLL, it can't be modified.
I call this method to check number status, like this:
int num = 123456;
for (int i = 0; i < 10000000; i++) {
num = num + 1;
int nRet = getOnlineStatus(num);
if (nRet > 0) {
cout << num << "status online" << endl;
}
else if (nRet == 0) {
cout << num << "status offline" << endl;
}
else {
cout << num << "check fail" << endl;
}
}
But every time, it will take 2 seconds to return the nRet. So, if I check lots of number, it will take a long time.
Also, I tried to use async, but it's not working, it still takes 2 seconds to return a result one by one.
int num = 123456;
for (int i = 0; i < 10000000; i++) {
num = num + 1;
future<int> fuRes = std::async(std::launch::async, getOnlineStatus, num);
int result = fuRes.get();
if (result > 0) {
cout << num << "status online" << endl;
}
else if (result == 0) {
cout << num << "status offline" << endl;
}
else {
cout << num << "check fail" << endl;
}
}
Is there any way to open multiple threads to make it show results faster?

Answer 1

This largely depends on your third party DLL - does it even support requests from multiple threads? And if it does - do those requests use shared resources? Like the same internet connection / socket?
If you simplify your question and assume that the getOnlineStatus() sleeps for 2 seconds - then yes, you can greatly benefit from issuing multiple requests on different threads and wait in parallel.
Here is how you can simply setup reasonable number of threads to share the workload:
#include <iostream>
#include <vector>
#include <thread>
#include <chrono>
int status[10'000]{};
int getOnlineStatus(int n) {
std::this_thread::sleep_for(std::chrono::seconds(1));
return rand();
}
void getStatus(int low, int high) {
for (int i = low; i < high; i++) {
status[i] = getOnlineStatus(i);
}
}
int main()
{
srand(0);
const int count = std::thread::hardware_concurrency();
auto start = std::chrono::high_resolution_clock::now();
std::vector<std::thread> threads;
for (int i = 0, low = 0, high = 10; i < count; ++i, low += 10, high += 10)
threads.emplace_back(std::thread(getStatus, low, high));
for (auto& thread : threads)
thread.join();
auto stop = std::chrono::high_resolution_clock::now();
std::cout << count << " threads: " << std::chrono::duration_cast<std::chrono::milliseconds>(stop - start).count() << " ms" << std::endl;
start = std::chrono::high_resolution_clock::now();
for (int i = 0; i < 10 * count; ++i)
status[i] = getOnlineStatus(i);
stop = std::chrono::high_resolution_clock::now();
std::cout << "single thread: " << std::chrono::duration_cast<std::chrono::milliseconds>(stop - start).count() << " ms" << std::endl;
}
I get this result:
12 threads: 10075 ms
single thread: 120720 ms
NOTE: if those worker threads really do nothing, you can run many more of those, reducing total time significantly.