Flutter Isolate vs Future


I might have the wrong idea of Isolate and Future. Please help me to clear it up. Here is my understanding of both subjects.

Isolate: Isolates run code in its own event loop, and each event may run smaller tasks in a nested microtask queue.

Future: A Future is used to represent a potential value, or error, that will be available at some time in the future.

My confusions are:

  1. The doc says Isolate has it own loop? I feel like having its own event queue makes more sense to me, am I wrong?

  2. Is future running asynchronously on the main Isolate? I’m assuming future task actually got placed at the end of event queue so if it will be execute by loop in the future. Correct me if I’m wrong.

  3. Why use Isolate when there is future? I saw some examples using Isolate for some heavy task instead of Future. But why? It only makes sense to me when future execute asynchronously on the main isolate queue.


A Future is a handle that allows you to get notified when async execution is completed.
Async execution uses the event queue and code is executed concurrently within the same thread.


Dart code is by default executed in the root isolate.

You can start up additional isolates that usually run on another thread.
An isolate can be either loaded from the same Dart code the root isolate was started with (with a different entry-point than main() https://api.dartlang.org/stable/2.0.0/dart-isolate/Isolate/spawn.html) or with different Dart code (loaded from some Dart file or URL https://api.dartlang.org/stable/2.0.0/dart-isolate/Isolate/spawnUri.html).

Isolates don’t share any state and can only communicate using message passing (SendPort/ReceivePort). Each isolate has its own event queue.


Answered By – Günter Zöchbauer

Answer Checked By – Clifford M. (FlutterFixes Volunteer)

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