libtorrent-rasterbar-dev 1.1.1-1+b1 / usr / include / libtorrent / piece_picker.hpp

/*

Copyright (c) 2003-2016, Arvid Norberg
All rights reserved.

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modification, are permitted provided that the following conditions
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    * Redistributions of source code must retain the above copyright
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    * Redistributions in binary form must reproduce the above copyright
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      the documentation and/or other materials provided with the distribution.
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      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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*/
#ifndef TORRENT_PIECE_PICKER_HPP_INCLUDED
#define TORRENT_PIECE_PICKER_HPP_INCLUDED

// heavy weight reference counting invariant checks
//#define TORRENT_DEBUG_REFCOUNTS

#include "libtorrent/config.hpp"

#include "libtorrent/aux_/disable_warnings_push.hpp"

#include <algorithm>
#include <vector>
#include <bitset>
#include <utility>

#include <boost/static_assert.hpp>
#include <boost/cstdint.hpp>
#include <boost/tuple/tuple.hpp>

#ifdef TORRENT_DEBUG_REFCOUNTS
#include <set>
#endif

#if TORRENT_USE_ASSERTS
#include <set>
#endif

#include "libtorrent/aux_/disable_warnings_pop.hpp"

#include "libtorrent/peer_id.hpp"
#include "libtorrent/assert.hpp"
#include "libtorrent/time.hpp"

namespace libtorrent
{

	class torrent;
	class peer_connection;
	struct bitfield;
	struct counters;
	struct torrent_peer;

	struct TORRENT_EXTRA_EXPORT piece_block
	{
		static const piece_block invalid;

		piece_block() {}
		piece_block(int p_index, int b_index)
			: piece_index(p_index)
			, block_index(b_index)
		{
		}
		int piece_index;
		int block_index;

		bool operator<(piece_block const& b) const
		{
			if (piece_index < b.piece_index) return true;
			if (piece_index == b.piece_index) return block_index < b.block_index;
			return false;
		}

		bool operator==(piece_block const& b) const
		{ return piece_index == b.piece_index && block_index == b.block_index; }

		bool operator!=(piece_block const& b) const
		{ return piece_index != b.piece_index || block_index != b.block_index; }
	};

	class TORRENT_EXTRA_EXPORT piece_picker
	{
	public:

		enum
		{
			// the number of priority levels
			priority_levels = 8,
			// priority factor
			prio_factor = 3
		};

		struct block_info
		{
			block_info(): peer(0), num_peers(0), state(state_none) {}
			// the peer this block was requested or
			// downloaded from.
			torrent_peer* peer;
			// the number of peers that has this block in their
			// download or request queues
			unsigned num_peers:14;
			// the state of this block
			enum { state_none, state_requested, state_writing, state_finished };
			unsigned state:2;
#if TORRENT_USE_ASSERTS
			// to allow verifying the invariant of blocks belonging to the right piece
			int piece_index;
			std::set<torrent_peer*> peers;
#endif
		};

		enum options_t
		{
			// pick rarest first
			rarest_first = 1,
			// pick the most common first, or the last pieces if sequential
			reverse = 2,
			// only pick pieces exclusively requested from this peer
			on_parole = 4,
			// always pick partial pieces before any other piece
			prioritize_partials = 8,
			// pick pieces in sequential order
			sequential = 16,
			// treat pieces with priority 6 and below as filtered
			// to trigger end-game mode until all prio 7 pieces are
			// completed
			time_critical_mode = 32,
			// only expands pieces (when prefer contiguous blocks is set)
			// within properly aligned ranges, not the largest possible
			// range of pieces.
			align_expanded_pieces = 64
		};

		struct downloading_piece
		{
			downloading_piece() : index((std::numeric_limits<boost::uint32_t>::max)())
				, info_idx((std::numeric_limits<boost::uint16_t>::max)())
				, finished(0)
				, passed_hash_check(0)
				, writing(0)
				, locked(0)
				, requested(0)
				, outstanding_hash_check(0) {}

			bool operator<(downloading_piece const& rhs) const { return index < rhs.index; }

			// the index of the piece
			boost::uint32_t index;

