event_bus.h

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#pragma once
 
#include "event_subscriber.h"
#include <functional>
#include <memory>
#include <mutex>
#include <shared_mutex>
#include <unordered_map>
 
namespace hgps {
 
class DefaultEventBus final : public EventAggregator {
  public:
    [[nodiscard]] std::unique_ptr<EventSubscriber>
    subscribe(EventType event_id,
              std::function<void(std::shared_ptr<EventMessage> message)> function) override;
 
    void publish(std::unique_ptr<EventMessage> message) const override;
 
    void publish_async(std::unique_ptr<EventMessage> message) const override;
 
    bool unsubscribe(const EventSubscriber &subscriber) override;
 
    [[nodiscard]] std::size_t count();
 
    void clear() noexcept;
 
  private:
    using mutex_type = std::shared_mutex;
    mutable mutex_type subscribe_mutex_;
    std::unordered_multimap<int, std::string> registry_;
    std::unordered_map<std::string, std::function<void(std::shared_ptr<EventMessage>)>>
        subscribers_;
 
    template <typename Callable> void shared_access(const Callable &callable) const {
        try {
            std::shared_lock<mutex_type> lock(subscribe_mutex_);
            callable();
        } catch (std::system_error &) {
            // do nothing
        }
    }
 
    template <typename Callable> void exclusive_access(const Callable &callable) const {
        try {
            std::unique_lock<mutex_type> lock(subscribe_mutex_);
            callable();
        } catch (std::system_error &) {
            // do nothing
        }
    }
};
} // namespace hgps