flutter-handling-concurrency

SKILL.md

Offload CPU-intensive tasks to background isolates while keeping Flutter UIs responsive.

Provides three concurrency patterns: async/await for I/O-bound work, Isolate.run() for one-off heavy computations, and Isolate.spawn() with message passing for persistent background workers

Includes a decision matrix to choose between async operations and isolates based on task type (I/O vs. CPU-bound) and execution frequency

Covers three complete workflows with step-by-step task checklists: standard async UI with FutureBuilder, short-lived isolate offloading, and long-lived bidirectional worker communication

Provides three runnable code examples demonstrating FutureBuilder patterns, JSON decoding in isolates, and ReceivePort/SendPort message passing architecture

Managing Dart Concurrency and Isolates

Contents

Core Concepts

Decision Matrix: Async vs. Isolates

Workflows

Implementing Standard Asynchronous UI

Offloading Short-Lived Heavy Computation

Establishing Long-Lived Worker Isolates

Examples

Core Concepts

Dart utilizes a single-threaded execution model driven by an Event Loop (comparable to the iOS main loop). By default, all Flutter application code runs on the Main Isolate.

Asynchronous Operations (async/await): Use for non-blocking I/O tasks (network requests, file access). The Event Loop continues processing other events while waiting for the Future to complete.

Isolates: Dart's implementation of lightweight threads. Isolates possess their own isolated memory and do not share state. They communicate exclusively via message passing.

Main Isolate: The default thread where UI rendering and event handling occur. Blocking this isolate causes UI freezing (jank).

Worker Isolate: A spawned isolate used to offload CPU-bound tasks (e.g., decoding large JSON blobs) to prevent Main Isolate blockage.