Module barrier 

Checkpoint barrier types and cross-thread injection. Checkpoint barrier protocol for distributed snapshots.

This module implements the Chandy-Lamport style barrier protocol for consistent distributed checkpoints. Barriers flow through the dataflow graph alongside events, triggering state snapshots at each operator.

Protocol Overview

1. The coordinator injects a CheckpointBarrier into all sources
2. Barriers propagate through operators via StreamMessage::Barrier
3. Operators with multiple inputs align barriers before snapshotting
4. Once all sinks acknowledge, the checkpoint is complete

Fast Path

The CheckpointBarrierInjector uses a packed AtomicU64 command word for cross-thread signaling. The poll fast path (no pending barrier) is a single atomic load — typically < 10ns.

Modules

flags

Barrier flags — packed into the flags field.

Structs

BarrierPollHandle

Handle used by source operators to poll for pending barriers.

CheckpointBarrier

A checkpoint barrier that flows through the dataflow graph.

CheckpointBarrierInjector

Cross-thread barrier injector for source operators.

Enums

StreamMessage

A message that flows through streaming channels.