Implement producer/consumer (multiple producers, multiple consumers) problem with buffer size = 10.

cpp_producer_consumer.cpp

/**
        C++ Producer Consumer using C++11 thread facilities
        To compile: g++ -std=c++11 <program name> -pthread -lpthread -o pc
*/
#include <iostream>
#include <sstream>
#include <vector>
#include <stack>
#include <thread>
#include <mutex>
#include <atomic>
#include <condition_variable>
#include <chrono>
using namespace std;
 
// print function for "thread safe" printing using a stringstream
void print(ostream& s) { cout << s.rdbuf(); cout.flush(); s.clear(); }
 
//
//      Constants
//
const int num_producers = 5;
const int num_consumers = 10;
const int producer_delay_to_produce = 10;   // in miliseconds
const int consumer_delay_to_consume = 30;   // in miliseconds
 
const int consumer_max_wait_time = 200;     // in miliseconds - max time that a consumer can wait for a product to be produced.
 
const int max_production = 10;              // When producers has produced this quantity they will stop to produce
const int max_products = 10;                // Maximum number of products that can be stored
 
//
//      Variables
//
atomic<int> num_producers_working(0);       // When there's no producer working the consumers will stop, and the program will stop.
stack<int> products;                        // The products stack, here we will store our products
mutex xmutex;                               // Our mutex, without this mutex our program will cry
 
condition_variable is_not_full;             // to indicate that our stack is not full between the thread operations
condition_variable is_not_empty;            // to indicate that our stack is not empty between the thread operations
 
//
//      Functions
//
 
//      Produce function, producer_id will produce a product
void produce(int producer_id)
{
        unique_lock<mutex> lock(xmutex);
        int product;
 
        is_not_full.wait(lock, [] { return products.size() != max_products; });
        product = products.size();
        products.push(product);
 
        print(stringstream() << "Producer " << producer_id << " produced " << product << "\n");
        is_not_empty.notify_all();
}
 
//      Consume function, consumer_id will consume a product
void consume(int consumer_id)
{
        unique_lock<mutex> lock(xmutex);
        int product;
 
        if(is_not_empty.wait_for(lock, chrono::milliseconds(consumer_max_wait_time),
                [] { return products.size() > 0; }))
        {
                product = products.top();
                products.pop();
 
                print(stringstream() << "Consumer " << consumer_id << " consumed " << product << "\n");
                is_not_full.notify_all();
        }
}
 
//      Producer function, this is the body of a producer thread
void producer(int id)
{
        ++num_producers_working;
        for(int i = 0; i < max_production; ++i)
        {
                produce(id);
                this_thread::sleep_for(chrono::milliseconds(producer_delay_to_produce));
        }
 
        print(stringstream() << "Producer " << id << " has exited\n");
        --num_producers_working;
}
 
//      Consumer function, this is the body of a consumer thread
void consumer(int id)
{
        // Wait until there is any producer working
        while(num_producers_working == 0) this_thread::yield();
 
        while(num_producers_working != 0 || products.size() > 0)
        {
                consume(id);
                this_thread::sleep_for(chrono::milliseconds(consumer_delay_to_consume));
        }
 
        print(stringstream() << "Consumer " << id << " has exited\n");
}
 
//
//      Main
//
int main()
{
        vector<thread> producers_and_consumers;
 
        // Create producers
        for(int i = 0; i < num_producers; ++i)
                producers_and_consumers.push_back(thread(producer, i));
 
        // Create consumers
        for(int i = 0; i < num_consumers; ++i)
                producers_and_consumers.push_back(thread(consumer, i));
 
        // Wait for consumers and producers to finish
        for(auto& t : producers_and_consumers)
                t.join();
}

This line (97): while(num_producers_working != 0 || products.size() > 0); produce a race condition in method size