Isolate vs thread

Learn the difference between isolates and threads.

Isolate vs thread

In classic languages threads share memory; this requires lock, mutex, condition variable and similar tools. Mistakes easily become race conditions.

In Dart, isolates do not share memory. Each isolate owns its stack and objects. Data is copied as a message.

Result: Dart needs no locks, but pays a copy cost. Spawning an isolate is expensive for small work; use it only for genuinely heavy work.

When to use an isolate?

Good use: CPU-heavy work taking more than 50 ms — JSON parsing, image processing, file scanning. Keeping these on the main isolate freezes the UI.

Bad use: 5 ms computations. The isolate spawn cost (copy + scheduling) exceeds the work itself. Plain synchronous code is enough.

I/O waiting (network, disk) needs no isolate; Future and async/await suffice. Isolates are for CPU work.

Exercise Run heavy work with Isolate.run

Define int kareToplam(int n) that returns the sum of squares from 1 to n. Make main async; add var result = await Isolate.run(() => kareToplam(100)); and print(result);.

Show example solution

import 'dart:isolate';

int kareToplam(int n) {
  var t = 0;
  for (var i = 1; i <= n; i++) {
    t += i * i;
  }
  return t;
}

void main() async {
  var result = await Isolate.run(() => kareToplam(100));
  print(result);
}

Test yourself

Which tool is not needed?

Isolates do not need ____.

Show answer

Isolates do not need lock.

Comparison table

Thread

Shares memory
Isolate

Does not share memory
Lock

Needed in threads
Message

Transfer in isolates
When is spawning an isolate pointless?
- A 5 ms addition
- Resizing a 4K image
- Parsing 10 MB of JSON
- Reading a 10k-row CSV
Show answer

A 5 ms addition — for 5 ms work the spawn cost exceeds the work itself.

Next lesson: Summary - Isolates

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