			// info about each block in this piece. this is an index into the
			// m_block_info array, when multiplied by m_blocks_per_piece.
			// The m_blocks_per_piece following entries contain information about
			// all blocks in this piece.
			boost::uint16_t info_idx;

			// the number of blocks in the finished state
			boost::uint16_t finished:15;

			// set to true when the hash check job
			// returns with a valid hash for this piece.
			// we might not 'have' the piece yet though,
			// since it might not have been written to
			// disk. This is not set of locked is
			// set.
			boost::uint16_t passed_hash_check:1;

			// the number of blocks in the writing state
			boost::uint16_t writing:15;

			// when this is set, blocks from this piece may
			// not be picked. This is used when the hash check
			// fails or writing to the disk fails, while waiting
			// to synchronize the disk thread and clear out any
			// remaining state. Once this synchronization is
			// done, restore_piece() is called to clear the
			// locked flag.
			boost::uint16_t locked:1;

			// the number of blocks in the requested state
			boost::uint16_t requested:15;

			// set to true while there is an outstanding
			// hash check for this piece
			boost::uint16_t outstanding_hash_check:1;
		};

		piece_picker();

		void get_availability(std::vector<int>& avail) const;
		int get_availability(int piece) const;

		// increases the peer count for the given piece
		// (is used when a HAVE message is received)
		void inc_refcount(int index, const torrent_peer* peer);
		void dec_refcount(int index, const torrent_peer* peer);

		// increases the peer count for the given piece
		// (is used when a BITFIELD message is received)
		void inc_refcount(bitfield const& bitmask, const torrent_peer* peer);
		// decreases the peer count for the given piece
		// (used when a peer disconnects)
		void dec_refcount(bitfield const& bitmask, const torrent_peer* peer);

		// these will increase and decrease the peer count
		// of all pieces. They are used when seeds join
		// or leave the swarm.
		void inc_refcount_all(const torrent_peer* peer);
		void dec_refcount_all(const torrent_peer* peer);

		// This indicates that we just received this piece
		// it means that the refcounter will indicate that
		// we are not interested in this piece anymore
		// (i.e. we don't have to maintain a refcount)
		void we_have(int index);
		void we_dont_have(int index);

		// the lowest piece index we do not have
		int cursor() const { return m_cursor; }

		// one past the last piece we do not have.
		int reverse_cursor() const { return m_reverse_cursor; }

		// sets all pieces to dont-have
		void init(int blocks_per_piece, int blocks_in_last_piece, int total_num_pieces);
		int num_pieces() const { return int(m_piece_map.size()); }

		bool have_piece(int index) const;

		bool is_downloading(int index) const
		{
			TORRENT_ASSERT(index >= 0);
			TORRENT_ASSERT(index < int(m_piece_map.size()));

			piece_pos const& p = m_piece_map[index];
			return p.downloading();
		}

		// sets the priority of a piece.
		// returns true if the priority was changed from 0 to non-0
		// or vice versa
		bool set_piece_priority(int index, int prio);

		// returns the priority for the piece at 'index'
		int piece_priority(int index) const;

		// returns the current piece priorities for all pieces
		void piece_priorities(std::vector<int>& pieces) const;

		// ========== start deprecation ==============

		// fills the bitmask with 1's for pieces that are filtered
		void filtered_pieces(std::vector<bool>& mask) const;

		// ========== end deprecation ==============

		// pieces should be the vector that represents the pieces a
		// client has. It returns a list of all pieces that this client
		// has and that are interesting to download. It returns them in
		// priority order. It doesn't care about the download flag.
		// The user of this function must lookup if any piece is
		// marked as being downloaded. If the user of this function
		// decides to download a piece, it must mark it as being downloaded
		// itself, by using the mark_as_downloading() member function.
		// THIS IS DONE BY THE peer_connection::send_request() MEMBER FUNCTION!
		// The last argument is the torrent_peer pointer for the peer that
		// we'll download from.
		// prefer_contiguous_blocks indicates how many blocks we would like
		// to request contiguously. The blocks are not merged by the piece
		// picker, but may be coalesced later by the peer_connection.
		// this feature is used by web_peer_connection to request larger blocks
		// at a time to mitigate limited pipelining and lack of keep-alive
		// (i.e. higher overhead per request).
		boost::uint32_t pick_pieces(bitfield const& pieces
			, std::vector<piece_block>& interesting_blocks, int num_blocks
			, int prefer_contiguous_blocks, torrent_peer* peer
			, int options, std::vector<int> const& suggested_pieces
			, int num_peers
			, counters& pc
			) const;

