Isolate.spawn

Learn new isolates with Isolate.spawn.

Isolate.spawn signature

Isolate.spawn schedules a new isolate and returns Future<void>. The future completes when the isolate has been started — it does not wait for the work to finish.

The first parameter is the entryPoint of type void Function(List<String>). The second is a List<String> message list; typically the first element is a SendPort.

Example: await Isolate.spawn(worker, ['data']);. With await you wait for the isolate to be started; without it the main isolate continues immediately.

Passing data with spawn

The list passed as the second argument to spawn is copied into the isolate. Each element must be serializable (primitive, SendPort, List, Map).

A common pattern is to make the first element a SendPort: Isolate.spawn(worker, [port.sendPort, 'gorev-1']). The isolate then sends its result back through this port.

Note: closure variables cannot be passed. entryPoint can only read the parameter list.

Exercise Get a single result with Isolate.run

Make main async. Add var result = await Isolate.run(() => 6 * 7); and print it with print(result);.

Show example solution

import 'dart:isolate';

void main() async {
  var result = await Isolate.run(() => 6 * 7);
  print(result);
}

Test yourself

spawn return type

Future<____> IsolateSpawnFunction() => Isolate.spawn(entry, args);

Show answer

Future<void> IsolateSpawnFunction() => Isolate.spawn(entry, args);

What is the return type of Isolate.spawn?
- void
- Future<void>
- Stream<void>
- Isolate
Show answer

Future<void> — spawn returns Future<void> — it completes when the isolate has started.
Match the spawn parts

Future<void>

spawn return type
entryPoint

Function to run
List<String>

Message list
SendPort

Reply channel

Next lesson: SendPort

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies