# Blocking call on a critical executor

Rule ID: concurrency.main-actor-blocking@1.0.0. Availability below refers to source-scan at product 524fa07e.

## V-EXEC-09 — Blocking call on a critical executor

Blocking call on a critical executor. It examines isolation, executor, scheduler, and execution-domain relationships.

### Availability

Not available in source-scan. There is no source-scan flag to activate this condition.

A separate [experimental source preview](https://docs.swift-analyzer.com/guides/experimental/) recognizes a limited local pattern for this condition:

```text
"$ANALYZER" experimental-scan <path> --rule execution.blocking-in-concurrency-context --format json
```

Use the terminal from [Installation](https://docs.swift-analyzer.com/get-started/installation/), with ANALYZER set, and replace `<path>` with a Swift file or directory. This preview is not compiler-backed source-scan coverage.

### Example and action

Illustrative pattern only. This is not a complete runnable package or a reproduced source-scan result. Helper APIs and omitted context must be supplied by the application.

```swift
@MainActor func refresh() {
    Thread.sleep(forTimeInterval: 2)
}
```

Make the required context explicit at the boundary. Review ordering, lifetime and transferred values before adding a task or changing isolation.

```swift
@MainActor func refresh() async throws {
    try await Task.sleep(for: .seconds(2))
}
```

### Intended analysis

Intended reasoning: Compare the required execution or isolation context with recognized context transitions and use sites. Actor context, task context and physical thread identity are different facts; suspension alone does not prove a thread hop. Required evidence: isolation, executor, scheduler, and path facts

### Assumptions and unknown

The relevant facts must be admitted for the selected immutable build world. Unknown aliases, external effects, unsupported source forms or incomplete consumers can prevent a conclusion. Availability in this workflow is stated above; the illustration does not expand that availability.

### Evidence and interpretation

The target catalog describes the intended condition. It is not evidence of an active source-scan diagnostic.

Historical evidence at 4558458d: recovery-required (historical qualification is incomplete and needs further evidence). That evidence has not been requalified for this product revision.

[How we validate checks](https://docs.swift-analyzer.com/concepts/validation/) explains the evidence boundary. [Foundations](https://docs.swift-analyzer.com/concepts/foundations/) separates method assumptions from implementation claims.


---

Language: en
Canonical: https://docs.swift-analyzer.com/catalog/concurrency.main-actor-blocking/
Product revision: 524fa07e0ae4153c84ac12ae9eb6559df89ec2be
Catalog revision: 4558458d
Documentation digest: 1f17ba58ab08627e0de898f1442067b09e960b48cd5605d6529e9275f8930d68
Channel: pre-prod; maturity: experimental; access: owner-provided checkout.