# Read-Time Join

> A mechanism that lets a caller whose question a live declared scope already covers read that run's published result and its standing, writing nothing, so it cannot deadlock, be orphaned or need cleanup.

Record: `architecture:read-time-join`
Kind: mechanism
Layer: [Execution Core](https://banes-lab.com/records/layer/execution-core.md)
Severity: recommended
Scope: run, invocation
Canonical: https://banes-lab.com/ontology#architecture-read-time-join

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Write Scope and Read Population](https://banes-lab.com/records/architecture/write-scope-and-read-population.md) and before [One-Sided Liveness](https://banes-lab.com/records/architecture/one-sided-liveness.md).

## Repair

- Refactored by: Test Coverage First, Join by Reading the Published Result
- Detected by: two runs over one covered question, or a caller waiting on another run's handle
- Violated by: attaching a second caller to a running process, or starting a duplicate run a live scope already covers
- Measured by: duplicate runs a live scope covered
- Enforced by: coordination review

## Requires

- [Joiner](https://banes-lab.com/records/lexicon/joiner.md)
- [Read Population](https://banes-lab.com/records/lexicon/read-population.md)

## Reinforces

- [Write Scope and Read Population](https://banes-lab.com/records/architecture/write-scope-and-read-population.md)

## Enables

- [Shared Invocation](https://banes-lab.com/records/lexicon/shared-invocation.md)

## Contracts

- [Invocation Join](https://banes-lab.com/records/algorithms/invocation-join.md)

## Severity

- [recommended](https://banes-lab.com/records/vocabulary/severity-recommended.md)

## Category

- [Coordination Surfaces](https://banes-lab.com/records/architecture-category/coordination-surfaces.md)

## Linked from

- [Coordination Surfaces](https://banes-lab.com/ontology/principles/architecture-category-coordination-surfaces.md)
- [Coordination Surfaces](https://banes-lab.com/ontology/lexicon/lexicon-category-coordination-surfaces.md)
- [Coordination](https://banes-lab.com/ontology/algorithms/algorithms-domain-coordination.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)

## Evidence in the code

- [models/invocation.model.md](https://banes-lab.com/source/coordination/models/invocation.model.md.md)