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METHODS
  Allocation
        my $idx = $pool->alloc;             # block until available
        my $idx = $pool->alloc($timeout);   # with timeout (seconds)
        my $idx = $pool->alloc(0);          # non-blocking
        my $idx = $pool->try_alloc;         # non-blocking (alias)

    Returns slot index on success, "undef" on failure/timeout.

        $pool->free($idx);                  # release slot (returns true/false)

  Batch Operations
        my $slots = $pool->alloc_n($n);            # allocate N slots (blocking)
        my $slots = $pool->alloc_n($n, $timeout);  # with timeout
        my $slots = $pool->alloc_n($n, 0);         # non-blocking
        # returns arrayref of indices, or undef (all-or-nothing)

        my $freed = $pool->free_n(\@indices);      # batch free, returns count freed
        # single used-decrement + single futex wake (faster than N individual frees)

        my $slots = $pool->allocated_slots;  # arrayref of all allocated indices

  Data Access
        my $val = $pool->get($idx);         # read slot
        $pool->set($idx, $val);             # write slot

    For I64/I32 variants:

        my $ok  = $pool->cas($idx, $old, $new);     # atomic CAS, returns bool
        my $old = $pool->cmpxchg($idx, $old, $new); # atomic CAS, returns old value
        my $old = $pool->xchg($idx, $val);          # atomic exchange, returns old
        my $val = $pool->add($idx, $delta);          # atomic add, returns new value
        my $val = $pool->incr($idx);                 # atomic increment
        my $val = $pool->decr($idx);                 # atomic decrement

    For Str variant:

        my $max = $pool->max_len;           # maximum string length

  Raw Pointers
        my $ptr = $pool->ptr($idx);     # raw C pointer to slot data (UV)
        my $ptr = $pool->data_ptr;      # pointer to start of data section

    "ptr" returns the memory address of a slot's data as an unsigned
    integer. Use with FFI::Platypus, OpenGL "_c" functions, or XS code that
    needs a "void*".

    "data_ptr" returns the base of the contiguous data region. Slots are
    laid out as "data_ptr + idx * elem_size".

    Warning: The returned pointer becomes dangling if the pool object is
    destroyed. Do not use after the pool goes out of scope.

  Zero-Copy Access
        my $sv = $pool->slot_sv($idx);  # SV backed by slot memory

    Returns a read-only scalar whose PV points directly into the shared
    memory slot. Reading the scalar reads the slot with no "memcpy". Useful
    for large slots where avoiding copy matters.

    The scalar holds a reference to the pool object, keeping it alive for as
    long as the scalar (or any copy of it) is live. However, the scalar
    still reflects the current contents of the slot: if the slot is free()d
    and later re-allocated, reads will see the new data. To modify the slot,
    use set().

  Status
        my $ok  = $pool->is_allocated($idx);
        my $cap = $pool->capacity;
        my $esz = $pool->elem_size;
        my $n   = $pool->used;              # allocated count
        my $n   = $pool->available;         # free count
        my $pid = $pool->owner($idx);       # PID of allocator

  Recovery
        my $n = $pool->recover_stale;       # free slots owned by dead PIDs
        $pool->reset;                       # free all slots (exclusive access only)

  Guards
        my ($idx, $guard) = $pool->alloc_guard;           # auto-free on scope exit
        my ($idx, $guard) = $pool->alloc_guard($timeout);
        my ($idx, $guard) = $pool->try_alloc_guard;       # non-blocking

  Convenience
        my $idx = $pool->alloc_set($val);           # alloc + set
        my $idx = $pool->alloc_set($val, $timeout); # with timeout
        my $idx = $pool->try_alloc_set($val);       # non-blocking

        $pool->each_allocated(sub { my $idx = shift; ... });

  Common Methods
        my $p  = $pool->path;        # backing file (undef if anon)
        my $fd = $pool->memfd;       # memfd fd (-1 if not memfd)
        $pool->sync;                 # msync to disk
        $pool->unlink;               # remove backing file
        my $s  = $pool->stats;       # diagnostic hashref

   eventfd Integration
        my $fd = $pool->eventfd;           # create eventfd
        $pool->eventfd_set($fd);           # use existing fd
        my $fd = $pool->fileno;            # current eventfd (-1 if none)
        $pool->notify;                     # signal eventfd
        my $n  = $pool->eventfd_consume;   # drain counter

STATS
    stats() returns a hashref with diagnostic counters. All values are
    approximate under concurrency.

    "capacity" — total slot count (immutable)
    "elem_size" — bytes per slot (immutable)
    "used" — currently allocated slot count
    "available" — currently free slot count ("capacity - used")
    "waiters" — processes currently blocked on "alloc"
    "mmap_size" — total mmap region size in bytes
    "allocs" — cumulative successful allocations
    "frees" — cumulative frees (including stale recovery)
    "waits" — "alloc" calls that entered the retry loop
    "timeouts" — "alloc" calls that timed out
    "recoveries" — slots freed by "recover_stale"

SECURITY