piece_picker.hpp

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		bool is_finished(piece_block block) const;

		// marks this piece-block as queued for downloading
		bool mark_as_downloading(piece_block block, void* peer
			, piece_state_t s);
		void mark_as_writing(piece_block block, void* peer);
		void mark_as_finished(piece_block block, void* peer);
		int num_peers(piece_block block) const;

		// returns information about the given piece
		void piece_info(int index, piece_picker::downloading_piece& st) const;
		
		// if a piece had a hash-failure, it must be restored and
		// made available for redownloading
		void restore_piece(int index);

		// clears the given piece's download flag
		// this means that this piece-block can be picked again
		void abort_download(piece_block block);

		bool is_piece_finished(int index) const;

		// returns the number of blocks there is in the given piece
		int blocks_in_piece(int index) const;

		// the number of downloaded blocks that hasn't passed
		// the hash-check yet
		int unverified_blocks() const;

		void get_downloaders(std::vector<void*>& d, int index) const;

		std::vector<downloading_piece> const& get_download_queue() const
		{ return m_downloads; }

		void* get_downloader(piece_block block) const;

		// the number of filtered pieces we don't have
		int num_filtered() const { return m_num_filtered; }

		// the number of filtered pieces we already have
		int num_have_filtered() const { return m_num_have_filtered; }

#ifndef NDEBUG
		// used in debug mode
		void check_invariant(const torrent* t = 0) const;
		void verify_pick(std::vector<piece_block> const& picked
			, std::vector<bool> const& bitfield) const;
#endif

		// functor that compares indices on downloading_pieces
		struct has_index
		{
			has_index(int i): index(i) { TORRENT_ASSERT(i >= 0); }
			bool operator()(const downloading_piece& p) const
			{ return p.index == index; }
			int index;
		};

		int blocks_in_last_piece() const
		{ return m_blocks_in_last_piece; }

		float distributed_copies() const;

	private:

		bool can_pick(int piece, std::vector<bool> const& bitmask) const;
		std::pair<int, int> expand_piece(int piece, int whole_pieces
			, std::vector<bool> const& have) const;

		struct piece_pos
		{
			piece_pos() {}
			piece_pos(int peer_count_, int index_)
				: peer_count(peer_count_)
				, downloading(0)
				, piece_priority(1)
				, index(index_)
			{
				TORRENT_ASSERT(peer_count_ >= 0);
				TORRENT_ASSERT(index_ >= 0);
			}

			// the number of peers that has this piece
			// (availability)
			unsigned peer_count : 10;
			// is 1 if the piece is marked as being downloaded
			unsigned downloading : 1;
			// is 0 if the piece is filtered (not to be downloaded)
			// 1 is normal priority (default)
			// 2 is higher priority than pieces at the same availability level
			// 3 is same priority as partial pieces
			// 4 is higher priority than partial pieces
			// 5 and 6 same priority as availability 1 (ignores availability)
			// 7 is maximum priority (ignores availability)
			unsigned piece_priority : 3;
			// index in to the piece_info vector
			unsigned index : 18;

			enum
			{
				// index is set to this to indicate that we have the
				// piece. There is no entry for the piece in the
				// buckets if this is the case.
				we_have_index = 0x3ffff,
				// the priority value that means the piece is filtered
				filter_priority = 0,
				// the max number the peer count can hold
				max_peer_count = 0x3ff
			};
			
			bool have() const { return index == we_have_index; }
			void set_have() { index = we_have_index; TORRENT_ASSERT(have()); }
			
			bool filtered() const { return piece_priority == filter_priority; }
			void filtered(bool f) { piece_priority = f ? filter_priority : 0; }
			
			int priority(int limit) const
			{
				if (downloading || filtered() || have()) return 0;
				// pieces we are currently downloading have high priority
				int prio = peer_count * 2;
				// if the peer_count is 0 or 1, the priority cannot be higher
				if (prio <= 1) return prio;
				if (prio >= limit * 2) prio = limit * 2;
				// the different priority levels
				switch (piece_priority)
				{
					case 1: return prio;
					case 2: return prio - 1;
					case 3: return (std::max)(prio / 2, 1);
					case 4: return (std::max)(prio / 2 - 1, 1);
					case 5: return (std::max)(prio / 3, 1);
					case 6: return (std::max)(prio / 3 - 1, 1);
					case 7: return 1;
				}
				return prio;
			}

			bool operator!=(piece_pos p) const
			{ return index != p.index || peer_count != p.peer_count; }

			bool operator==(piece_pos p) const
			{ return index == p.index && peer_count == p.peer_count; }

		};

		BOOST_STATIC_ASSERT(sizeof(piece_pos) == sizeof(char) * 4);

		bool is_ordered(int priority) const
		{
			return priority >= m_sequenced_download_threshold * 2;
		}

		void add(int index);
		void move(int vec_index, int elem_index);
		void sort_piece(std::vector<downloading_piece>::iterator dp);

		downloading_piece& add_download_piece();
		void erase_download_piece(std::vector<downloading_piece>::iterator i);

		// this vector contains all pieces we don't have.
		// in the first entry (index 0) is a vector of all pieces
		// that no peer have, the vector at index 1 contains
		// all pieces that exactly one peer have, index 2 contains
		// all pieces exactly two peers have and so on.
		// this is not entirely true. The availibility of a piece
		// is adjusted depending on its priority. But the principle
		// is that the higher index, the lower priority a piece has.
		std::vector<std::vector<int> > m_piece_info;

		// this maps indices to number of peers that has this piece and
		// index into the m_piece_info vectors.
		// piece_pos::we_have_index means that we have the piece, so it
		// doesn't exist in the piece_info buckets
		// pieces with the filtered flag set doesn't have entries in
		// the m_piece_info buckets either
		std::vector<piece_pos> m_piece_map;

		// each piece that's currently being downloaded
		// has an entry in this list with block allocations.
		// i.e. it says wich parts of the piece that
		// is being downloaded
		std::vector<downloading_piece> m_downloads;

		// this holds the information of the
		// blocks in partially downloaded pieces.
		// the first m_blocks_per_piece entries
		// in the vector belongs to the first
		// entry in m_downloads, the second
		// m_blocks_per_piece entries to the
		// second entry in m_downloads and so on.
		std::vector<block_info> m_block_info;

		int m_blocks_per_piece;
		int m_blocks_in_last_piece;

		// the number of filtered pieces that we don't already
		// have. total_number_of_pieces - number_of_pieces_we_have
		// - num_filtered is supposed to the number of pieces
		// we still want to download
		int m_num_filtered;

		// the number of pieces we have that also are filtered
		int m_num_have_filtered;
		
		// the number of pieces we have
		int m_num_have;

		// the required popularity of a piece in order to download
		// it in sequence instead of random order.
		int m_sequenced_download_threshold;
#ifndef NDEBUG
		bool m_files_checked_called;
#endif
	};

	inline int piece_picker::blocks_in_piece(int index) const
	{
		TORRENT_ASSERT(index >= 0);
		TORRENT_ASSERT(index < (int)m_piece_map.size());
		if (index+1 == (int)m_piece_map.size())
			return m_blocks_in_last_piece;
		else
			return m_blocks_per_piece;
	}

}

#endif // TORRENT_PIECE_PICKER_HPP_INCLUDED