Crate hotpath_drain 

Lock-free event transport between instrumented threads and background workers.

Each producing thread owns a chunked SPSC queue: it appends events into fixed-size chunks with plain stores and publishes them with a single Release store of the chunk’s len - no mutex, no RMW atomic on the hot path. Chunks form a linked list, so the queue is unbounded.

A single consumer per registry (the subsystem’s background worker) sweeps all registered queues periodically: it Acquire-loads each chunk’s len, reads the published prefix, and frees fully consumed chunks. Producer and consumer touch disjoint slot ranges by construction, so a queue is safe to drain at any moment - including queues of threads parked at shutdown, which is what guarantees a complete final report.

Safety invariants:

• Only the owning thread writes slots and the len/next of its tail chunk.
• The consumer only reads slots below the published len and only frees a chunk after fully consuming it and observing its next pointer.
• Single consumer per registry, enforced by the registry’s internal mutex (locked only at thread registration and during sweeps - never on the event hot path).

Structs

EventProducer

The owning thread’s write handle, stored in a thread_local.

EventQueue

One thread’s event queue: a linked list of chunks. The owning thread appends via its EventProducer; the registry’s consumer drains.

EventQueueRegistry

All live per-thread queues for one event type, plus the gate that tells producers whether a worker is consuming.

Constants

CHUNK_SIZE