flutter-concurrency
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.
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SKILL.md
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.
awaitthe result on the Main Isolate.
Workflow: Long-Lived Worker Isolate
- 1. Create a
ReceivePorton the Main Isolate. - 2. Spawn worker with
Isolate.spawn(entryPoint, mainPort.sendPort). - 3. In worker, create its own
ReceivePortand send itsSendPortback. - 4. Store worker's
SendPortfor bidirectional communication. - 5. Close ports and kill isolate on dispose.
See examples 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:
FutureBuilderre-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 testpasses.
References
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
Files
3- SKILL.md
b4add4aaf02.7 KB - evals/evals.json
0ea8ae49d92.7 KB - references/isolate-examples.md
0987c356832.6 KB
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