Class EventQueue

3rdparty/libprocess/src/event_queue.hpp:68–246

A _multiple_ producer (MP) _single_ consumer (SC) event queue for a process. Note that we don't _enforce_ the MP/SC semantics during runtime but we have explicitly separated out the `Producer` interface and the `Consumer` interface in order to help avoid incorrect usage. Notable semantics: Consumers _must_ call `empty()` before calling `dequeue()`. Failing to do so may result in undefined behavi

// into the actor model because there will only ever be a single
// thread consuming an actors events at a time.
class EventQueue
{
public:
  EventQueue() : producer(this), consumer(this) {}

  class Producer
  {
  public:
    // Returns false if not enqueued; this means the queue
    // is decomissioned. In this case the caller retains
    // ownership of the event.
    bool enqueue(Event* event) { return queue->enqueue(event); }

  private:
    friend class EventQueue;

    Producer(EventQueue* queue) : queue(queue) {}

    EventQueue* queue;
  } producer;

  class Consumer
  {
  public:
    Event* dequeue() { return queue->dequeue(); }
    bool empty() { return queue->empty(); }
    void decomission() { queue->decomission(); }
    template <typename T>
    size_t count() { return queue->count<T>(); }
    operator JSON::Array() { return queue->operator JSON::Array(); }

  private:
    friend class EventQueue;

    Consumer(EventQueue* queue) : queue(queue) {}

    EventQueue* queue;
  } consumer;

private:
  friend class Producer;
  friend class Consumer;

#ifndef LOCK_FREE_EVENT_QUEUE
  bool enqueue(Event* event)
  {
    synchronized (mutex) {
      if (comissioned) {
        events.push_back(event);
        return true;
      }
    }

    return false;
  }

  Event* dequeue()
  {