Juliet/AgentData/MemoryArena.md

Memory System Status & Migration Plan

Completed Work

Core Systems

• MemoryArena: Implemented linear allocator with alignment, markers, and reset support.
• Global Arenas:
  • ScratchArena (64MB): Transient per-frame memory.
  • EngineArena (256MB): Persistent engine memory (internal).
  • GameArena (512MB): Persistent game memory (exported to Game DLL).
• Helpers: Added ArenaPushType<T> and ArenaPushArray<T> with automatic zero-initialization.

Migrated Subsystems

• Display: Win32Window and Win32DisplayDevice now use EngineArena.
• Game Entities: Entity.h uses GameArena for entity allocation; manual free calls removed from game.cpp.
• Hot Reload: HotReload.cpp (persistent paths to EngineArena) and Win32HotReload.cpp (temp paths to ScratchArena).

Remaining Work

The following subsystems still use legacy malloc/calloc/realloc/free and need to be migrated.

IO System

• Files: Core/HAL/IO/IOStream.cpp, Core/HAL/IO/Win32/Win32IOStream.cpp
• Allocations: IOStream instance, data buffers, Win32IOStreamDataPayload.
• Challenge: Realloc is used for growing buffers.
• Strategy:
  • IOStream struct -> ScratchArena (if transient) or EngineArena.
  • Buffers: Evaluate if ArenaPush with large enough capacity is sufficient, or implement a growable buffer on top of arena (or use std::vector with custom allocator if absolutely needed, but prefer simple fixed max size if possible).

Graphics / Debug

• Files: Graphics/DebugDisplayRenderer.cpp
• Allocations: DepthTestedVertices, OverlayVertices.
• Strategy: Use EngineArena or a dedicated RenderArena if these are persistent. If per-frame, move to ScratchArena.

Shader Compiler

• Files: JulietShaderCompiler/ShaderCompiler.cpp
• Allocations: Argument arrays, file buffers.
• Strategy: Use ScratchArena for all compilation tasks as they are transient.

Filesystem

• Files: Core/HAL/Filesystem/Filesystem.cpp
• Allocations: CachedBasePath.
• Strategy: Migrate to EngineArena (persistent).