# Current Task: Phase 9-2 Refactoring (Complete) & Phase 10 Preparation

**Date**: 2025-12-01
**Status**: **COMPLETE** (Phase 9-2) / **PLANNING** (Phase 10)
**Goal**: Legacy Backend Removal, Shared Pool Unification, and Type Safety

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## Phase 9-2 Achievements (Completed)

1.  **Legacy Backend Removal & Unification (2025-12-01)**
    *   **Eliminated Fallback**: Removed `hak_tiny_alloc_superslab_backend_legacy` fallback. Shared Pool is now the sole backend (`hak_tiny_alloc_superslab_box` -> `hak_tiny_alloc_superslab_backend_shared`).
    *   **Soft Cap Removed**: Removed the artificial "Soft Cap" limit in Shared Pool Stage 3, allowing it to handle full workload load.
    *   **EMPTY Recycling**: Implemented `SLAB_TRY_RECYCLE` with atomic batch decrement of `meta->used` in `_ss_remote_drain_to_freelist_unsafe`. This ensures EMPTY slabs are immediately returned to the global pool.
    *   **Race Condition Fix**: Moved `remove_superslab_from_legacy_head(ss)` to the *start* of `shared_pool_release_slab` to prevent Legacy Backend from allocating from a slab being recycled. Added `total_active_blocks` check before freeing.
    *   **Performance**: **50.3 M ops/s** in WS8192 benchmark (vs 16.5 M baseline). OOM/Crash issues resolved.

2.  **Critical Fixes (Deadlock & OOM)**
    *   **Deadlock**: `shared_pool_acquire_slab` releases `alloc_lock` before `superslab_allocate`.
    *   **Is Empty Return**: `tiny_free_local_box` now returns `int is_empty` status to allow safe, race-free recycling by the caller.

3.  **Code Refactoring**
    *   Modularized `hakmem_shared_pool.c` into `acquire/release/internal` components.

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## Next Phase: Phase 10 - Type Safety & Hardening

### 1. Pointer Type Safety (Debug Only)
*   **Issue**: Occasional `[TLS_SLL_HDR_RESET]` warnings indicate confusion between `BasePtr` (header start) and `UserPtr` (payload start).
*   **Solution**: Implement "Phantom Type" checking macros enabled only in debug builds.
    *   Define `hak_base_ptr_t` and `hak_user_ptr_t` structs in debug.
    *   Define strict conversion macros (`hak_base_to_user`, `hak_user_to_base`).
    *   Apply incrementally to `tls_sll_box`, `free_local_box`, and `remote_free_box`.
    *   **Goal**: Catch pointer arithmetic errors at compile time in debug mode.

### 2. Header Protection Hardening
*   **Goal**: Reinforce header integrity checks in `tiny_free_local_box` and `tls_sll_pop` using the new type system.

### 3. Fast Path Optimization
*   **Goal**: Re-evaluate hot path performance (Stage 1 lock-free) after Phase 9-2 stabilization.

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## Current Status
*   **Build**: Passing (Clean build verified).
*   **Benchmarks**:
    *   WS8192: **50.3 M ops/s** (Shared Pool ONLY).
    *   Crash/OOM: Resolved.
*   **Pending**: Phase 10 implementation (Type Safety).