diff --git a/doc/store_research.md b/doc/store_research.md deleted file mode 100644 index fa1fa5b..0000000 --- a/doc/store_research.md +++ /dev/null @@ -1,462 +0,0 @@ -# Store Crate: Deep Research & Performance Analysis - -This document covers the Rust `trictrac-store` crate that backs the OpenSpiel C++ game. -It traces the full data-flow from a C++ `get_legal_actions()` call down to individual -board operations, documents design decisions, and identifies performance bottlenecks -relevant to MCTS training throughput. - ---- - -## 1. Module Map - -| File | Responsibility | -|---|---| -| `board.rs` | `Board` (`[i8;24]`), `CheckerMove`, low-level move primitives | -| `dice.rs` | `Dice` (two `u8` values), `DiceRoller` | -| `player.rs` | `Color`, `Player` (score / holes / bredouille flags) | -| `game.rs` | `GameState` (the full game state machine + serialisation) | -| `game_rules_moves.rs` | `MoveRules` — legal move generation and validation | -| `game_rules_points.rs` | `PointsRules` — jan (scoring) computation | -| `training_common.rs` | Action encoding/decoding (`TrictracAction`, 514-element space) | -| `cxxengine.rs` | FFI bridge (cxx.rs) — the sole entry point from C++ | - ---- - -## 2. Data Model - -### 2.1 Board - -``` -positions: [i8; 24] // index i → field i+1 (fields are 1-indexed) -positive → white checkers -negative → black checkers -0 → empty -``` - -Fields 1–6 = player 1's home quarter ("petit jan"), 7–12 = big jan, 13–18 = opponent -big jan, 19–24 = opponent home quarter. -Field 12 = White rest corner, field 13 = Black rest corner. - -Mirror (for Black's perspective): negate every element and reverse the array. - -### 2.2 CheckerMove - -``` -CheckerMove { from: Field, to: Field } -from ∈ [1,24], to ∈ [0,24] (to==0 means bear off) -(0,0) = EMPTY_MOVE (no-op, used when a player cannot move one die) -``` - -### 2.3 Action Space (training_common.rs) - -514 discrete actions: - -| Index | Meaning | -|---|---| -| 0 | `Roll` — trigger a dice roll | -| 1 | `Go` — take the hole and reset (instead of holding) | -| 2–257 | `Move` with `dice_order=true` (die1 first): `2 + checker1*16 + checker2` | -| 258–513 | `Move` with `dice_order=false` (die2 first): `258 + checker1*16 + checker2` | - -`checker1` and `checker2` are 1-indexed ordinal positions of checkers from the -starting field (not the field index). This avoids a per-position bijection and keeps -the space fixed-size regardless of where checkers are. - -### 2.4 GameState - -Key fields that affect performance: - -```rust -pub struct GameState { - pub board: Board, // 24 bytes - pub active_player_id: u64, // 1 or 2 - pub players: HashMap, // 2 entries - pub history: Vec, // grows unboundedly - pub dice: Dice, // 2 bytes - pub dice_points: (u8, u8), - pub dice_moves: (CheckerMove, CheckerMove), - pub dice_jans: PossibleJans, // HashMap> - pub turn_stage: TurnStage, - pub stage: Stage, - ... -} -``` - -`history` is the largest field and grows ~3–4 entries per turn. -A 200-turn game holds ~600 `GameEvent` values. - ---- - -## 3. Call Chain: get_legal_actions (C++ → Rust) - -``` -C++ LegalActions() - └─ engine_->get_legal_actions(player_idx) [cxxengine.rs] - └─ get_valid_action_indices(&game_state or &mirrored) - └─ get_valid_actions(state) [training_common.rs] - └─ MoveRules::get_possible_moves_sequences(true, []) - ├─ get_possible_moves_sequences_by_dices(dice_max, dice_min, ...) - │ ├─ board.get_possible_moves(dice1) [loop over fields] - │ └─ for each first_move: - │ ├─ board.clone() [24-byte copy] - │ ├─ board2.get_possible_moves(dice2) - │ └─ for each second_move: - │ ├─ check_corner_rules() - │ ├─ check_opponent_can_fill_quarter_rule() - │ ├─ check_exit_rules() [may recurse!] - │ └─ check_must_fill_quarter_rule() [recurses!] - └─ get_possible_moves_sequences_by_dices(dice_min, dice_max, ...) - [same structure as above] -``` - -Then for each valid `(CheckerMove, CheckerMove)` pair, `checker_moves_to_trictrac_action()` -maps it back to a `TrictracAction`: - -``` -checker_moves_to_trictrac_action(move1, move2, color, state) - └─ white_checker_moves_to_trictrac_action(...) - ├─ board.get_field_checker(White, from1) [O(24) scan] - ├─ board.clone() - ├─ board.move_checker(White, move1) [board mutation] - └─ board.get_field_checker(White, from2) [O(24) scan] -``` - -For **player 2**, an extra `GameState::mirror()` is called before all of this, -cloning the full state including history. - ---- - -## 4. Move Generation Deep Dive - -### 4.1 get_possible_moves_sequences - -```rust -pub fn get_possible_moves_sequences( - &self, - with_excedents: bool, - ignored_rules: Vec, -) -> Vec<(CheckerMove, CheckerMove)> { - // called TWICE, once per dice order (max-first, then min-first) - let mut seqs = self.get_possible_moves_sequences_by_dices(dice_max, dice_min, ...); - let mut seqs2 = self.get_possible_moves_sequences_by_dices(dice_min, dice_max, ...); - seqs.append(&mut seqs2); - // deduplication via HashSet -} -``` - -The function is **correct but called recursively** through rule validation: - -- `check_must_fill_quarter_rule()` calls `get_quarter_filling_moves_sequences()` -- `get_quarter_filling_moves_sequences()` calls `get_possible_moves_sequences(true, [Exit, MustFillQuarter])` -- This inner call's `check_must_fill_quarter_rule()` does **not** recurse further (because `MustFillQuarter` is in ignored_rules) - -So there are at most **2 levels of recursion**, but the second level is invoked once per -candidate move pair at the outer level. If there are N first-moves × M second-moves, -`get_quarter_filling_moves_sequences()` is called N×M times and each call triggers a -full second-level move generation pass. - -### 4.2 get_possible_moves_sequences_by_dices - -```rust -for first_move in board.get_possible_moves(dice1, ...) { - let mut board2 = self.board.clone(); // ← clone per first move - board2.move_checker(color, first_move); - for second_move in board2.get_possible_moves(dice2, ...) { - // 4 rule checks, each potentially expensive - if all_pass { - moves_seqs.push((first_move, second_move)); - } - } - if !has_second { - // also push (first_move, EMPTY_MOVE) after same 4 checks - } -} -``` - -**Board clones**: one per first-move candidate. With 15 checkers on 24 fields, a -typical position has 5–15 valid first moves → 5–15 board clones per call. - -### 4.3 check_must_fill_quarter_rule - -```rust -fn check_must_fill_quarter_rule(&self, moves) -> Result<(), MoveError> { - let filling_moves_sequences = self.get_quarter_filling_moves_sequences(); - if !filling_moves_sequences.contains(moves) && !filling_moves_sequences.is_empty() { - return Err(MoveError::MustFillQuarter); - } - Ok(()) -} -``` - -`get_quarter_filling_moves_sequences()` runs a full pass of move generation and -applies both checker moves to a board clone for each candidate: - -```rust -pub fn get_quarter_filling_moves_sequences(&self) -> Vec<(CheckerMove, CheckerMove)> { - for moves in self.get_possible_moves_sequences(true, [Exit, MustFillQuarter]) { - let mut board = self.board.clone(); // ← clone per candidate - board.move_checker(color, moves.0).unwrap(); - board.move_checker(color, moves.1).unwrap(); - if board.any_quarter_filled(Color::White) { - moves_seqs.push(moves); - } - } - moves_seqs -} -``` - -If quarter-filling is not relevant to the current position (the common case early in -the game), this entire function still runs a full move generation pass before returning -an empty vec. - -### 4.4 check_exit_rules - -```rust -fn check_exit_rules(&self, moves) -> Result<(), MoveError> { - if !moves.0.is_exit() && !moves.1.is_exit() { return Ok(()); } - if self.has_checkers_outside_last_quarter() { return Err(...); } - let non_excedent_seqs = self.get_possible_moves_sequences(false, [Exit]); // ← full pass - if non_excedent_seqs.contains(moves) { return Ok(()); } - if !non_excedent_seqs.is_empty() { return Err(ExitByEffectPossible); } - // check farthest checker rule ... - Ok(()) -} -``` - -Called per candidate move pair during the inner loop. Triggers another full -`get_possible_moves_sequences(false, [Exit])` pass whenever a move involves bearing off. - ---- - -## 5. Jan (Points) Computation - -### 5.1 get_jans (game_rules_points.rs) - -Called once per dice roll via `game.rs: consume(RollResult)`. Not on the MCTS hot path -(MCTS does not need to compute points, only moves). However it is called during -`get_possible_moves_sequences()` indirectly via `get_scoring_quarter_filling_moves_sequences()`. - -`PossibleJans = HashMap>` — with only 13 possible -enum keys this is overkill. A fixed-size array would be faster. - -`PossibleJansMethods::push()` uses `ways.contains(&cmoves)` — O(n) linear search on -the existing moves list to avoid duplicates. For small lists this is fine, but it can -be called dozens of times per position. - -`PossibleJansMethods::merge()` for `TrueHitBigJan`/`TrueHitSmallJan` does two O(n) -scans per entry (one `contains`, one `retain`). - ---- - -## 6. State Encoding - -### 6.1 to_vec() — neural-network input (36 i8 values) - -``` -[0..23] board positions (i8, negative = black) -[24] active player color (0=white, 1=black) -[25] turn stage (u8 cast to i8) -[26] dice.values.0 -[27] dice.values.1 -[28..31] white player: points, holes, can_bredouille, can_big_bredouille -[32..35] black player: same -``` - -Simple, allocation-heavy (returns `Vec`). For the MCTS hot path, returning a -`[i8; 36]` stack array would avoid the heap allocation entirely. - -### 6.2 GameState::mirror() - -```rust -pub fn mirror(&self) -> GameState { - // Mirrors board (O(24)) - // Swaps and mirrors two player entries in a new HashMap - // Clones and mirrors the entire history Vec (O(history.len())) ← expensive - // Mirrors dice_moves (O(1)) - // Mirrors dice_jans (clone + HashMap iteration) - ... -} -``` - -`mirror()` is called on every `get_legal_actions()` invocation for player 2 (Black). -Cloning the history is **O(history.len())** and history grows through the entire game. - ---- - -## 7. Action Encoding/Decoding - -### 7.1 TrictracAction::to_event() — decode action index → GameEvent - -For `Move` actions, `to_event()`: -1. Reads `checker1` / `checker2` ordinal positions -2. Calls `board.get_checker_field(color, checker1)` — O(24) scan -3. Clones the board -4. Applies the first move on the clone -5. Calls `board.get_checker_field(color, checker2)` — O(24) scan on the clone -6. Adjusts for "prise par puissance" -7. Constructs the `GameEvent::Move` - -This is called once per `apply_action()` call from C++, so it is not as hot as legal -action generation. - -### 7.2 white_checker_moves_to_trictrac_action() — encode (CheckerMove, CheckerMove) → TrictracAction - -Called for **every valid move** during `get_valid_actions()`: -1. Computes `diff_move1` to identify which die was used first -2. Calls `board.get_field_checker(White, from1)` — O(24) scan -3. Clones the board -4. Calls `board.move_checker(White, move1)` — mutation on clone -5. Calls `board.get_field_checker(White, from2)` — O(24) scan on clone - -With 20 valid moves, this is 20 board clones + 40 O(24) scans per -`get_valid_actions()` call. - ---- - -## 8. Identified Performance Bottlenecks - -Ordered by estimated impact on MCTS training throughput: - -### 8.1 [HIGH] Recursive move generation in check_must_fill_quarter_rule - -**Problem**: `get_possible_moves_sequences()` is called O(F₁ × F₂) times where F₁ and F₂ are -the number of first- and second-move candidates. Each inner call runs a complete move -generation pass. - -**When it triggers**: Only when at least one valid move would fill/preserve a quarter -of the board. This is a common situation especially in mid/late game. - -**Fix direction**: Precompute `get_quarter_filling_moves_sequences()` once per -`get_possible_moves_sequences()` call and pass it in, instead of recomputing it for -each candidate pair. - -### 8.2 [HIGH] GameState::mirror() copies history - -**Problem**: `mirror()` clones + iterates `self.history` on every `get_legal_actions()` -call for Black. The history grows proportionally to game length and serves no purpose -for action generation. - -**Fix direction**: Either skip history in `mirror()` (pass an empty `Vec` for that -field) or refactor `cxxengine.rs` to mirror only the board and thread color perspective -through the functions that need it. - -### 8.3 [MEDIUM] Board clones in get_possible_moves_sequences_by_dices - -**Problem**: One `board.clone()` per first-move candidate (5–15 per call). Each clone -is 24 bytes, but the allocator round-trip costs more than the copy. - -**Fix direction**: Apply and undo moves on a single mutable board (move + undo pattern) -rather than cloning. Board mutation is O(1) and undoing is symmetric. - -### 8.4 [MEDIUM] Board clones in get_quarter_filling_moves_sequences - -**Problem**: One `board.clone()` per candidate move sequence, plus two `move_checker()` -calls (which can return Err — currently `.unwrap()`ed). These clones are nested inside -the already-expensive recursive path described in 8.1. - -**Fix direction**: Same move + undo pattern as 8.3. - -### 8.5 [MEDIUM] Board clones and O(24) scans in checker_moves_to_trictrac_action - -**Problem**: Called for every valid move in `get_valid_actions()`. With 20 valid moves, -this is 20 clones + 40 O(24) scans. - -**Fix direction**: Pass the checker ordinal index directly from `get_board_exit_farthest` -or