Assigment5DoubleCheckedLockingReprise.cpp

#include <mutex>
#include <thread>
#include <vector>
#include <atomic>

using namespace std;

class some_type {
	// ...
public:
	void do_it() { /*...*/ }
};

atomic<some_type*> ptr{ nullptr };            // Variable to be lazily initialized
std::mutex process_mutex;

void process() {
	if (!ptr) {                                                                                  // First check of ptr
		std::lock_guard<std::mutex> lk(process_mutex);

		if (!ptr)                  // Second check of ptr
			ptr = new some_type;   // Initialize ptr
	}
	some_type* sp = ptr;
	sp->do_it();
}

int main() {
	vector<thread> threads;

	for (int i = 0; i < 10; ++i)
		threads.push_back(thread{ process });
	for (auto& t : threads)
		t.join();
}