Module broadcast 

Broadcast Channel for multi-consumer streaming.

BroadcastChannel<T> implements a shared ring buffer with per-subscriber cursors for single-producer, multiple-consumer (SPMC) broadcast. Designed for Ring 0 hot path: zero allocations after construction, lock-free reads and writes.

Design

• Pre-allocated ring buffer with power-of-2 capacity and bitmask indexing
• Lock-free hot path: broadcast(), read(), slowest_cursor() use only atomics
• Fixed-size cursor array with O(1) direct indexing by subscriber ID
• Cache-padded cursor slots (64-byte aligned) to prevent false sharing
• Single producer via broadcast()
• Dynamic subscribers via subscribe() and unsubscribe()
• Configurable slow subscriber policies: Block, DropSlow, SkipForSlow
• Per-subscriber lag tracking for backpressure monitoring

Key Principle

Broadcast is derived from query plan analysis, not user configuration. The planner determines when multiple MVs read from the same source and auto-upgrades to broadcast mode.

Safety

The single-writer invariant is upheld by the DAG executor, which ensures exactly one thread calls broadcast() on any given channel. Multiple threads may call read() with distinct subscriber IDs.

Performance Targets

Operation	Target
broadcast()	< 100ns (2 subscribers)
read()	< 50ns
subscribe()	O(1), CAS on slot (Ring 2 only)

Structs

BroadcastChannel

Broadcast channel for multi-consumer scenarios.

BroadcastConfig

Broadcast channel configuration.

BroadcastConfigBuilder

Builder for BroadcastConfig.

SubscriberInfo

Information about a subscriber.

Enums

BroadcastError

Broadcast channel errors.

SlowSubscriberPolicy

Slow subscriber handling policy.

Constants

DEFAULT_BROADCAST_CAPACITY

Default buffer capacity (power of 2).

DEFAULT_LAG_WARNING_THRESHOLD

Default lag warning threshold.

DEFAULT_MAX_SUBSCRIBERS

Default maximum subscribers.

DEFAULT_SLOW_SUBSCRIBER_TIMEOUT

Default slow subscriber timeout.