ryanjeong / design-pattern

Gang of Four Design Patterns

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design-pattern's Issues

Thread-safe Singleton using unique_ptr

// singleton.cc
// g++ singleton.cc -std=c++11 -lboost_system
#include "singleton.hpp"

#include <iostream>

#include <boost/thread/thread.hpp>

std::unique_ptr<Singleton> Singleton::instance = nullptr;
std::once_flag Singleton::flag;

Singleton& Singleton::GetInstance() {
	std::call_once(Singleton::flag, []() {
      Singleton::instance.reset(new Singleton);
  });
	std::cout << "Get Instance." << std::endl;

	return *Singleton::instance;
}

int main() try {
  Singleton::GetInstance();
	Singleton::GetInstance();
	Singleton::GetInstance();

	return 0;
} catch (std::exception& e) {
	std::cout << e.what() << std::endl;
}

// singleton.hpp
#pragma once

#include <memory>  // unique_ptr
#include <mutex>  // once_flag

class Singleton final {
 public:
  ~Singleton() = default;
  Singleton(const Singleton&) = delete;
  Singleton(Singleton&&) = delete;
  Singleton& operator=(const Singleton&) = delete;
  Singleton& operator=(Singleton&&) = delete;
  static Singleton& GetInstance();

 private:
  Singleton() = default;
  static std::unique_ptr<Singleton> instance;
  static std::once_flag flag;
};

Waitfree Single-Producer/Single-Consumer Queue

Waitfree Single-Producer/Single-Consumer Queue

#include <boost/thread/thread.hpp>
#include <boost/lockfree/spsc_queue.hpp>
#include <iostream>

#include <boost/atomic.hpp>

int producer_count = 0;
boost::atomic_int consumer_count (0);

boost::lockfree::spsc_queue<int, boost::lockfree::capacity<1024> > spsc_queue;

const int iterations = 10000000;

void producer(void)
{
    for (int i = 0; i != iterations; ++i) {
        int value = ++producer_count;
        while (!spsc_queue.push(value))
            ;
    }
}

boost::atomic<bool> done (false);

void consumer(void)
{
    int value;
    while (!done) {
        while (spsc_queue.pop(value))
            ++consumer_count;
    }

    while (spsc_queue.pop(value))
        ++consumer_count;
}

int main(int argc, char* argv[])
{
    using namespace std;
    cout << "boost::lockfree::queue is ";
    if (!spsc_queue.is_lock_free())
        cout << "not ";
    cout << "lockfree" << endl;

    boost::thread producer_thread(producer);
    boost::thread consumer_thread(consumer);

    producer_thread.join();
    done = true;
    consumer_thread.join();

    cout << "produced " << producer_count << " objects." << endl;
    cout << "consumed " << consumer_count << " objects." << endl;
}