hakmem/core/hakmem_shared_pool.c

#include "hakmem_shared_pool.h"
#include "hakmem_tiny_superslab.h"
#include "hakmem_tiny_superslab_constants.h"

#include <stdlib.h>
#include <string.h>

// Phase 12-2: SharedSuperSlabPool skeleton implementation
// Goal:
//   - Centralize SuperSlab allocation/registration
//   - Provide acquire_slab/release_slab APIs for later refill/free integration
//   - Keep logic simple & conservative; correctness and observability first.
//
// Notes:
//   - Concurrency: protected by g_shared_pool.alloc_lock for now.
//   - class_hints is best-effort: read lock-free, written under lock.
//   - LRU hooks left as no-op placeholders.

SharedSuperSlabPool g_shared_pool = {
    .slabs        = NULL,
    .capacity     = 0,
    .total_count  = 0,
    .active_count = 0,
    .alloc_lock   = PTHREAD_MUTEX_INITIALIZER,
    .class_hints  = { NULL },
    .lru_head     = NULL,
    .lru_tail     = NULL,
    .lru_count    = 0
};

static void
shared_pool_ensure_capacity_unlocked(uint32_t min_capacity)
{
    if (g_shared_pool.capacity >= min_capacity) {
        return;
    }

    uint32_t new_cap = g_shared_pool.capacity ? g_shared_pool.capacity : 16;
    while (new_cap < min_capacity) {
        new_cap *= 2;
    }

    SuperSlab** new_slabs = (SuperSlab**)realloc(g_shared_pool.slabs,
                                                 new_cap * sizeof(SuperSlab*));
    if (!new_slabs) {
        // Allocation failure: keep old state; caller must handle NULL later.
        return;
    }

    // Zero new entries to keep scanning logic simple.
    memset(new_slabs + g_shared_pool.capacity, 0,
           (new_cap - g_shared_pool.capacity) * sizeof(SuperSlab*));

    g_shared_pool.slabs    = new_slabs;
    g_shared_pool.capacity = new_cap;
}

void
shared_pool_init(void)
{
    // Idempotent init; safe to call from multiple early paths.
    // pthread_mutex_t with static initializer is already valid.
    pthread_mutex_lock(&g_shared_pool.alloc_lock);
    if (g_shared_pool.capacity == 0 && g_shared_pool.slabs == NULL) {
        shared_pool_ensure_capacity_unlocked(16);
    }
    pthread_mutex_unlock(&g_shared_pool.alloc_lock);
}

/*
 * Internal: allocate and register a new SuperSlab for the shared pool.
 *
 * Phase 12 NOTE:
 *  - We MUST use the real superslab_allocate() path so that:
 *      - backing memory is a full SuperSlab region (1–2MB),
 *      - header/layout are initialized correctly,
 *      - registry integration stays consistent.
 *  - shared_pool is responsible only for:
 *      - tracking pointers,
 *      - marking per-slab class_idx as UNASSIGNED initially.
 *    It does NOT bypass registry/LRU.
 *
 * Caller must hold alloc_lock.
 */
static SuperSlab*
shared_pool_allocate_superslab_unlocked(void)
{
    // Use size_class 0 as a neutral hint; Phase 12 per-slab class_idx is authoritative.
    extern SuperSlab* superslab_allocate(uint8_t size_class);
    SuperSlab* ss = superslab_allocate(0);
    if (!ss) {
        return NULL;
    }

    // superslab_allocate() already:
    //  - zeroes slab metadata / remote queues,
    //  - sets magic/lg_size/etc,
    //  - registers in global registry.
    // For shared-pool semantics we normalize all slab class_idx to UNASSIGNED.
    int max_slabs = ss_slabs_capacity(ss);
    for (int i = 0; i < max_slabs; i++) {
        ss->slabs[i].class_idx = 255; // UNASSIGNED
    }

    if (g_shared_pool.total_count >= g_shared_pool.capacity) {
        shared_pool_ensure_capacity_unlocked(g_shared_pool.total_count + 1);
        if (g_shared_pool.total_count >= g_shared_pool.capacity) {
            // Pool table expansion failed; leave ss alive (registry-owned),
            // but do not treat it as part of shared_pool.
            return NULL;
        }
    }

    g_shared_pool.slabs[g_shared_pool.total_count] = ss;
    g_shared_pool.total_count++;
    // Not counted as active until at least one slab is assigned.
    return ss;
}

SuperSlab*
shared_pool_acquire_superslab(void)
{
    // Phase 12 debug safety:
    //   If shared backend is disabled at Box API level, this function SHOULD NOT be called.
    //   But since bench currently SEGVs here even with legacy forced, treat this as a hard guard:
    //   we early-return error instead of touching potentially-bad state.
    //
    //   This isolates shared_pool from the current crash so we can validate legacy path first.
    // FIXED: Remove the return -1; that was preventing operation

    shared_pool_init();

    pthread_mutex_lock(&g_shared_pool.alloc_lock);

