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

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


#ifndef Foundation_ExpireStrategy_INCLUDED
#define Foundation_ExpireStrategy_INCLUDED


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


namespace Poco
{


template <class TKey, class TValue>
class ExpireStrategy : public AbstractStrategy<TKey, TValue>
/// An ExpireStrategy implements time based expiration of cache entries
{
public:
    typedef std::multimap<Timestamp, TKey> TimeIndex;
    typedef typename TimeIndex::iterator IndexIterator;
    typedef typename TimeIndex::const_iterator ConstIndexIterator;
    typedef std::map<TKey, IndexIterator> Keys;
    typedef typename Keys::iterator Iterator;

public:
    ExpireStrategy(Timestamp::TimeDiff expireTimeInMilliSec) : _expireTime(expireTimeInMilliSec * 1000)
    /// Create an expire strategy. Note that the smallest allowed caching time is 25ms.
    /// Anything lower than that is not useful with current operating systems.
    {
        if (_expireTime < 25000)
            throw InvalidArgumentException("expireTime must be at least 25 ms");
    }

    ~ExpireStrategy() { }

    void onAdd(const void *, const KeyValueArgs<TKey, TValue> & args)
    {
        Timestamp now;
        typename TimeIndex::value_type tiValue(now, args.key());
        IndexIterator it = _keyIndex.insert(tiValue);
        typename Keys::value_type kValue(args.key(), it);
        std::pair<Iterator, bool> stat = _keys.insert(kValue);
        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 triggers no changes in an expire
    }

    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())
        {
            if (it->second->first.isElapsed(_expireTime))
            {
                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();
        while (it != _keyIndex.end() && it->first.isElapsed(_expireTime))
        {
            elemsToRemove.insert(it->second);
            ++it;
        }
    }

protected:
    Timestamp::TimeDiff _expireTime;
    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_ExpireStrategy_INCLUDED