LockedLookupTable.hpp

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/***************************************************
 *       _   _            _                        *
 *      | | | |          (_)                       *
 *      | |_| | ___  _ __ _ _______  _ __          *
 *      |  _  |/ _ \| '__| |_  / _ \| '_  \        *
 *      | | | | (_) | |  | |/ / (_) | | | |        *
 *      \_| |_/\___/|_|  |_/___\___/|_| |_|        *
 ***************************************************
 * This file is part of Horizon (c).
 *
 * Copyright (c) 2019 Sagun K. (sagunxp@gmail.com).
 * Copyright (c) 2019 Horizon Dev Team.
 *
 * Base Author - Sagun K. (sagunxp@gmail.com)
 *
 * This library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this library.  If not, see <http://www.gnu.org/licenses/>.
 **************************************************/
 
#ifndef HORIZON_CORE_MULTITHREADING_LOCKEDLOOKUPTABLE_HPP
#define HORIZON_CORE_MULTITHREADING_LOCKEDLOOKUPTABLE_HPP
 
#include <iostream>
#include <string>
#include <boost/thread/shared_mutex.hpp>
#include <boost/thread.hpp>
#include <memory>
#include <list>
#include <vector>
 
 
template <typename Key, typename Value, typename Hash = std::hash<Key>>
class LockedLookupTable
{
    class bucket_type;
public:
    typedef Key key_type;
    typedef Value mapped_type;
    typedef Hash hash_type;
 
    LockedLookupTable(unsigned num_buckets = 19, const Hash &hasher_ = Hash())
    : _buckets(num_buckets), hasher(hasher_)
    {
        for (unsigned i = 0; i < num_buckets; ++i)
            _buckets[i].reset(new bucket_type);
    }
 
    LockedLookupTable(const LockedLookupTable &other) = delete;
    LockedLookupTable &operator=(const LockedLookupTable &other) = delete;
 
    Value const &operator[] (Key &k) { at(k); }
    
    Value at(Key const &key, Value const &default_value = Value()) const
    {
        return get_bucket(key).at(key, default_value);
    }
 
    void insert(const Key &key, const Value &value)
    {
        get_bucket(key).insert(key, value);
    }
 
    void erase(const Key &key)
    {
        get_bucket(key).erase(key);
    }
 
    std::map<Key, Value> get_map() const
    {
        std::map<Key, Value> res;
 
        for (unsigned i = 0; i < _buckets.size(); ++i) {
            boost::unique_lock<boost::shared_mutex> lock(_buckets[i]->_mutex);
            for (typename bucket_type::bucket_iterator it = _buckets[i]->data.begin();
                 it != _buckets[i]->data.end();
                 ++it) {
                res.insert(*it);
            }
        }
 
        return res;
    }
 
    int max_collisions() { return _buckets[0]->data.size() ? _buckets[0]->data.size() - 1 : 0; }
 
    std::size_t size()
    {
        std::size_t count = 0;
 
        for (unsigned i = 0; i < _buckets.size(); ++i) {
            boost::unique_lock<boost::shared_mutex> lock(_buckets[i]->_mutex);
            for (typename bucket_type::bucket_iterator it = _buckets[i]->data.begin();
                 it != _buckets[i]->data.end();
                 ++it) {
                count++;
            }
        }
 
        return count;
    }
 
    void clear()
    {
        for (unsigned i = 0; i < _buckets.size(); ++i) {
            boost::unique_lock<boost::shared_mutex> lock(_buckets[i]->_mutex);
            _buckets[i]->data.clear();
        }
    }
    
private:
    std::vector<std::unique_ptr<bucket_type>> _buckets;
    Hash hasher;
 
    bucket_type &get_bucket(Key const &key) const
    {
        const std::size_t bucket_index = hasher(key) % _buckets.size();
        return *_buckets[bucket_index];
    }
 
    class bucket_type
    {
        typedef std::pair<Key, Value> bucket_value;
        typedef std::vector<bucket_value> bucket_data;
 
    public:
        typedef typename bucket_data::iterator bucket_iterator;
 
        Value at(Key const &key, Value const &default_value)
        {
            boost::shared_lock<boost::shared_mutex> lock(_mutex);
            bucket_iterator const found_entry = find_entry_for(key);
            return (found_entry == data.end()) ? default_value : found_entry->second;
        }
 
        void insert(Key const &key, Value const &value)
        {
            boost::unique_lock<boost::shared_mutex> lock(_mutex);
            bucket_iterator found_entry = find_entry_for(key);
 
            if (found_entry != data.end())
                data.erase(found_entry);
 
            data.push_back(bucket_value(key, value));
        }
 
        void erase(Key const &key)
        {
            boost::unique_lock<boost::shared_mutex> lock(_mutex);
            bucket_iterator const found_entry = find_entry_for(key);
            if (found_entry != data.end())
                data.erase(found_entry);
        }
 
        bucket_data data;
        mutable boost::shared_mutex _mutex;
 
    private:
        bucket_iterator find_entry_for(Key const &key)
        {
            return std::find_if(data.begin(), data.end(),
                [&](bucket_value const &item)
                {
                    return item.first == key;
                });
        }
    };
};
 
#endif /* HORIZON_CORE_MULTITHREADING_LOCKEDLOOKUPTABLE_HPP */