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#include <iostream>
#include <memory>
#include <thread>
#include <chrono>
#include <mutex>
struct Base
{
Base() { std::cout << " Base::Base()\n"; }
// Note: non-virtual destructor is OK here
~Base() { std::cout << " Base::~Base()\n"; }
};
struct Derived: public Base
{
Derived() { std::cout << " Derived::Derived()\n"; }
~Derived() { std::cout << " Derived::~Derived()\n"; }
};
void thr(std::shared_ptr<Base> p)
{
std::this_thread::sleep_for(std::chrono::seconds(1));
std::shared_ptr<Base> lp = p; // thread-safe, even though the
// shared use_count is incremented
{
static std::mutex io_mutex;
std::lock_guard<std::mutex> lk(io_mutex);
std::cout << "local pointer in a thread:\n"
<< " lp.get() = " << lp.get()
<< ", lp.use_count() = " << lp.use_count() << '\n';
}
}
int main()
{
std::shared_ptr<Base> p = std::make_shared<Derived>();
std::cout << "Created a shared Derived (as a pointer to Base)\n"
<< " p.get() = " << p.get()
<< ", p.use_count() = " << p.use_count() << '\n';
std::thread t1(thr, p), t2(thr, p), t3(thr, p);
p.reset(); // release ownership from main
std::cout << "Shared ownership between 3 threads and released\n"
<< "ownership from main:\n"
<< " p.get() = " << p.get()
<< ", p.use_count() = " << p.use_count() << '\n';
t1.join(); t2.join(); t3.join();
std::cout << "All threads completed, the last one deleted Derived\n";
}