#include <chrono>
#include <condition_variable>
#include <cstdio>
#include <thread>

std::condition_variable g_condition_variable;
std::mutex g_mutex;
int g_count;

char *g_char_ptr = nullptr;

void
barrier_wait()
{
    std::unique_lock<std::mutex> lock{g_mutex};
    if (--g_count > 0)
        g_condition_variable.wait(lock);
    else
        g_condition_variable.notify_all();
}

void
do_bad_thing_with_location(unsigned index, char *char_ptr, char new_val)
{
    unsigned what = new_val;
    printf("new value written to array(%p) and index(%u) = %u\n", char_ptr, index, what);
    char_ptr[index] = new_val;
}

uint32_t
access_pool (bool flag = false)
{
    static std::mutex g_access_mutex;
    static unsigned idx = 0; // Well-behaving thread only writes into indexs from 0..6.
    if (!flag)
        g_access_mutex.lock();

    // idx valid range is [0, 6].
    if (idx > 6)
        idx = 0;

    if (flag)
    {
        // Write into a forbidden area.
        do_bad_thing_with_location(7, g_char_ptr, 99);
    }

    unsigned index = idx++;

    if (!flag)
        g_access_mutex.unlock();
    return g_char_ptr[index];
}

void
thread_func (uint32_t thread_index)
{
    printf ("%s (thread index = %u) startng...\n", __FUNCTION__, thread_index);

    barrier_wait();

    uint32_t count = 0;
    uint32_t val;
    while (count++ < 15)
    {
        printf ("%s (thread = %u) sleeping for 1 second...\n", __FUNCTION__, thread_index);
        std::this_thread::sleep_for(std::chrono::seconds(1));

        if (count < 7)
            val = access_pool ();
        else
            val = access_pool (true);

        printf ("%s (thread = %u) after sleep access_pool returns %d (count=%d)...\n", __FUNCTION__, thread_index, val, count);
    }
    printf ("%s (thread index = %u) exiting...\n", __FUNCTION__, thread_index);
}


int main (int argc, char const *argv[])
{
    g_count = 4;
    std::thread threads[3];

    g_char_ptr = new char[10]{};

    // Create 3 threads
    for (auto &thread : threads)
        thread = std::thread{thread_func, std::distance(threads, &thread)};

    struct {
        int a;
        int b;
        int c;
    } MyAggregateDataType;

    printf ("Before turning all three threads loose...\n"); // Set break point at this line.
    barrier_wait();

    // Join all of our threads
    for (auto &thread : threads)
        thread.join();

    delete[] g_char_ptr;

    return 0;
}