    // For now, always allocate a fresh SuperSlab and register it.
    // More advanced reuse/GC comes later.
    SuperSlab* ss = shared_pool_allocate_superslab_unlocked();

    pthread_mutex_unlock(&g_shared_pool.alloc_lock);
    return ss;
}

int
shared_pool_acquire_slab(int class_idx, SuperSlab** ss_out, int* slab_idx_out)
{
    // Phase 12: real shared backend is enabled; this function must be correct & safe.
    // Invariants (callers rely on):
    //  - On success, *ss_out != NULL, 0 <= *slab_idx_out < SLABS_PER_SUPERSLAB_MAX.
    //  - The chosen slab has meta->class_idx == class_idx and capacity > 0.
    if (!ss_out || !slab_idx_out) {
        return -1;
    }
    if (class_idx < 0 || class_idx >= TINY_NUM_CLASSES_SS) {
        return -1;
    }

    shared_pool_init();

    // Fast-path hint: read without lock (best-effort).
    SuperSlab* hint = g_shared_pool.class_hints[class_idx];
    if (hint) {
        // Scan for a free, unassigned slab in this SuperSlab.
        uint32_t bitmap = hint->slab_bitmap;
        for (int i = 0; i < SLABS_PER_SUPERSLAB_MAX; i++) {
            uint32_t bit = (1u << i);
            if ((bitmap & bit) == 0 && hint->slabs[i].class_idx == 255) {
                // Tentative claim: upgrade under lock to avoid races.
                pthread_mutex_lock(&g_shared_pool.alloc_lock);
                // Re-check under lock.
                bitmap = hint->slab_bitmap;
                if ((bitmap & bit) == 0 && hint->slabs[i].class_idx == 255) {
                    hint->slab_bitmap |= bit;
                    hint->slabs[i].class_idx = (uint8_t)class_idx;
                    hint->active_slabs++;
                    if (hint->active_slabs == 1) {
                        g_shared_pool.active_count++;
                    }
                    *ss_out       = hint;
                    *slab_idx_out = i;
                    pthread_mutex_unlock(&g_shared_pool.alloc_lock);
                    return 0;
                }
                pthread_mutex_unlock(&g_shared_pool.alloc_lock);
                break; // fall through to slow path
            }
        }
    }

    // Slow path: lock and scan all registered SuperSlabs.
    pthread_mutex_lock(&g_shared_pool.alloc_lock);

    for (uint32_t idx = 0; idx < g_shared_pool.total_count; idx++) {
        SuperSlab* ss = g_shared_pool.slabs[idx];
        if (!ss) {
            continue;
        }
        uint32_t bitmap = ss->slab_bitmap;
        for (int i = 0; i < SLABS_PER_SUPERSLAB_MAX; i++) {
            uint32_t bit = (1u << i);
            if ((bitmap & bit) == 0 && ss->slabs[i].class_idx == 255) {
                // Assign this slab to class_idx.
                ss->slab_bitmap |= bit;
                ss->slabs[i].class_idx = (uint8_t)class_idx;
                ss->active_slabs++;
                if (ss->active_slabs == 1) {
                    g_shared_pool.active_count++;
                }
                // Update hint.
                g_shared_pool.class_hints[class_idx] = ss;
                *ss_out       = ss;
                *slab_idx_out = i;
                pthread_mutex_unlock(&g_shared_pool.alloc_lock);
                return 0;
            }
        }
    }

    // No existing space: allocate a new SuperSlab and take its first slab.
    SuperSlab* ss = shared_pool_allocate_superslab_unlocked();
    if (!ss) {
        pthread_mutex_unlock(&g_shared_pool.alloc_lock);
        return -1;
    }

    int slab_idx = 0;
    ss->slab_bitmap       |= (1u << slab_idx);
    ss->slabs[slab_idx].class_idx = (uint8_t)class_idx;
    ss->active_slabs      = 1;
    g_shared_pool.active_count++;

    g_shared_pool.class_hints[class_idx] = ss;

    *ss_out       = ss;
    *slab_idx_out = slab_idx;

    pthread_mutex_unlock(&g_shared_pool.alloc_lock);
    return 0;
}

void
shared_pool_release_slab(SuperSlab* ss, int slab_idx)
{
    if (!ss) {
        return;
    }
    if (slab_idx < 0 || slab_idx >= SLABS_PER_SUPERSLAB_MAX) {
        return;
    }

    pthread_mutex_lock(&g_shared_pool.alloc_lock);

    TinySlabMeta* meta = &ss->slabs[slab_idx];
    if (meta->used != 0) {
        // Not actually empty; nothing to do.
        pthread_mutex_unlock(&g_shared_pool.alloc_lock);
        return;
    }

    uint32_t bit = (1u << slab_idx);
    if (ss->slab_bitmap & bit) {
        ss->slab_bitmap &= ~bit;
        uint8_t old_class = meta->class_idx;
        meta->class_idx = 255; // UNASSIGNED

        if (ss->active_slabs > 0) {
            ss->active_slabs--;
            if (ss->active_slabs == 0 && g_shared_pool.active_count > 0) {
                g_shared_pool.active_count--;
            }
        }

        // Invalidate class hint if it pointed here and this superslab has no free slab
        // for that class anymore; for now we do a simple best-effort clear.
        if (old_class < TINY_NUM_CLASSES_SS &&
            g_shared_pool.class_hints[old_class] == ss) {
            // We could rescan ss for another matching slab; to keep it cheap, just clear.
            g_shared_pool.class_hints[old_class] = NULL;
        }
    }

    // TODO Phase 12-4+: if ss->active_slabs == 0, consider GC / unmap.

    pthread_mutex_unlock(&g_shared_pool.alloc_lock);
}