ClickHouse/base/poco/Foundation/include/Poco/UniqueAccessExpireStrategy.h

//
// UniqueAccessExpireStrategy.h
//
// Library: Foundation
// Package: Cache
// Module:  UniqueAccessExpireStrategy
//
// Definition of the UniqueAccessExpireStrategy class.
//
// Copyright (c) 2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_UniqueAccessExpireStrategy_INCLUDED
#define Foundation_UniqueAccessExpireStrategy_INCLUDED


#include <map>
#include <set>
#include "Poco/AbstractStrategy.h"
#include "Poco/Bugcheck.h"
#include "Poco/EventArgs.h"
#include "Poco/KeyValueArgs.h"
#include "Poco/Timespan.h"
#include "Poco/Timestamp.h"
#include "Poco/UniqueExpireStrategy.h"
#include "Poco/ValidArgs.h"


namespace Poco
{


template <class TKey, class TValue>
class UniqueAccessExpireStrategy : public AbstractStrategy<TKey, TValue>
/// An UniqueExpireStrategy implements time based expiration of cache entries. In contrast
/// to ExpireStrategy which only allows to set a per cache expiration value, it allows to define
/// expiration per CacheEntry.
/// Each TValue object must thus offer the following method:
///
///    const Poco::Timestamp& getTimeout() const;
///
/// which returns the timespan for how long an object will be valid without being accessed.
{
public:
    typedef std::pair<TKey, Timespan> KeyExpire;
    typedef std::multimap<Timestamp, KeyExpire> TimeIndex;
    typedef typename TimeIndex::iterator IndexIterator;
    typedef typename TimeIndex::const_iterator ConstIndexIterator;
    typedef std::map<TKey, IndexIterator> Keys;
    typedef typename Keys::iterator Iterator;

public:
    UniqueAccessExpireStrategy()
    /// Create an unique expire strategy.
    {
    }

    ~UniqueAccessExpireStrategy() { }

    void onAdd(const void *, const KeyValueArgs<TKey, TValue> & args)
    {
        // the expire value defines how many millisecs in the future the
        // value will expire, even insert negative values!
        Timestamp expire;
        expire += args.value().getTimeout().totalMicroseconds();

        IndexIterator it = _keyIndex.insert(std::make_pair(expire, std::make_pair(args.key(), args.value().getTimeout())));
        std::pair<Iterator, bool> stat = _keys.insert(std::make_pair(args.key(), it));
        if (!stat.second)
        {
            _keyIndex.erase(stat.first->second);
            stat.first->second = it;
        }
    }

    void onRemove(const void *, const TKey & key)
    {
        Iterator it = _keys.find(key);
        if (it != _keys.end())
        {
            _keyIndex.erase(it->second);
            _keys.erase(it);
        }
    }

    void onGet(const void *, const TKey & key)
    {
        // get updates the expiration time stamp
        Iterator it = _keys.find(key);
        if (it != _keys.end())
        {
            KeyExpire ke = it->second->second;
            // gen new absolute expire value
            Timestamp expire;
            expire += ke.second.totalMicroseconds();
            // delete old index
            _keyIndex.erase(it->second);
            IndexIterator itt = _keyIndex.insert(std::make_pair(expire, ke));
            // update iterator
            it->second = itt;
        }
    }

    void onClear(const void *, const EventArgs & args)
    {
        _keys.clear();
        _keyIndex.clear();
    }

    void onIsValid(const void *, ValidArgs<TKey> & args)
    {
        Iterator it = _keys.find(args.key());
        if (it != _keys.end())
        {
            Timestamp now;
            if (it->second->first <= now)
            {
                args.invalidate();
            }
        }
        else //not found: probably removed by onReplace
            args.invalidate();
    }

    void onReplace(const void *, std::set<TKey> & elemsToRemove)
    {
        // Note: replace only informs the cache which elements
        // it would like to remove!
        // it does not remove them on its own!
        IndexIterator it = _keyIndex.begin();
        Timestamp now;
        while (it != _keyIndex.end() && it->first < now)
        {
            elemsToRemove.insert(it->second.first);
            ++it;
        }
    }

protected:
    Keys _keys; /// For faster replacement of keys, the iterator points to the _keyIndex map
    TimeIndex _keyIndex; /// Maps time to key value
};


} // namespace Poco


#endif // Foundation_UniqueAccessExpireStrategy_INCLUDED