including unique_ptr in a threadsafe_queue

[bluefrog]

I'm trying to construct a small queue that only pushes and pops unique pointers.

I keep getting the following error:
error: no matching function for call to ‘threadsafe_queue<std::unique_ptr<tcp_session> >::push_unique(std::remove_reference<std::unique_ptr<tcp_session>&>::type)’

I've tried the following combinations of calls to push_unique:

  // q.push_unique(tcp_sess);
  q.push_unique(std::move(tcp_sess));

but both function calls result in the same error.

#include <queue>
#include <memory>
#include <mutex>
#include <condition_variable>

class tcp_session { // dummy session
  private:
    int socket;
  public:
    void set_x(int i) { socket = i;}
    int get_x() { return socket;}
};

template<typename T>
class threadsafe_queue {
  private:
    mutable std::mutex mut;
    std::queue<std::unique_ptr<T>> unique_ptr_q;
    std::condition_variable cv;
  public:
    threadsafe_queue() {}
    threadsafe_queue(const threadsafe_queue&) = delete;
    threadsafe_queue& operator=(const threadsafe_queue&) = delete;

    //void push_unique(std::unique_ptr<T> ptr) {
    void push_unique(std::unique_ptr<T>&& ptr) {
      std::lock_guard<std::mutex> lk(mut);
      unique_ptr_q.push(std::move<ptr>);
      cv.notify_one();
    }

    std::unique_ptr<T> pop_unique() {
      std::unique_lock<std::mutex> lk(mut);
      cv.wait(lk,[this]{return !unique_ptr_q.empty();});
      auto res =  std::make_unique<T>(unique_ptr_q.front()) ;
      unique_ptr_q.pop();
      return res;
    }

    bool empty() const {
      std::lock_guard<std::mutex> lk(mut);
      return unique_ptr_q.empty();
    }
};

int main()  {
  std::unique_ptr<tcp_session> tcp_sess;
  threadsafe_queue<std::unique_ptr<tcp_session>> q;

  tcp_sess->set_x(10);
  // q.push_unique(tcp_sess);
  q.push_unique(std::move(tcp_sess));
  
  auto tcp_sess2 = q.pop_unique();
  std::cout << "x " << tcp_sess2->get_x() "\n";
  return 0;
}

Can anybody suggest how to modify q.push_unique(std::move(tcp_sess)); or does the function declaration/definition need to change?

[JLBorges]

#include <queue>
#include <memory>
#include <mutex>
#include <condition_variable>
#include <iostream> // **************

class tcp_session { // dummy session
    private:
    int socket;
    public:
    void set_x( int i ) { socket = i; }
    int get_x() { return socket; }
};

template<typename T>
class threadsafe_queue {
    private:
    mutable std::mutex mut;
    std::queue<std::unique_ptr<T>> unique_ptr_q;
    std::condition_variable cv;
    public:
    threadsafe_queue() {}
    threadsafe_queue( const threadsafe_queue& ) = delete;
    threadsafe_queue& operator=( const threadsafe_queue& ) = delete;

    //void push_unique(std::unique_ptr<T> ptr) {
    void push_unique( std::unique_ptr<T>&& ptr ) {
        std::lock_guard<std::mutex> lk( mut );
        unique_ptr_q.push( std::move( ptr ) ); // **************
        cv.notify_one();
    }

    std::unique_ptr<T> pop_unique() {
        std::unique_lock<std::mutex> lk( mut );
        cv.wait( lk, [this] {return !unique_ptr_q.empty(); } );
        auto res = std::move( unique_ptr_q.front() ) ; // **************
        unique_ptr_q.pop();
        return res;
    }

    bool empty() const {
        std::lock_guard<std::mutex> lk( mut );
        return unique_ptr_q.empty();
    }
};

int main() {
    std::unique_ptr<tcp_session> tcp_sess = std::make_unique<tcp_session>() ; // **************
    threadsafe_queue<tcp_session> q; // **************

    tcp_sess->set_x(10);
    // q.push_unique(tcp_sess);
    q.push_unique( std::move( tcp_sess ) );

    auto tcp_sess2 = q.pop_unique();
    std::cout << "x " << tcp_sess2->get_x() << "\n"; // **************
    return 0;
}

http://coliru.stacked-crooked.com/a/c5022221a3f74126

[bluefrog]

many thanks

[bluefrog]

I have another query. When I run the example you posted, it works fine, but when I tried to integrate the above into the project I have, I came up with the following error:

// error: invalid application of ‘sizeof’ to incomplete type ‘tcp_session' 

when using either of the following 2 lines:

      auto tcp_sess = tcp_sess_q.pop_unique();
      //std::unique_ptr<tcp_session> tcp_sess = std::move(tcp_sess_q.pop_unique()); // blocks using a conditional variable with a unique_lock 

Any ideas why ?

[JLBorges]

#include the header which contains the definition of class tcp_session

If you had already done that, check the #include guards; make sure that they are correct.