Simple producer/consumer queue

Preamble
A very simple example of a single producer/consumer using locks and move operations.

Code
[js]
template
class ProdCon
{
public:
void push(T&& w_)
{
scoped_lock lock{_mtx};
if (_q.empty())
{
_cv.notify_one();
}
_q.emplace(move(w_));
}

T pop()
{
unique_lock lock{_mtx};
_cv.wait(lock, [this](){ return !_q.empty(); } );
auto& w = _q.front();
_q.pop();
return move(w);
}
private:
queue _q;
mutex _mtx;
condition_variable _cv;
};
[/js]

Points to note are:

Objects of type T are only ever moved.

The queue is only signalled when it is empty for efficiency reasons.

Full code
[js]
#include
#include
#include
#include #include
using namespace std;

template
class ProdCon
{
public:
void push(T&& w_)
{
scoped_lock lock{_mtx};
if (_q.empty())
{
_cv.notify_one();
}
_q.emplace(move(w_));
}

T pop()
{
unique_lock lock{_mtx};
_cv.wait(lock, [this](){ return !_q.empty(); } );
auto& w = _q.front();
_q.pop();
return move(w);
}
private:
queue _q;
mutex _mtx;
condition_variable _cv;
};

//——————-TestCode———————–

static int widgetNum = 1;

class Widget
{
public:
Widget() : _widgetNum{widgetNum++} {}
Widget(const Widget&) = delete;
Widget& operator=(const Widget&) = delete;
Widget(Widget&&) = default;
Widget& operator=(Widget&&) = default;

int num() { return _widgetNum; }

private:
int _widgetNum;
};

void staticTest()
{
cout << "staticTest" << endl; widgetNum = 1; Widget w1, w2, w3, w4; ProdCon pc;

pc.push(move(w1));
pc.push(move(w2));

cout << pc.pop().num() << endl; cout << pc.pop().num() << endl; pc.push(move(w3)); cout << pc.pop().num() << endl; pc.push(move(w4)); cout << pc.pop().num() << endl; } void dynamicTest() { cout << "dynamicTest" << endl; widgetNum = 1; Widget w1, w2, w3, w4; ProdCon pc;

auto prod = [&](){ pc.push(move(w1)); pc.push(move(w2)); pc.push(move(w3)); pc.push(move(w4)); };
auto con = [&](){ for(int i = 1; i<=4; ++i) {cout << pc.pop().num() << endl;}; }; auto fut = async(launch::async, con); async(launch::async, prod); //wait for consumer fut.get(); } int main() { staticTest(); dynamicTest(); return 0; } [/js]