#IndexBus Overview

IndexBus is the bounded shared-memory transport substrate at the base of the ByteOr stack. It provides deterministic lane semantics, zero-copy IPC, and bounded-memory data flow between cooperating processes.

#What IndexBus Does

IndexBus solves the IPC problem for real-time systems: move data between processes on the same host with deterministic behavior, bounded memory, and no serialization overhead.

• Shared-memory regions with repr(C) layouts for cross-language interoperability
• Deterministic lane semantics — well-defined capacity, backpressure, and ordering guarantees
• Router and merge infrastructure — fanout and fan-in with bounded memory
• Zero-copy — no serialization, no allocation in the hot path

IndexBus is open source (Apache-2.0 / MIT) and can be used independently of ByteOr.

#Lane Kinds

IndexBus defines four lane kinds, each with specific semantics:

#Backpressure

When a lane is full, behavior depends on the on_full policy:

• Block — the producer waits until space is available
• Drop — the oldest entry is overwritten

#Start With These References

#Architecture

┌──────────┐    ┌───────────────┐    ┌──────────┐
│ Producer  │───▶│  SHM Region   │───▶│ Consumer │
│ Process   │    │  (lanes +     │    │ Process  │
│           │    │   headers)    │    │          │
└──────────┘    └───────────────┘    └──────────┘

Processes communicate through shared-memory regions. Each region contains lanes with headers that track read and write positions. The repr(C) layout ensures any language with C FFI can participate.

#Router and Merge Infrastructure

For complex topologies, IndexBus provides:

• Routers — distribute messages from one producer to multiple lanes based on routing policy
• Merges — combine messages from multiple lanes into a single output lane

Both operate with bounded memory and deterministic ordering guarantees.

#v1 Semantics

The v1 semantics define the normative behavior for lane operations:

• Initialization — region and lane setup, header validation
• Write — bounded write with on_full policy enforcement
• Read — position-tracked reads with ordering guarantees
• Capacity — fixed at creation time, enforced throughout lifetime
• Ordering — guaranteed within a lane, defined by lane kind across lanes

#Production Requirements

IndexBus production deployments require:

• SHM files on tmpfs or hugetlbfs mounts
• No stale SHM files from previous runs
• Correct file permissions (cooperating-process trust model)
• Adequate memory for all lane capacities
• Router and merge infrastructure sized for the topology

#Performance

IndexBus is designed for high-throughput, low-latency IPC:

• No system calls in the hot path
• No serialization or allocation
• Cache-line-aware layout for producer/consumer pairs
• Spin-wait or backoff wait strategies configurable per deployment

See Performance Tuning for operational guidance.

#Deeper Technical Sources

• Rustdoc entry points