Struct SegmentHeader 

pub struct SegmentHeader {

    pub magic: [u8; 8],
    pub version: u32,
    pub header_size: u32,
    pub total_size: u64,
    pub max_payload_size: u32,
    pub inline_threshold: u32,
    pub max_guests: u32,
    pub bipbuf_capacity: u32,
    pub peer_table_offset: u64,
    pub var_pool_offset: u64,
    pub heartbeat_interval: u64,
    pub host_goodbye: AtomicU32,
    pub num_var_slot_classes: u32,
    pub current_size: AtomicU64,
    /* private fields */
}

The segment header lives at offset 0 of every roam SHM segment.

All fields are set by the host at creation time and treated as read-only by guests after attach — except host_goodbye and current_size, which the host may update at runtime.

r[impl shm.segment] r[impl shm.segment.header] r[impl shm.segment.config]

Fields

magic: [u8; 8]

“ROAMHUB\x07” — identifies a v7 roam SHM segment.

version: u32

Segment format version (currently 7).

header_size: u32

Always 128 — allows future extension without breaking older readers.

total_size: u64

Total size of the segment in bytes (set at creation).

max_payload_size: u32

Maximum payload size in bytes.

inline_threshold: u32

Inline threshold: payloads ≤ this go inline; larger ones use a slot ref. 0 means use the default (256 bytes).

max_guests: u32

Maximum number of guests (≤ 255).

bipbuf_capacity: u32

BipBuffer data region size per direction, in bytes.

peer_table_offset: u64

Byte offset of the peer table from the start of the segment.

var_pool_offset: u64

Byte offset of the shared VarSlotPool from the start of the segment.

heartbeat_interval: u64

Heartbeat interval in nanoseconds; 0 = heartbeats disabled.

host_goodbye: AtomicU32

Set to non-zero by the host during orderly shutdown.

num_var_slot_classes: u32

Number of var-slot size classes described at var_pool_offset.

current_size: AtomicU64

Current segment size in bytes. May grow if extents are appended.

Implementations

impl SegmentHeader

pub unsafe fn init(&mut self, init: SegmentHeaderInit)

Write initial values into a zeroed header.

Safety

self must point into exclusively-owned, zeroed memory.

pub fn validate(&self) -> Result<(), &'static str>

Validate that the header looks like a v7 roam segment.

Returns Err with a description if validation fails.

r[impl shm.segment.magic.v7]

pub fn effective_inline_threshold(&self) -> u32

Read the effective inline threshold (substituting the default if 0).

pub fn current_size(&self) -> u64

Read the current segment size.

pub fn host_goodbye(&self) -> bool

Check whether the host has raised the goodbye flag.