		// picks blocks from each of the pieces in the piece_list
		// vector that is also in the piece bitmask. The blocks
		// are added to interesting_blocks, and busy blocks are
		// added to backup_blocks. num blocks is the number of
		// blocks to be picked. Blocks are not picked from pieces
		// that are being downloaded
		int add_blocks(int piece, bitfield const& pieces
			, std::vector<piece_block>& interesting_blocks
			, std::vector<piece_block>& backup_blocks
			, std::vector<piece_block>& backup_blocks2
			, int num_blocks, int prefer_contiguous_blocks
			, torrent_peer* peer, std::vector<int> const& ignore
			, int options) const;

		// picks blocks only from downloading pieces
		int add_blocks_downloading(downloading_piece const& dp
			, bitfield const& pieces
			, std::vector<piece_block>& interesting_blocks
			, std::vector<piece_block>& backup_blocks
			, std::vector<piece_block>& backup_blocks2
			, int num_blocks, int prefer_contiguous_blocks
			, torrent_peer* peer
			, int options) const;

		// clears the peer pointer in all downloading pieces with this
		// peer pointer
		void clear_peer(torrent_peer* peer);

#if TORRENT_USE_INVARIANT_CHECKS
		// this is an invariant check
		void check_peers();
#endif

//		int get_block_state(piece_block block) const;

		// returns true if any client is currently downloading this
		// piece-block, or if it's queued for downloading by some client
		// or if it already has been successfully downloaded
		bool is_requested(piece_block block) const;
		// returns true if the block has been downloaded
		bool is_downloaded(piece_block block) const;
		// returns true if the block has been downloaded and written to disk
		bool is_finished(piece_block block) const;

		// marks this piece-block as queued for downloading
		// options are flags from options_t.
		bool mark_as_downloading(piece_block block, torrent_peer* peer
			, int options = 0);

		// returns true if the block was marked as writing,
		// and false if the block is already finished or writing
		bool mark_as_writing(piece_block block, torrent_peer* peer);

		void mark_as_canceled(piece_block block, torrent_peer* peer);
		void mark_as_finished(piece_block block, torrent_peer* peer);
	
		// prevent blocks from being picked from this piece.
		// to unlock the piece, call restore_piece() on it
		void lock_piece(int piece);

		void write_failed(piece_block block);
		int num_peers(piece_block block) const;

		void piece_passed(int index);

//		void mark_as_checking(int index);
//		void mark_as_done_checking(int index);

		// returns information about the given piece
		void piece_info(int index, piece_picker::downloading_piece& st) const;

		struct piece_stats_t
		{
			int peer_count;
			int priority;
			bool have;
			bool downloading;
		};

		piece_stats_t piece_stats(int index) 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, torrent_peer* peer = 0);

		// returns true if all blocks in this piece are finished
		// or if we have the piece
		bool is_piece_finished(int index) const;

		// returns true if we have the piece or if the piece
		// has passed the hash check
		bool has_piece_passed(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;

		// return the peer pointers to all peers that participated in
		// this piece
		void get_downloaders(std::vector<torrent_peer*>& d, int index) const;

		std::vector<piece_picker::downloading_piece> get_download_queue() const;
		int get_download_queue_size() const;

		void get_download_queue_sizes(int* partial
			, int* full, int* finished, int* zero_prio) const;

		torrent_peer* 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; }

		// number of pieces whose hash has passed _and_ they have
		// been successfully flushed to disk. Including pieces we have
		// also filtered with priority 0 but have anyway.
		int num_have() const { return m_num_have; }

		// number of pieces whose hash has passed (but haven't necessarily
		// been flushed to disk yet)
		int num_passed() const { return m_num_passed; }

