hakmem/core/box/front_fastlane_stats_box.h

#ifndef HAK_FRONT_FASTLANE_STATS_BOX_H
#define HAK_FRONT_FASTLANE_STATS_BOX_H

// ============================================================================
// Phase 6: Front FastLane - Stats Box
// ============================================================================
//
// Purpose: Visibility into FastLane hit/fallback rates
//
// Counters (compile-out when HAKMEM_DEBUG_COUNTERS=0):
//
//   Malloc:
//     - malloc_total: Total try_malloc attempts
//     - malloc_hit: Successful FastLane alloc
//     - malloc_fallback_*: Fallback reasons (3-6 types)
//
//   Free:
//     - free_total: Total try_free attempts
//     - free_hit: Successful FastLane free
//     - free_fallback_*: Fallback reasons (3-6 types)
//
// Output (on exit, if HAKMEM_DEBUG_COUNTERS=1):
//   [FRONT_FASTLANE] malloc_total=N hit=N fb_*=N ... free_total=N hit=N fb_*=N ...
//
// Box Theory:
//   - L2: Stats layer (compile-out when counters disabled)
//   - Zero overhead: No-op macros when HAKMEM_DEBUG_COUNTERS=0
//
// ============================================================================

#include <stdatomic.h>
#include <stdint.h>
#include <stdio.h>

#if HAKMEM_DEBUG_COUNTERS

// Stats structure (global, thread-safe via atomics)
typedef struct {
    // Malloc stats
    _Atomic uint64_t malloc_total;          // Total try_malloc calls
    _Atomic uint64_t malloc_hit;            // Successful FastLane alloc
    _Atomic uint64_t malloc_fallback_stub;  // Stub: not implemented yet (Patch 2)
    _Atomic uint64_t malloc_fallback_size;  // Size out of Tiny range
    _Atomic uint64_t malloc_fallback_class; // Class calculation failed
    _Atomic uint64_t malloc_fallback_alloc; // Allocation failed (refill needed)
    _Atomic uint64_t malloc_fallback_other; // Other reasons

    // Free stats
    _Atomic uint64_t free_total;            // Total try_free calls
    _Atomic uint64_t free_hit;              // Successful FastLane free
    _Atomic uint64_t free_fallback_stub;    // Stub: not implemented yet (Patch 2)
    _Atomic uint64_t free_fallback_aligned; // Page-aligned pointer
    _Atomic uint64_t free_fallback_header;  // Invalid header magic
    _Atomic uint64_t free_fallback_class;   // Class out of bounds
    _Atomic uint64_t free_fallback_failure; // Free failed (cold path needed)
    _Atomic uint64_t free_fallback_other;   // Other reasons
} FrontFastLaneStats;

// Global stats instance
static FrontFastLaneStats g_front_fastlane_stats = {0};

// Increment macros (relaxed ordering - stats only)
// Phase 18 v2: BENCH_MINIMAL conditional (no-op when HAKMEM_BENCH_MINIMAL=1)
#if HAKMEM_BENCH_MINIMAL
#define FRONT_FASTLANE_STAT_INC(field) do { (void)0; } while(0)
#else
#define FRONT_FASTLANE_STAT_INC(field) \
    atomic_fetch_add_explicit(&g_front_fastlane_stats.field, 1, memory_order_relaxed)
#endif

// Dump stats on exit (call from wrapper destructor or main)
static void front_fastlane_stats_dump(void) {
    uint64_t m_total = atomic_load_explicit(&g_front_fastlane_stats.malloc_total, memory_order_relaxed);
    uint64_t f_total = atomic_load_explicit(&g_front_fastlane_stats.free_total, memory_order_relaxed);

    if (m_total == 0 && f_total == 0) return;  // No activity

    // Malloc stats
    uint64_t m_hit = atomic_load_explicit(&g_front_fastlane_stats.malloc_hit, memory_order_relaxed);
    uint64_t m_fb_stub = atomic_load_explicit(&g_front_fastlane_stats.malloc_fallback_stub, memory_order_relaxed);
    uint64_t m_fb_size = atomic_load_explicit(&g_front_fastlane_stats.malloc_fallback_size, memory_order_relaxed);
    uint64_t m_fb_class = atomic_load_explicit(&g_front_fastlane_stats.malloc_fallback_class, memory_order_relaxed);
    uint64_t m_fb_alloc = atomic_load_explicit(&g_front_fastlane_stats.malloc_fallback_alloc, memory_order_relaxed);
    uint64_t m_fb_other = atomic_load_explicit(&g_front_fastlane_stats.malloc_fallback_other, memory_order_relaxed);

    // Free stats
    uint64_t f_hit = atomic_load_explicit(&g_front_fastlane_stats.free_hit, memory_order_relaxed);
    uint64_t f_fb_stub = atomic_load_explicit(&g_front_fastlane_stats.free_fallback_stub, memory_order_relaxed);
    uint64_t f_fb_aligned = atomic_load_explicit(&g_front_fastlane_stats.free_fallback_aligned, memory_order_relaxed);
    uint64_t f_fb_header = atomic_load_explicit(&g_front_fastlane_stats.free_fallback_header, memory_order_relaxed);
    uint64_t f_fb_class = atomic_load_explicit(&g_front_fastlane_stats.free_fallback_class, memory_order_relaxed);
    uint64_t f_fb_failure = atomic_load_explicit(&g_front_fastlane_stats.free_fallback_failure, memory_order_relaxed);
    uint64_t f_fb_other = atomic_load_explicit(&g_front_fastlane_stats.free_fallback_other, memory_order_relaxed);

    fprintf(stderr, "[FRONT_FASTLANE] malloc_total=%lu hit=%lu fb_stub=%lu fb_size=%lu fb_class=%lu fb_alloc=%lu fb_other=%lu | "
                    "free_total=%lu hit=%lu fb_stub=%lu fb_aligned=%lu fb_header=%lu fb_class=%lu fb_failure=%lu fb_other=%lu\n",
            (unsigned long)m_total, (unsigned long)m_hit,
            (unsigned long)m_fb_stub, (unsigned long)m_fb_size, (unsigned long)m_fb_class,
            (unsigned long)m_fb_alloc, (unsigned long)m_fb_other,
            (unsigned long)f_total, (unsigned long)f_hit,
            (unsigned long)f_fb_stub, (unsigned long)f_fb_aligned, (unsigned long)f_fb_header,
            (unsigned long)f_fb_class, (unsigned long)f_fb_failure, (unsigned long)f_fb_other);
}

#else  // HAKMEM_DEBUG_COUNTERS == 0

// No-op macros (zero overhead)
#define FRONT_FASTLANE_STAT_INC(field) do {} while(0)

static inline void front_fastlane_stats_dump(void) {}

#endif  // HAKMEM_DEBUG_COUNTERS

#endif  // HAK_FRONT_FASTLANE_STATS_BOX_H