hakmem/core/box/front_gate_box.c

// front_gate_box.c - Front Gate Box (SFC/SLL priority and helpers)
#include "front_gate_box.h"
#include "tiny_alloc_fast_sfc.inc.h"
#include "tls_sll_box.h"  // Box TLS-SLL API
#include "ptr_conversion_box.h"  // Box 3: Pointer conversions

// TLS SLL state (extern from hakmem_tiny.c)
extern __thread TinyTLSSLL g_tls_sll[TINY_NUM_CLASSES];
extern int g_tls_sll_enable;  // set at init via HAKMEM_TINY_TLS_SLL

// Front breakdown counters (extern from hakmem_tiny.c)
extern unsigned long long g_front_sfc_hit[];
extern unsigned long long g_front_sll_hit[];

// SFC feature flag (extern from hakmem_tiny_sfc.c)
extern int g_sfc_enabled;

int front_gate_try_pop(int class_idx, void** out_ptr) {
    if (!out_ptr) return 0;

    // Layer 0: SFC
    if (__builtin_expect(g_sfc_enabled, 1)) {
        void* base = sfc_alloc(class_idx);
        if (base != NULL) {
            g_front_sfc_hit[class_idx]++;
            /* BOX_BOUNDARY: Box 1 (SFC) → Box 3 → Box 4 (User) */
            /* sfc_alloc returns BASE, must convert to USER for caller */
            *out_ptr = PTR_BASE_TO_USER(base, class_idx);
            return 1;
        }
    }

    // Layer 1: TLS SLL
    if (__builtin_expect(g_tls_sll_enable, 1)) {
        void* base = NULL;
        if (tls_sll_pop(class_idx, &base)) {
            g_front_sll_hit[class_idx]++;
            /* BOX_BOUNDARY: Box 1 (TLS SLL) → Box 3 → Box 4 (User) */
            /* tls_sll_pop returns BASE, must convert to USER for caller */
            *out_ptr = PTR_BASE_TO_USER(base, class_idx);
            return 1;
        }
    }

    return 0;
}

// Cascade some of refilled blocks into SFC (one-way, safe)
void front_gate_after_refill(int class_idx, int refilled_count) {
    if (!g_sfc_enabled || refilled_count <= 0) return;

    int to_move = refilled_count / 2;
    if (to_move <= 0) return;

    while (to_move-- > 0 && g_tls_sll[class_idx].count > 0) {
        // SLL pop
        void* ptr = NULL;
        if (!tls_sll_pop(class_idx, &ptr)) break;

        // SFC push (capacity-guarded inside sfc_free_push)
        if (!sfc_free_push(class_idx, ptr)) {
            // If SFC refused (full), stop early to avoid spinning
            break;
        }
    }
}

void front_gate_push_tls(int class_idx, hak_base_ptr_t ptr) {
    // IMPORTANT: ptr is ALREADY a BASE pointer (callers from tiny_free_fast.inc.h
    // convert USER→BASE before calling tiny_alloc_fast_push)
    // Do NOT double-convert! Pass directly to TLS SLL which expects BASE.

    // Use Box TLS-SLL API (C7-safe; expects base pointer)
    if (!tls_sll_push(class_idx, ptr, UINT32_MAX)) {
        // C7 rejected or capacity exceeded - should not happen in front gate
        // but handle gracefully (silent discard)
        return;
    }
}