462 lines
18 KiB
Markdown
462 lines
18 KiB
Markdown
# 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<u64, Player>, // 2 entries
|
||
pub history: Vec<GameEvent>, // grows unboundedly
|
||
pub dice: Dice, // 2 bytes
|
||
pub dice_points: (u8, u8),
|
||
pub dice_moves: (CheckerMove, CheckerMove),
|
||
pub dice_jans: PossibleJans, // HashMap<Jan, Vec<(CM,CM)>>
|
||
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<TricTracRule>,
|
||
) -> 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<Jan, Vec<(CheckerMove, CheckerMove)>>` — 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<i8>`). 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<SmallVec<...>>; 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<i8>>`).
|
||
|
||
### 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 |
|