hakmem/core/box/mailbox_box.c

// mailbox_box.c - Publish Mailbox box (fully separated)
#include "mailbox_box.h"
#include "hakmem_tiny.h"
#include "tiny_debug_ring.h"
#include <stdatomic.h>
#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>

#ifndef MAILBOX_SHARDS
#define MAILBOX_SHARDS 64
#endif

// Shared state (per class)
static _Atomic(uintptr_t) g_pub_mailbox_entries[TINY_NUM_CLASSES][MAILBOX_SHARDS];
static _Atomic(uint32_t)  g_pub_mailbox_claimed[TINY_NUM_CLASSES][MAILBOX_SHARDS];
static _Atomic(uint32_t)  g_pub_mailbox_rr[TINY_NUM_CLASSES];
static _Atomic(uint32_t)  g_pub_mailbox_used[TINY_NUM_CLASSES];
static _Atomic(uint32_t)  g_pub_mailbox_scan[TINY_NUM_CLASSES];
static __thread uint8_t   g_tls_mailbox_registered[TINY_NUM_CLASSES];
static __thread uint8_t   g_tls_mailbox_slot[TINY_NUM_CLASSES];
static int g_mailbox_trace_en = -1;
static int g_mailbox_trace_limit = 4;
static _Atomic int g_mailbox_trace_seen[TINY_NUM_CLASSES];
// Optional: periodic slow discovery to widen 'used' even when >0 (A/B)
static int g_mailbox_slowdisc_en = -1;        // env: HAKMEM_TINY_MAILBOX_SLOWDISC (default ON)
static int g_mailbox_slowdisc_period = -1;    // env: HAKMEM_TINY_MAILBOX_SLOWDISC_PERIOD (default 256)
static __thread uint32_t  g_mailbox_fetch_tick[TINY_NUM_CLASSES];

// Thread-exit hook to release claimed slots
static pthread_once_t g_mailbox_tls_once = PTHREAD_ONCE_INIT;
static pthread_key_t  g_mailbox_tls_key;

static void mailbox_box_unregister_class(int class_idx);

static void mailbox_tls_cleanup(void* key) {
    (void)key;
    for (int i = 0; i < TINY_NUM_CLASSES; i++) {
        if (g_tls_mailbox_registered[i]) {
            mailbox_box_unregister_class(i);
        }
    }
}

static void mailbox_tls_init(void) {
    (void)pthread_key_create(&g_mailbox_tls_key, mailbox_tls_cleanup);
}

// Counters (extern from main module)
extern unsigned long long g_pub_mail_hits[];
extern unsigned long long g_rf_hit_mail[];
extern unsigned long long g_mailbox_register_calls[];
extern unsigned long long g_mailbox_slow_discoveries[];

void mailbox_box_register(int class_idx) {
    if (g_tls_mailbox_registered[class_idx]) return;
    g_mailbox_register_calls[class_idx]++;
    // One-shot visibility trace (env: HAKMEM_TINY_RF_TRACE)
    static int trace_en = -1;
    if (__builtin_expect(trace_en == -1, 0)) {
        const char* e = getenv("HAKMEM_TINY_RF_TRACE");
        trace_en = (e && atoi(e) != 0) ? 1 : 0;
    }
    pthread_once(&g_mailbox_tls_once, mailbox_tls_init);
    pthread_setspecific(g_mailbox_tls_key, (void*)1);

    uint32_t chosen = MAILBOX_SHARDS;
    for (int attempt = 0; attempt < MAILBOX_SHARDS; attempt++) {
        uint32_t idx = atomic_fetch_add_explicit(&g_pub_mailbox_rr[class_idx], 1u, memory_order_relaxed);
        idx &= (MAILBOX_SHARDS - 1u);
        uint32_t expected_claim = 0;
        if (atomic_compare_exchange_weak_explicit(&g_pub_mailbox_claimed[class_idx][idx],
                                                  &expected_claim, 1u,
                                                  memory_order_release, memory_order_relaxed)) {
            chosen = idx;
            break;
        }
    }
    if (chosen == MAILBOX_SHARDS) {
        atomic_store_explicit(&g_pub_mailbox_claimed[class_idx][0], 1u, memory_order_release);
        chosen = 0;
    }
    g_tls_mailbox_slot[class_idx] = (uint8_t)chosen;
    g_tls_mailbox_registered[class_idx] = 1;
    atomic_store_explicit(&g_pub_mailbox_entries[class_idx][chosen], (uintptr_t)0, memory_order_release);
    // Monotonic raise of used to cover chosen index
    uint32_t target = chosen + 1u;
    while (1) {
        uint32_t used = atomic_load_explicit(&g_pub_mailbox_used[class_idx], memory_order_acquire);
        if (used >= target) break;
        if (atomic_compare_exchange_weak_explicit(&g_pub_mailbox_used[class_idx], &used, target,
                                                  memory_order_acq_rel, memory_order_relaxed)) {
            break;
        }
    }
    if (trace_en) {
        static _Atomic int printed[8];
        int expected = 0;
        if (atomic_compare_exchange_strong(&printed[class_idx], &expected, 1)) {
            fprintf(stderr, "[MBTRACE] register class=%d slot=%u used=%u\n", class_idx, (unsigned)chosen, (unsigned)atomic_load_explicit(&g_pub_mailbox_used[class_idx], memory_order_relaxed));
        }
    }
}

static void mailbox_box_unregister_class(int class_idx) {
    if (!g_tls_mailbox_registered[class_idx]) return;
    uint32_t slot = g_tls_mailbox_slot[class_idx];
    atomic_store_explicit(&g_pub_mailbox_claimed[class_idx][slot], 0u, memory_order_release);
    g_tls_mailbox_registered[class_idx] = 0;
}

