transmission/libtransmission/peer-mgr-wishlist.cc

176 lines
5.0 KiB
C++

// This file Copyright © Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
#include <algorithm> // std::min, std::partial_sort
#include <cstddef>
#include <set>
#include <utility>
#include <vector>
#define LIBTRANSMISSION_PEER_MODULE
#include "libtransmission/transmission.h"
#include "libtransmission/crypto-utils.h" // for tr_salt_shaker
#include "libtransmission/peer-mgr-wishlist.h"
#include "libtransmission/utils.h"
namespace
{
using SaltType = tr_piece_index_t;
struct Candidate
{
tr_piece_index_t piece;
size_t n_blocks_missing;
tr_priority_t priority;
SaltType salt;
Candidate(tr_piece_index_t piece_in, size_t missing_in, tr_priority_t priority_in, SaltType salt_in)
: piece{ piece_in }
, n_blocks_missing{ missing_in }
, priority{ priority_in }
, salt{ salt_in }
{
}
[[nodiscard]] constexpr auto compare(Candidate const& that) const noexcept // <=>
{
// prefer pieces closer to completion
if (auto const val = tr_compare_3way(n_blocks_missing, that.n_blocks_missing); val != 0)
{
return val;
}
// prefer higher priority
if (auto const val = tr_compare_3way(priority, that.priority); val != 0)
{
return -val;
}
return tr_compare_3way(salt, that.salt);
}
bool operator<(Candidate const& that) const // less than
{
return compare(that) < 0;
}
};
std::vector<Candidate> getCandidates(Wishlist::Mediator const& mediator)
{
// count up the pieces that we still want
auto wanted_pieces = std::vector<std::pair<tr_piece_index_t, size_t>>{};
auto const n_pieces = mediator.countAllPieces();
wanted_pieces.reserve(n_pieces);
for (tr_piece_index_t i = 0; i < n_pieces; ++i)
{
if (!mediator.clientCanRequestPiece(i))
{
continue;
}
size_t const n_missing = mediator.countMissingBlocks(i);
if (n_missing == 0)
{
continue;
}
wanted_pieces.emplace_back(i, n_missing);
}
// transform them into candidates
auto salter = tr_salt_shaker<SaltType>{};
auto const n = std::size(wanted_pieces);
auto candidates = std::vector<Candidate>{};
auto const is_sequential = mediator.isSequentialDownload();
candidates.reserve(n);
for (size_t i = 0; i < n; ++i)
{
auto const [piece, n_missing] = wanted_pieces[i];
auto const salt = is_sequential ? piece : salter();
candidates.emplace_back(piece, n_missing, mediator.priority(piece), salt);
}
return candidates;
}
std::vector<tr_block_span_t> makeSpans(tr_block_index_t const* sorted_blocks, size_t n_blocks)
{
if (n_blocks == 0)
{
return {};
}
auto spans = std::vector<tr_block_span_t>{};
auto cur = tr_block_span_t{ sorted_blocks[0], sorted_blocks[0] + 1 };
for (size_t i = 1; i < n_blocks; ++i)
{
if (cur.end == sorted_blocks[i])
{
++cur.end;
}
else
{
spans.push_back(cur);
cur = tr_block_span_t{ sorted_blocks[i], sorted_blocks[i] + 1 };
}
}
spans.push_back(cur);
return spans;
}
} // namespace
std::vector<tr_block_span_t> Wishlist::next(size_t n_wanted_blocks)
{
if (n_wanted_blocks == 0)
{
return {};
}
auto candidates = getCandidates(mediator_);
// We usually won't need all the candidates to be sorted until endgame, so don't
// waste cycles sorting all of them here. partial sort is enough.
static auto constexpr MaxSortedPieces = size_t{ 30 };
auto const middle = std::min(std::size(candidates), MaxSortedPieces);
std::partial_sort(std::begin(candidates), std::begin(candidates) + middle, std::end(candidates));
auto blocks = std::set<tr_block_index_t>{};
for (auto const& candidate : candidates)
{
// do we have enough?
if (std::size(blocks) >= n_wanted_blocks)
{
break;
}
// walk the blocks in this piece
auto const [begin, end] = mediator_.blockSpan(candidate.piece);
for (tr_block_index_t block = begin; block < end && std::size(blocks) < n_wanted_blocks; ++block)
{
// don't request blocks we've already got
if (!mediator_.clientCanRequestBlock(block))
{
continue;
}
// don't request from too many peers
size_t const n_peers = mediator_.countActiveRequests(block);
if (size_t const max_peers = mediator_.isEndgame() ? 2 : 1; n_peers >= max_peers)
{
continue;
}
blocks.insert(block);
}
}
auto const blocks_v = std::vector<tr_block_index_t>{ std::begin(blocks), std::end(blocks) };
return makeSpans(std::data(blocks_v), std::size(blocks_v));
}