		// return true if we have all the pieces we wanted
		bool is_finished() const { return m_num_have - m_num_have_filtered == int(m_piece_map.size()) - m_num_filtered; }

		bool is_seeding() const { return m_num_have == int(m_piece_map.size()); }

		// the number of pieces we want and don't have
		int num_want_left() const { return num_pieces() - m_num_have - m_num_filtered + m_num_have_filtered; }

#if TORRENT_USE_INVARIANT_CHECKS
		void check_piece_state() const;
		// used in debug mode
		void verify_priority(int start, int end, int prio) const;
		void verify_pick(std::vector<piece_block> const& picked
			, bitfield const& bits) const;

		void check_peer_invariant(bitfield const& have, torrent_peer const* p) const;
		void check_invariant(const torrent* t = 0) const;
#endif

		// functor that compares indices on downloading_pieces
		struct has_index
		{
			has_index(int i): index(boost::uint32_t(i)) { TORRENT_ASSERT(i >= 0); }
			bool operator()(const downloading_piece& p) const
			{ return p.index == index; }
			boost::uint32_t index;
		};

		int blocks_in_last_piece() const
		{ return m_blocks_in_last_piece; }

		std::pair<int, int> distributed_copies() const;

		void set_num_pad_files(int n) { m_num_pad_files = n; }

		// return the array of block_info objects for a given downloading_piece.
		// this array has m_blocks_per_piece elements in it
		block_info* blocks_for_piece(downloading_piece const& dp);
		block_info const* blocks_for_piece(downloading_piece const& dp) const;

	private:

		friend struct piece_pos;

		boost::tuple<bool, bool, int, int> requested_from(
			piece_picker::downloading_piece const& p
			, int num_blocks_in_piece, torrent_peer* peer) const;

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

		// only defined when TORRENT_PICKER_LOG is defined, used for debugging
		// unit tests
		void print_pieces() const;

		struct piece_pos
		{
			piece_pos() {}
			piece_pos(int peer_count_, int index_)
				: peer_count(unsigned(peer_count_))
				, download_state(piece_pos::piece_open)
				, piece_priority(4)
				, index(unsigned(index_))
			{
				TORRENT_ASSERT(peer_count_ >= 0);
				TORRENT_ASSERT(index_ >= 0);
			}

			// download_state of this piece.
			enum state_t
			{
				// the piece is partially downloaded or requested
				piece_downloading,
				// partial pieces where all blocks in the piece have been requested
				piece_full,
				// partial pieces where all blocks in the piece have been received
				// and are either finished or writing
				piece_finished,
				// partial pieces whose priority is 0
				piece_zero_prio,

				// the states up to this point indicate the piece is being
				// downloaded (or at least has a partially downloaded piece
				// in one of the m_downloads buckets).
				num_download_categories,

				// the piece is open to be picked
				piece_open = num_download_categories,

				// this is not a new download category/download list bucket.
				// it still goes into the piece_downloading bucket. However,
				// it indicates that this piece only has outstanding requests
				// from reverse peers. This is to de-prioritize it somewhat
				piece_downloading_reverse,
				piece_full_reverse
			};

			// returns one of the valid download categories of state_t or
			// piece_open if this piece is not being downloaded
			int download_queue() const
			{
				if (download_state == piece_downloading_reverse)
					return piece_downloading;
				if (download_state == piece_full_reverse)
					return piece_full;
				return download_state;
			}

			bool reverse() const
			{
				return download_state == piece_downloading_reverse
					|| download_state == piece_full_reverse;
			}

			void unreverse()
			{
				switch (download_state)
				{
					case piece_downloading_reverse:
						download_state = piece_downloading;
						break;
					case piece_full_reverse:
						download_state = piece_full;
						break;
				}
			}

			void make_reverse()
			{
				switch (download_state)
				{
					case piece_downloading:
						download_state = piece_downloading_reverse;
						break;
					case piece_full:
						download_state = piece_full_reverse;
						break;
				}
			}

			// the number of peers that has this piece
			// (availability)
#ifdef TORRENT_OPTIMIZE_MEMORY_USAGE
			boost::uint32_t peer_count : 9;
#else
			boost::uint32_t peer_count : 16;
#endif