void mailbox_box_publish(int class_idx, SuperSlab* ss, int slab_idx) {
    mailbox_box_register(class_idx);
    // Encode entry locally (align >=1MB, lower 6 bits carry slab_idx)
    uintptr_t ent = ((uintptr_t)ss) | ((uintptr_t)slab_idx & 0x3Fu);
    uint32_t slot = g_tls_mailbox_slot[class_idx];
    tiny_debug_ring_record(TINY_RING_EVENT_MAILBOX_PUBLISH,
                           (uint16_t)class_idx,
                           ss,
                           ((uintptr_t)slot << 32) | (uintptr_t)slab_idx);
    atomic_store_explicit(&g_pub_mailbox_entries[class_idx][slot], ent, memory_order_release);
    g_pub_mail_hits[class_idx]++;
}

uintptr_t mailbox_box_peek_one(int class_idx) {
    // Optional slow-discovery (triage only) to expand used when >0
    int slow_en, period;
    if (__builtin_expect(g_mailbox_slowdisc_en == -1, 0)) {
        const char* e = getenv("HAKMEM_TINY_MAILBOX_SLOWDISC");
        g_mailbox_slowdisc_en = (!e || atoi(e) != 0) ? 1 : 0;  // default ON
    }
    slow_en = g_mailbox_slowdisc_en;
    if (slow_en) {
        uint32_t tick = ++g_mailbox_fetch_tick[class_idx];
        if (__builtin_expect(g_mailbox_slowdisc_period == -1, 0)) {
            const char* p = getenv("HAKMEM_TINY_MAILBOX_SLOWDISC_PERIOD");
            g_mailbox_slowdisc_period = p ? atoi(p) : 256;
        }
        period = g_mailbox_slowdisc_period;
        if ((tick % (uint32_t)period) == 0u) {
            // Widen used by one slot (best-effort)
            uint32_t used = atomic_load_explicit(&g_pub_mailbox_used[class_idx], memory_order_acquire);
            if (used < MAILBOX_SHARDS) {
                atomic_compare_exchange_weak_explicit(&g_pub_mailbox_used[class_idx], &used, used + 1u,
                                                      memory_order_acq_rel, memory_order_relaxed);
                g_mailbox_slow_discoveries[class_idx]++;
            }
        }
    }

    // Non-destructive peek of first non-zero entry
    uint32_t used = atomic_load_explicit(&g_pub_mailbox_used[class_idx], memory_order_acquire);
    for (uint32_t i = 0; i < used; i++) {
        uintptr_t ent = atomic_load_explicit(&g_pub_mailbox_entries[class_idx][i], memory_order_acquire);
        if (ent) return ent;
    }
    return (uintptr_t)0;
}

uintptr_t mailbox_box_fetch(int class_idx) {
    if (__builtin_expect(g_mailbox_trace_en == -1, 0)) {
        const char* e = getenv("HAKMEM_TINY_MAILBOX_TRACE");
        g_mailbox_trace_en = (e && atoi(e) != 0) ? 1 : 0;
        const char* l = getenv("HAKMEM_TINY_MAILBOX_TRACE_LIMIT");
        int v = l ? atoi(l) : 0;
        if (v > 0) g_mailbox_trace_limit = v;
    }

    uint32_t used = atomic_load_explicit(&g_pub_mailbox_used[class_idx], memory_order_acquire);
    // Optional slow discovery
    if (__builtin_expect(g_mailbox_slowdisc_en == -1, 0)) {
        const char* e = getenv("HAKMEM_TINY_MAILBOX_SLOWDISC");
        g_mailbox_slowdisc_en = (e ? ((atoi(e) != 0) ? 1 : 0) : 1);
    }
    if (__builtin_expect(g_mailbox_slowdisc_period == -1, 0)) {
        const char* p = getenv("HAKMEM_TINY_MAILBOX_SLOWDISC_PERIOD");
        int v = p ? atoi(p) : 256; g_mailbox_slowdisc_period = v;
    }
    if (g_mailbox_slowdisc_en && used < MAILBOX_SHARDS) {
        uint32_t t = ++g_mailbox_fetch_tick[class_idx];
        int period = g_mailbox_slowdisc_period;
        if ((t % (uint32_t)period) == 0u) {
            uint32_t old = used;
            if (atomic_compare_exchange_weak_explicit(&g_pub_mailbox_used[class_idx], &used, used + 1u,
                                                      memory_order_acq_rel, memory_order_relaxed)) {
                (void)old;
                g_mailbox_slow_discoveries[class_idx]++;
                used = used + 1u;
            } else {
                used = atomic_load_explicit(&g_pub_mailbox_used[class_idx], memory_order_acquire);
            }
        }
    }

    // Destructive fetch of first available entry (0..used-1)
    for (uint32_t i = 0; i < used; i++) {
        uintptr_t ent = atomic_exchange_explicit(&g_pub_mailbox_entries[class_idx][i], (uintptr_t)0,
                                                 memory_order_acq_rel);
        if (ent) {
            g_rf_hit_mail[class_idx]++;
            tiny_debug_ring_record(TINY_RING_EVENT_MAILBOX_FETCH, (uint16_t)class_idx, (void*)ent, (uintptr_t)i);
            return ent;
        }
    }
    tiny_debug_ring_record(TINY_RING_EVENT_MAILBOX_FETCH_NULL, (uint16_t)class_idx, 0, 0);
    return (uintptr_t)0;
}