example6_11.cpp

 //线程安全查找表
 template <typename Key,typename Value,typename Hash=std::hash<Key> >
class threadsafe_lookup_table
{
private:
	class bucket_type
	{
	private:
		typedef std::pair<Key,Value> bucket_value;
		typedef std::list<bucket_value> bucket_data;
		typedef typename bucket_data::iterator bucket_iterator;

		bucket_data data;
		mutable boost::shared_mutex mutex;

		bucket_iterator find_entry_for(Key const& key) const
		{
			return std::find_if(data.begin(),data.end()
				,[&](bucket_value const& item){return item.first==key;});
		}
	public:
		Value value_for(Key const& key,Value const& default_value) const
		{
			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 add_or_update_mapping(Key const& key,Value const& value)
		{
			std::unique_lock<boost::shared_mutex> lock(mutex);
			bucket_iterator const found_entry=find_entry_for(key);
			if(found_entry==data.end())
			{
				data.push_back(bucket_value(key,value));
			}
			else
			{
				found_entry->second=value;
			}
		}

		void remove_mapping(Key const& key)
		{
			std::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);
			}
		}
	};

	std::vector<std::unique_ptr<bucket_type> > buckets;
	Hash hasher;

	bucket_type& get_bucket(Key const& key) const
	{
		std::size_t const bucket_index=hasher(key)%buckets.size();
		return *buckets[bucket_index];
	}
public:
	typedef Key key_type;
	typedef Value mapped_type;
	typedef Hash hash_type;

	threadsafe_lookup_table(unsigned num_buckets=19,Hash const& hasher_=Hash()):
		buckets(num_buckets),hasher(hasher_)
	{
		for(unsigned i=0;i<num_buckets;++i)
		{
			buckets[i].reset(new bucket_type);
		}
	}

	threadsafe_lookup_table(threadsafe_lookup_table const& other)=delete;
	threadsafe_lookup_table& operator=(threadsafe_lookup_table const& other)=delete;

	Value value_for(Key const& key,Value const& default_value=Value()) const
	{
		return get_bucket(key).value_for(key,default_value);
	}

	void add_or_update_mapping(Key const& key,Value const& value)
	{
		get_bucket(key).add_or_update_mapping(key,value);
	}

	void remove_mapping(Key const& key)
	{
		get_bucket(key).remove_mapping(key);
	}
};