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#pragma once
#include <unordered_map>
#include <unordered_set>
#include <mutex>
#include <memory>
#include <optional>
#include <Poco/Event.h>
#include "ZooKeeper.h"
#include "Common.h"
namespace DB
{
namespace ErrorCodes
{
}
}
namespace zkutil
{
/// This class allows querying the contents of ZooKeeper nodes and caching the results.
/// Watches are set for cached nodes and for nodes that were nonexistent at the time of query.
/// After a watch fires, the callback or event that was passed by the user is notified.
///
/// NOTE: methods of this class are not thread-safe.
///
/// Intended use case: if you need one thread to watch changes in several nodes.
/// If instead you use simple a watch event for this, watches will accumulate for nodes that do not change
/// or change rarely.
class ZooKeeperNodeCache
{
public:
explicit ZooKeeperNodeCache(GetZooKeeper get_zookeeper);
ZooKeeperNodeCache(const ZooKeeperNodeCache &) = delete;
ZooKeeperNodeCache(ZooKeeperNodeCache &&) = default;
struct ZNode
{
bool exists = false;
std::string contents;
Coordination::Stat stat{};
};
ZNode get(const std::string & path, EventPtr watch_event);
ZNode get(const std::string & path, Coordination::WatchCallback watch_callback);
private:
GetZooKeeper get_zookeeper;
struct Context
{
std::mutex mutex;
std::unordered_set<std::string> invalidated_paths;
bool all_paths_invalidated = false;
};
std::shared_ptr<Context> context;
std::unordered_map<std::string, ZNode> path_to_cached_znode;
};
}
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