flutter-handling-concurrency

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.

Decision Matrix: Async vs. Isolates

Apply the following conditional logic to determine the correct concurrency approach:

• If the task is I/O bound (e.g., HTTP request, database read) -> Use async/await on the Main Isolate.
• If the task is CPU-bound but executes quickly (< 16ms) -> Use async/await on the Main Isolate.
• If the task is CPU-bound, takes significant time, and runs once (e.g., parsing a massive JSON payload) -> Use Isolate.run().
• If the task requires continuous or repeated background processing with multiple messages passed over time -> Use Isolate.spawn() with ReceivePort and SendPort.