---
name: flutter-concurrency
description: Execute long-running tasks in background isolates to keep the UI responsive. Use when performing heavy computations, parsing large datasets, or choosing between async/await and isolates.
metadata:
  triggers:
    files:
    - '**/*isolate*.dart'
    - '**/*worker*.dart'
    keywords:
    - Isolate
    - compute
    - Isolate.run
    - Isolate.spawn
    - ReceivePort
    - SendPort
    - background
---
# Dart Concurrency and Isolates

## **Priority: P1 (HIGH)**

## Core Concepts

Dart uses a single-threaded event loop. All Flutter code runs on the Main Isolate by default. Blocking it causes jank.

- **async/await**: For non-blocking I/O (network, file). The event loop continues while waiting.
- **Isolates**: Dart's lightweight threads with isolated memory. Communicate via message passing only.

## Decision Matrix

| Condition | Approach |
|-----------|----------|
| I/O bound (HTTP, database) | `async`/`await` on Main Isolate |
| CPU-bound, < 16ms | `async`/`await` on Main Isolate |
| CPU-bound, one-off heavy task | `Isolate.run()` |
| Continuous background processing | `Isolate.spawn()` with ports |

## Workflow: Offloading Heavy Computation

- [ ] 1. Identify the CPU-bound operation blocking the UI.
- [ ] 2. Extract computation into a standalone top-level or static function.
- [ ] 3. Ensure the function accepts exactly one argument (Isolate constraint).
- [ ] 4. Call `Isolate.run(() => myFunction(data))`.
- [ ] 5. `await` the result on the Main Isolate.

## Workflow: Long-Lived Worker Isolate

- [ ] 1. Create a `ReceivePort` on the Main Isolate.
- [ ] 2. Spawn worker with `Isolate.spawn(entryPoint, mainPort.sendPort)`.
- [ ] 3. In worker, create its own `ReceivePort` and send its `SendPort` back.
- [ ] 4. Store worker's `SendPort` for bidirectional communication.
- [ ] 5. Close ports and kill isolate on dispose.

See [examples](references/isolate-examples.md) for complete code.

## Anti-Patterns

- **No JSON parsing on Main Isolate**: Large JSON decoding (>1MB) blocks frames. Use `Isolate.run`.
- **No shared mutable state**: Isolates cannot share memory. Pass data via messages.
- **No FutureBuilder in build without caching**: `FutureBuilder` re-fires on every rebuild if the future is created inline.

## Verification

- [ ] No frame drops during heavy computation (check with DevTools).
- [ ] Worker isolates are disposed when no longer needed.
- [ ] `flutter test` passes.

## References

- [Isolate Examples](references/isolate-examples.md)

## Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:
- Dart Concurrency and Isolates


---
Source attribution: HoangNguyen0403
Original project: https://github.com/HoangNguyen0403/agent-skills-standard
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 Gabriel Moreira

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: HoangNguyen0403
Original project: https://github.com/HoangNguyen0403/agent-skills-standard
Attribution basis: Upstream repository explicitly recorded in package mirror path

Fields of work: Development & Engineering
Roles: Frontend Developer, Mobile Developer
Specialties: Backend, Mobile
Tools: Dart
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: b4add4aaf0b8d24a7d05f9f2c39ba82eaaa6af393ed79de2add1a9484d91c5e1