store it alongside the CheckerMove when generating moves. This avoids re-scanning -to convert back. - -### 8.6 [MEDIUM] check_exit_rules triggers a full move generation pass - -**Problem**: Called for every candidate move pair that involves bearing off. Runs -`get_possible_moves_sequences(false, [Exit])` → another full move generation. - -**Fix direction**: Precompute non-excedant moves once if any move in the candidate set -involves bearing off, and pass the result in. - -### 8.7 [LOW] PossibleJans backed by HashMap with linear-search deduplication - -**Problem**: Only 13 `Jan` variants exist. A `HashMap` adds hashing overhead and -pointer indirection. `Vec::contains()` for deduplication is O(n). - -**Fix direction**: Use `[Option>; 13]` with `Jan as usize` index. For -deduplication use a `BTreeSet` or just sort + dedup (the lists are short). - -### 8.8 [LOW] to_vec() returns a heap-allocated Vec - -**Problem**: Called from C++ via `get_tensor()` on every MCTS rollout observation. - -**Fix direction**: Return `[i8; 36]` or write directly into a pre-allocated C++-owned -buffer (possible with cxx.rs via `Pin<&mut CxxVector>`). - -### 8.9 [LOW] get_color_fields() allocates a Vec on every call - -**Problem**: Called repeatedly in move generation (once per first-move enumeration, -once in is_quarter_fillable per field, etc.). - -**Fix direction**: Return a fixed-size `ArrayVec<(Field, i8), 24>` (using the -`arrayvec` crate) or add a small-vec optimisation. - -### 8.10 [LOW] unwrap() calls in hot paths (correctness concern) - -Currently `.unwrap()` in: -- `get_quarter_filling_moves_sequences()` line 529-530: `board.move_checker(...).unwrap()` -- Multiple places in `game_rules_points.rs` - -With `catch_unwind` wrapping at the FFI boundary these panics are now caught, but -they still abort the move and propagate an error to C++ rather than producing a clean -`SpielFatalError` message. These should be `?` with proper `Result` propagation or -`.expect()` with descriptive messages. - ---- - -## 9. Key Correctness Observations - -### 9.1 Game ends during chance action (fixed in alpha_zero.cc) - -`game.rs::consume(RollResult)` sets `stage = Stage::Ended` (line 795) when a player's -jan score grants their 13th hole on the dice roll itself. This makes a **chance action** -terminal. The OpenSpiel `PlayGame` loop in `alpha_zero.cc` did not check `IsTerminal()` -after chance actions — this was the root cause of the SIGSEGV crash. Fixed by adding: -```cpp -state->ApplyAction(action); // chance action -if (state->IsTerminal()) { trajectory.returns = state->Returns(); break; } -``` - -### 9.2 current_player_idx() panics on underflow - -```rust -fn current_player_idx(&self) -> u64 { - self.game_state.active_player_id - 1 // u64 underflow if id == 0 -} -``` - -`active_player_id` is always 1 or 2 during normal play (set by `BeginGame`), so this -is safe in practice. However it should be wrapped in `catch_unwind` or guarded by an -explicit check for robustness: -```rust -self.game_state.active_player_id.saturating_sub(1) -``` - -### 9.3 Mirror is always from White's perspective - -`MoveRules` and `PointsRules` always reason from White's point of view. For Black, the -caller must mirror the board beforehand. The comment at the top of `game_rules_moves.rs` -documents this. `cxxengine.rs` correctly mirrors the `GameState` for player 2 before -calling `get_valid_action_indices()`. - ---- - -## 10. Summary Table - -| Bottleneck | Location | Estimated Severity | Fix Complexity | -|---|---|---|---| -| Recursive `get_possible_moves_sequences` in `check_must_fill_quarter_rule` | `game_rules_moves.rs:272` | High | Medium | -| `GameState::mirror()` clones history | `game.rs:159` | High | Low | -| Board clones per first-move in `get_possible_moves_sequences_by_dices` | `game_rules_moves.rs:555` | Medium | Medium | -| Board clones in `get_quarter_filling_moves_sequences` | `game_rules_moves.rs:528` | Medium | Medium | -| `check_exit_rules` triggers full move generation | `game_rules_moves.rs:335` | Medium | Medium | -| `checker_moves_to_trictrac_action` clones per valid move | `training_common.rs:326` | Medium | Low–Medium | -| `PossibleJans` HashMap + linear dedup | `game_rules_points.rs:67` | Low | Low | -| `to_vec()` heap allocation | `game.rs:213` | Low | Low | -| `get_color_fields()` Vec allocation | `board.rs:405` | Low | Medium | -| `unwrap()` in hot paths | multiple | Correctness | Low |