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#pragma once
#include <Access/IAccessEntity.h>
#include <base/scope_guard.h>
#include <list>
#include <queue>
#include <unordered_map>
namespace DB
{
/// Helper class implementing subscriptions and notifications in access management.
class AccessChangesNotifier
{
public:
AccessChangesNotifier();
~AccessChangesNotifier();
using OnChangedHandler
= std::function<void(const UUID & /* id */, const AccessEntityPtr & /* new or changed entity, null if removed */)>;
/// Subscribes for all changes.
/// Can return nullptr if cannot subscribe (identifier not found) or if it doesn't make sense (the storage is read-only).
scope_guard subscribeForChanges(AccessEntityType type, const OnChangedHandler & handler);
template <typename EntityClassT>
scope_guard subscribeForChanges(OnChangedHandler handler)
{
return subscribeForChanges(EntityClassT::TYPE, handler);
}
/// Subscribes for changes of a specific entry.
/// Can return nullptr if cannot subscribe (identifier not found) or if it doesn't make sense (the storage is read-only).
scope_guard subscribeForChanges(const UUID & id, const OnChangedHandler & handler);
scope_guard subscribeForChanges(const std::vector<UUID> & ids, const OnChangedHandler & handler);
/// Called by access storages after a new access entity has been added.
void onEntityAdded(const UUID & id, const AccessEntityPtr & new_entity);
/// Called by access storages after an access entity has been changed.
void onEntityUpdated(const UUID & id, const AccessEntityPtr & changed_entity);
/// Called by access storages after an access entity has been removed.
void onEntityRemoved(const UUID & id, AccessEntityType type);
/// Sends notifications to subscribers about changes in access entities
/// (added with previous calls onEntityAdded(), onEntityUpdated(), onEntityRemoved()).
void sendNotifications();
private:
struct Handlers
{
std::unordered_map<UUID, std::list<OnChangedHandler>> by_id;
std::list<OnChangedHandler> by_type[static_cast<size_t>(AccessEntityType::MAX)];
std::mutex mutex;
};
/// shared_ptr is here for safety because AccessChangesNotifier can be destroyed before all subscriptions are removed.
std::shared_ptr<Handlers> handlers;
struct Event
{
UUID id;
AccessEntityPtr entity;
AccessEntityType type;
};
std::queue<Event> queue;
std::mutex queue_mutex;
std::mutex sending_notifications;
};
}
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