docs/plans/infinite_loop_analysis.md

Infinite Loop Analysis - Serialization and Actions

Overview

Analysis of infinite loop causes in the Loveca game engine, focusing on serialization and action generation code.

Key Findings

1. Infinite Loop Detection

• Location: alphazero/training/overnight_pure_zero.py:224
• Mechanism: Detected when moves_taken >= max_moves (default: 2000 steps)
• Output: Logs to alphazero/training/loops/trace_it{iteration}_g{game_num}_{reason}.json

2. Trace Analysis (trace_it51_g5_Loop.json)

• Reason: "Loop" (not "Turn" or "Terminal")
• Pattern Found:
  • Phase 10 (LiveResult) repeated with Action ID 11000 (Select Choice Index 0)
  • Actions 599-716 show repeated "Select Choice Index 0" on phase 10
  • This suggests a failure to progress past LiveResult phase

3. Key Files for Investigation

Action Generation

• engine_rust_src/src/core/logic/action_gen/response.rs
  • Handles Response phase interactions
  • Contains fallback logic: receiver.add_action(0) if no actions generated (line 19-21)
  • Checks choice_type for various interaction types

Phase Handlers

• engine_rust_src/src/core/logic/handlers.rs
  • RPS handling (lines 54-112)
  • handle_rps: Detects draws and resets (line 92-96)
  • handle_liveresult: Processes LiveResult selections

Serialization

• engine_rust_src/src/core/logic/state.rs

  • GameState derives Serialize, Deserialize (line 252)
  • CoreGameState (line 128) contains interaction_stack: Vec<PendingInteraction>

• engine_rust_src/src/core/logic/models.rs

  • PendingInteraction struct (line 121)
  • Contains actions: Vec<i32> field (line 137) - potential serialization issue if actions grow infinitely

4. Potential Infinite Loop Causes

A. LiveResult Phase Loop

• When live_result_selection_pending is true, auto_step breaks early (game.rs line 869-870)
• If the AI keeps selecting the same action (11000), it may not progress

B. RPS Draw Loop

• RPS draws restart RPS with rps_choices = [-1, -1]
• Could loop indefinitely if both players keep choosing same move

C. Interaction Stack Issues

• PendingInteraction.actions accumulates action history
• If deserialization doesn't clear this properly, could cause issues

5. Code Snippets

ResponseGenerator Fallback (response.rs:17-21)

if receiver.is_empty() {
    receiver.add_action(0);
}

Auto-Step Loop Safety (game.rs:828-885)

let mut loop_count = 0;
while loop_count < 40 {
    // Safety limit to prevent infinite auto-stepping
    loop_count += 1;
}

Recommendations

1. Investigate Phase 10/LiveResult: Why does the game get stuck repeatedly selecting Choice 0?
2. Check PendingInteraction.actions: Verify this field doesn't accumulate unbounded data
3. RPS Draw Handling: Add a maximum draw count to prevent infinite RPS loops
4. Logging Enhancement: Add more detailed state logging when loops are detected