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ChessEngine: Use reduced Board objects in MCTSTree

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Monte-Carlo methods are known to intensively create nodes and in our
case each leaf of the tree stores a board. However, for this use case,
we don't need a full board object that also contains game information.

This patch adds a `clone_cleared()` method that return a clone without
game information and uses it when constructing the tree.
It allows the ChessEngine much more possibility before getting out of
memory.
This commit is contained in:
Lucas CHOLLET 2022-08-14 15:00:52 +02:00 committed by Andreas Kling
parent 5f13a87ce7
commit 351fc0cce2
Notes: sideshowbarker 2024-07-17 08:03:33 +09:00 
Author: https://github.com/LucasChollet
Commit: https://github.com/SerenityOS/serenity/commit/351fc0cce2
Pull-request: https://github.com/SerenityOS/serenity/pull/14855
Reviewed-by: https://github.com/linusg
Reviewed-by: https://github.com/petelliott ✅
3 changed files with 15 additions and 4 deletions
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10
Userland/Libraries/LibChess/Chess.cpp
View File

@ -259,6 +259,16 @@ Board::Board()
set_piece(Square("h8"), { Color::Black, Type::Rook });
}
Board Board::clone_without_history() const
{
// Note: When used in the MCTSTree, the board doesn't need to have all information about previous states.
// It spares a huge amount of memory.
auto result = *this;
result.m_moves.clear();
result.m_previous_states.clear();
return result;
}
String Board::to_fen() const
{
StringBuilder builder;

1
Userland/Libraries/LibChess/Chess.h
View File

@ -117,6 +117,7 @@ struct Move {
class Board {
public:
Board();
Board clone_without_history() const;
Piece get_piece(Square const&) const;
Piece set_piece(Square const&, Piece const&);

8
Userland/Services/ChessEngine/MCTSTree.cpp
View File

@ -39,10 +39,10 @@ MCTSTree& MCTSTree::expand()
VERIFY(!expanded() || m_children.size() == 0);
if (!m_moves_generated) {
m_board->generate_moves([&](Chess::Move move) {
Chess::Board clone = *m_board;
clone.apply_move(move);
m_children.append(make<MCTSTree>(clone, this));
m_board->generate_moves([&](Chess::Move chess_move) {
auto clone = m_board->clone_without_history();
clone.apply_move(chess_move);
m_children.append(make<MCTSTree>(move(clone), this));
return IterationDecision::Continue;
});
m_moves_generated = true;