Class OrderedQueueList reference

Description
API reference

Description

OrderedQueueList is a utility class that sorts the events in an EventQueue in certain order.
With OrderedQueueList, we can dispatch events in certain order such as in priority order.
This class is used with the QueueList policy. See document of policies for details and how to implement new QueueList.

Warning: OrderedQueueList is not efficient since it simply inherits from std::list and sorts the full list on each splice. To use it in performance critical applications, you should implement your own version with sophisticated algorithm.

API reference

Header

eventpp/utilities/orderedqueuelist.h

Template parameters

template <typename Item, typename Compare = OrderedQueueListCompare>
class OrderedQueueList;

Item is used by the policies.
Compare is the comparison function object.
Its default implementation OrderedQueueListCompare looks like,

struct OrderedQueueListCompare
{
    template <typename T>
    bool operator() (const T & a, const T & b) const {
        return a.event < b.event;
    }
};

The typename T is actually the EventQueue::QueuedEvent. But since OrderedQueueList is used in the policies that are used to construct the EventQueue, it's not possible to specify the actual type in OrderedQueueListCompare, so here we use a template operator.

EventQueue::QueuedEvent is declared as,

struct QueuedEvent
{
    EventType event;
    std::tuple<Args> arguments;
};

event is the event sent to the queue.
arguments are the arguments that passed to EventQueue::enqueue.

Sample code

// First let's define the event struct. e is the event type, priority determines the priority.
struct MyEvent
{
    int e;
    int priority;
};

// The comparison function object used by eventpp::OrderedQueueList.
// The function compares the event by priority.
struct MyCompare
{
    template <typename T>
    bool operator() (const T & a, const T & b) const {
        return std::get<0>(a.arguments).priority > std::get<0>(b.arguments).priority;
    }
};

// Define the EventQueue policy
struct MyPolicy
{
    template <typename Item>
    using QueueList = eventpp::OrderedQueueList<Item, MyCompare >;

    static int getEvent(const MyEvent & event) {
        return event.e;
    }
};

void main()
{
    using EQ = eventpp::EventQueue<int, void(const MyEvent &), MyPolicy>;
    EQ queue;

    queue.appendListener(3, [](const MyEvent & event) {
        std::cout << "Get event " << event.e << "(should be 3)." << " priority: " << event.priority << std::endl;
    });
    queue.appendListener(5, [](const MyEvent & event) {
        std::cout << "Get event " << event.e << "(should be 5)." << " priority: " << event.priority << std::endl;
    });
    queue.appendListener(7, [](const MyEvent & event) {
        std::cout << "Get event " << event.e << "(should be 7)." << " priority: " << event.priority << std::endl;
    });

    // Add an event, the first number 5 is the event type, the second number 100 is the priority.
    // After the queue processes, the events will be processed from higher priority to lower priority.
    queue.enqueue(MyEvent{ 5, 100 });
    queue.enqueue(MyEvent{ 5, 200 });
    queue.enqueue(MyEvent{ 7, 300 });
    queue.enqueue(MyEvent{ 7, 400 });
    queue.enqueue(MyEvent{ 3, 500 });
    queue.enqueue(MyEvent{ 3, 600 });

    queue.process();
}

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