Struct KhpdHeader 

#[repr(C, align(64))]
pub struct KhpdHeader {
    pub magic: u64,
    pub capacity: u64,
    pub owner_pid: AtomicU64,
    pub epoch: AtomicU64,
    pub _pad_meta: [u8; 24],
    pub tail: AtomicI64,
    pub _pad_tail: [u8; 56],
    pub head: AtomicI64,
    pub _pad_head: [u8; 56],
}

File header. Cache-line aligned. head and tail each get their own cache line to prevent producer and consumer counters from invalidating each other.

Fields

magic: u64

Magic constant.

capacity: u64

Number of publication lines; always a power of two.

owner_pid: AtomicU64

Pid of the owner process; informational. Cleared on close_owner().

epoch: AtomicU64

Epoch counter advanced on owner shutdown.

_pad_meta: [u8; 24]

Padding to push tail to its own cache line.

tail: AtomicI64

Producer counter. Owner fetch_add(1) per published line.

_pad_tail: [u8; 56]

Padding to push head to its own line.

head: AtomicI64

Consumer counter. Thieves CAS this to claim a line.

_pad_head: [u8; 56]

Padding to round the header to two whole cache lines after head.