hakmem/core/box/tiny_route_box.h

// tiny_route_box.h - Box: Tiny Front Routing Policy
//
// Purpose:
//   Decide, per Tiny class, whether allocation should go through Tiny front
//   or directly to the Pool/backend. This keeps routing policy in a single,
//   cheap table lookup, without getenv() or complex logic in the hot path.
//
// Box Theory:
//   - Single Responsibility:
//       Only decides "Tiny vs Pool vs Tiny+Fallback" per class.
//   - Clear Boundary:
//       Front Gate / Alloc Gatekeeper calls tiny_route_get(class_idx) once.
//       Tiny Fast Path and Pool backend remain unchanged.
//   - Reversible / A/B:
//       Profiles are selected via HAKMEM_TINY_PROFILE ENV at init time.
//       Hot path is stable; routing can be tuned without touching fast code.

#ifndef TINY_ROUTE_BOX_H
#define TINY_ROUTE_BOX_H

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

// Routing policy per Tiny class.
typedef enum {
    ROUTE_TINY_ONLY  = 0,  // Tiny front only (no fallback; failure bubbles up)
    ROUTE_TINY_FIRST = 1,  // Try Tiny front, then fallback to Pool backend
    ROUTE_POOL_ONLY  = 2,  // Skip Tiny entirely, use Pool/backend only
} TinyRoutePolicy;

// Global routing table for Tiny classes (0..7).
// Initialized once from ENV: HAKMEM_TINY_PROFILE.
extern uint8_t g_tiny_route[8];

// Initialize routing table from ENV profile.
// Profiles:
//   "hot"          C0-C3=TINY_ONLY, C4-C6=TINY_FIRST, C7=POOL_ONLY
//   "conservative" 全クラス TINY_FIRST（デフォルト）
//   "off"          全クラス POOL_ONLY（Tiny 無効）
//   "full"         全クラス TINY_ONLY（microbench 用）
void tiny_route_init(void);

// Hot path helper: return routing policy for a given class.
// Uses simple array lookup; class_idx is masked to [0,7] defensively.
static inline TinyRoutePolicy tiny_route_get(int class_idx)
{
    TinyRoutePolicy p = (TinyRoutePolicy)g_tiny_route[class_idx & 7];
    #if HAKMEM_BUILD_RELEASE
    if ((class_idx & 7) == 7) {
        static int rel_route_logged = 0;
        if (!rel_route_logged) {
            const char* mode =
                (p == ROUTE_TINY_ONLY)  ? "TINY_ONLY"  :
                (p == ROUTE_TINY_FIRST) ? "TINY_FIRST" :
                (p == ROUTE_POOL_ONLY)  ? "POOL_ONLY"  : "UNKNOWN";
            fprintf(stderr, "[REL_C7_ROUTE] via tiny_route_get route=%s\n", mode);
            rel_route_logged = 1;
        }
    }
    #endif
    return p;
}

#endif // TINY_ROUTE_BOX_H