			// one of the enums from state_t. This indicates whether this piece
			// is currently being downloaded or not, and what state it's in if
			// it is. Specifically, as an optimization, pieces that have all blocks
			// requested from them are separated out into separate lists to make
			// lookups quicker. The main oddity is that whether a downloading piece
			// has only been requested from peers that are reverse, that's
			// recorded as piece_downloading_reverse, which really means the same
			// as piece_downloading, it just saves space to also indicate that it
			// has a bit lower priority. The reverse bit is only relevant if the
			// state is piece_downloading.
			boost::uint32_t download_state : 3;

			// TODO: 2 having 8 priority levels is probably excessive. It should
			// probably be changed to 3 levels + dont-download

			// is 0 if the piece is filtered (not to be downloaded)
			// 1 is low priority
			// 2 is low priority
			// 3 is mid priority
			// 4 is default priority
			// 5 is mid priority
			// 6 is high priority
			// 7 is high priority
			boost::uint32_t piece_priority : 3;

			// index in to the piece_info vector
#ifdef TORRENT_OPTIMIZE_MEMORY_USAGE
			boost::uint32_t index : 17;
#else
			boost::uint32_t index;
#endif

#ifdef TORRENT_DEBUG_REFCOUNTS
			// all the peers that have this piece
			std::set<const torrent_peer*> have_peers;
#endif

			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.
#ifdef TORRENT_OPTIMIZE_MEMORY_USAGE
				we_have_index = 0x3ffff,
#else
				we_have_index = 0xffffffff,
#endif
				// the priority value that means the piece is filtered
				filter_priority = 0,
				// the max number the peer count can hold
#ifdef TORRENT_OPTIMIZE_MEMORY_USAGE
				max_peer_count = 0x1ff
#else
				max_peer_count = 0xffff
#endif
			};

			bool have() const { return index == we_have_index; }
			void set_have() { index = we_have_index; TORRENT_ASSERT(have()); }
			void set_not_have() { index = 0; TORRENT_ASSERT(!have()); }
			bool downloading() const { return download_state != piece_open; }

			bool filtered() const { return piece_priority == filter_priority; }

			// this function returns the effective priority of the piece. It's
			// actually the sort order of this piece compared to other pieces. A
			// lower index means it will be picked before a piece with a higher
			// index.
			// The availability of the piece (the number of peers that have this
			// piece) is fundamentally controlling the priority. It's multiplied
			// by 3 to form 3 levels of priority for each availability.
			//
			//  downloading pieces (not reverse)
			//   |   open pieces (not downloading)
			//   |   |   downloading pieces (reverse peers)
			//   |   |   |
			// +---+---+---+
			// | 0 | 1 | 2 |
			// +---+---+---+
			// this '3' is called prio_factor
			//
			// the manually set priority takes precedence over the availability
			// by multiplying availability by priority.

			int priority(piece_picker const* picker) const
			{
				// filtered pieces (prio = 0), pieces we have or pieces with
				// availability = 0 should not be present in the piece list
				// returning -1 indicates that they shouldn't.
				if (filtered() || have() || peer_count + picker->m_seeds == 0
					|| download_state == piece_full
					|| download_state == piece_finished)
					return -1;

				TORRENT_ASSERT(piece_priority > 0);

				// this is to keep downloading pieces at higher priority than
				// pieces that are not being downloaded, and to make reverse
				// downloading pieces to be lower priority
				int adjustment = -2;
				if (reverse()) adjustment = -1;
				else if (download_state != piece_open) adjustment = -3;

				// the + 1 here is because peer_count count be 0, it m_seeds
				// is > 0. We don't actually care about seeds (except for the
				// first one) since the order of the pieces is unaffected.
				int availability = int(peer_count) + 1;
				TORRENT_ASSERT(availability > 0);
				TORRENT_ASSERT(int(priority_levels - piece_priority) > 0);

				return availability * int(priority_levels - piece_priority)
					* prio_factor + adjustment;
			}

			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; }
		};

#ifndef TORRENT_DEBUG_REFCOUNTS
#ifdef TORRENT_OPTIMIZE_MEMORY_USAGE
		BOOST_STATIC_ASSERT(sizeof(piece_pos) == sizeof(char) * 4);
#else
		BOOST_STATIC_ASSERT(sizeof(piece_pos) == sizeof(char) * 8);
#endif
#endif

		bool partial_compare_rarest_first(downloading_piece const* lhs
		, downloading_piece const* rhs) const;

		void break_one_seed();

		void update_pieces() const;

