Multithread C++ Modern

multithread_cpp.cpp

/*
*****************************************************************
*               THREADING - CHAPTER 1
*****************************************************************
*/

#include <chrono>
#include <iostream>
#include <memory>
#include <mutex>
#include <random>
#include <thread>
#include <vector>

using namespace std;

mutex       mtx, mvalue;
vector<int> values;

int randomValue(const int min, const int max) {
    static thread_local mt19937 generator(
        hash<thread::id>()(this_thread::get_id()));
    uniform_int_distribution<int> dist(min, max);
    return dist(generator);
}

void threadfunc(int tid) {
    mtx.lock();
    auto start = chrono::system_clock::now();
    cout << "Starting thread: " << tid << endl;
    mtx.unlock();

    mvalue.lock();
    int val = values[0];
    mvalue.unlock();
    int rval = randomValue(0, 10);
    val += rval;

    mtx.lock();
    cout << "Thread " << tid << " adding " << rval << ". New value: " << val
         << endl;
    mtx.unlock();

    mvalue.lock();
    values.push_back(val);
    mvalue.unlock();

    mtx.lock();
    chrono::duration<double> dur = chrono::system_clock::now() - start;
    cout << "\nThread[" << tid << "] time: " << dur.count() << "ms \n\n";
    mtx.unlock();
}

int main() {
    
    auto start = chrono::system_clock::now();
    values.push_back(42);
    cout << endl;
    vector<thread> vt;
    int n=1;
    vt.emplace_back(thread(threadfunc, n));
    n++;
    vt.emplace_back(thread(threadfunc, n));
    n++;
    vt.emplace_back(thread(threadfunc, n));
    n++;
    vt.emplace_back(thread(threadfunc, n));
    n++;
    vt.emplace_back(thread(threadfunc, n));
    n++;
    vt.emplace_back(thread(threadfunc, n));
    n++;
    vt.emplace_back(thread(threadfunc, n));
    n++;
    vt.emplace_back(thread(threadfunc, n));
    n++;
    vt.emplace_back(thread(threadfunc, n)); //n == 9
    cout << endl;

    for (auto& i : vt) {
        i.join();
    }

    cout << "Input: " << values[0] << ", Result 1: " << values[1]
         << ", Result 2: " << values[2] << ", Result 3: " << values[3] << endl;
    chrono::duration<long double> dur = chrono::system_clock::now() - start;
    cout << "\nTotal time: " << dur.count() << "ms \n\n";

    // return cin.get();
}

Example based in ebook ("Mastering Multithreading C++")