		// fills in the range [start, end) of pieces in
		// m_pieces that have priority 'prio'
		void priority_range(int prio, int* start, int* end);

		// adds the piece 'index' to m_pieces
		void add(int index);
		// removes the piece with the given priority and the
		// elem_index in the m_pieces vector
		void remove(int priority, int elem_index);
		// updates the position of the piece with the given
		// priority and the elem_index in the m_pieces vector
		void update(int priority, int elem_index);
		// shuffles the given piece inside it's priority range
		void shuffle(int priority, int elem_index);

		typedef std::vector<downloading_piece>::iterator dlpiece_iter;
		dlpiece_iter add_download_piece(int index);
		void erase_download_piece(dlpiece_iter i);

		std::vector<downloading_piece>::const_iterator find_dl_piece(int queue, int index) const;
		std::vector<downloading_piece>::iterator find_dl_piece(int queue, int index);

		// returns an iterator to the downloading piece, whichever
		// download list it may live in now
		std::vector<downloading_piece>::iterator update_piece_state(
			std::vector<downloading_piece>::iterator dp);

	private:

		// the following vectors are mutable because they sometimes may
		// be updated lazily, triggered by const functions

		// 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
		// TODO: should this be allocated lazily?
		mutable std::vector<piece_pos> m_piece_map;

		// the number of seeds. These are not added to
		// the availability counters of the pieces
		int m_seeds;

		// the number of pieces that have passed the hash check
		int m_num_passed;

		// this vector contains all piece indices that are pickable
		// sorted by priority. Pieces are in random random order
		// among pieces with the same priority
		mutable std::vector<int> m_pieces;

		// these are indices to the priority boundries inside
		// the m_pieces vector. priority 0 always start at
		// 0, priority 1 starts at m_priority_boundries[0] etc.
		mutable std::vector<int> m_priority_boundries;

		// each piece that's currently being downloaded has an entry in this list
		// with block allocations. i.e. it says which parts of the piece that is
		// being downloaded. This list is ordered by piece index to make lookups
		// efficient there are as many buckets as there are piece states. See
		// piece_pos::state_t. The only download state that does not have a
		// corresponding downloading_piece vector is piece_open and
		// piece_downloading_reverse (the latter uses the same as
		// piece_downloading).
		std::vector<downloading_piece> m_downloads[piece_pos::num_download_categories];

		// this holds the information of the blocks in partially downloaded
		// pieces. the downloading_piece::info index point into this vector for
		// its storage
		std::vector<block_info> m_block_info;

		// these are block ranges in m_block_info that are free. The numbers
		// in here, when multiplied by m_blocks_per_piece is the index to the
		// first block in the range that's free to use by a new downloading_piece.
		// this is a free-list.
		std::vector<boost::uint16_t> m_free_block_infos;

		boost::uint16_t m_blocks_per_piece;
		boost::uint16_t 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;

		// we have all pieces in the range [0, m_cursor)
		// m_cursor is the first piece we don't have
		int m_cursor;

		// we have all pieces in the range [m_reverse_cursor, end)
		// m_reverse_cursor is the first piece where we also have
		// all the subsequent pieces
		int m_reverse_cursor;

		// the number of pieces we have (i.e. passed + flushed).
		// This includes pieces that we have filtered but still have
		int m_num_have;

		// this is the number of partial download pieces
		// that may be caused by pad files. We raise the limit
		// of number of partial pieces by this amount, to not
		// prioritize pieces that intersect pad files for no
		// apparent reason
		int m_num_pad_files;

		// if this is set to true, it means update_pieces()
		// has to be called before accessing m_pieces.
		mutable bool m_dirty;
	public:

#ifdef TORRENT_OPTIMIZE_MEMORY_USAGE
		enum { max_pieces = piece_pos::we_have_index - 1 };
#else
		enum { max_pieces = INT_MAX - 1 };
#endif

	};
}

#endif // TORRENT_PIECE_PICKER_HPP_INCLUDED