Will Dart execute isolates in parallel in a multi-core environment?

Issue

Question

Will isolates in Dart run in parallel utilizing all available cores on a multiple core environment, or will it multiplex on a single core?

Background

Google has described isolates (a single-threaded unit of concurrency) in the Dart programming language as a "light weight thread" that operates on the main stack, without blocking.

Thus, it seems to me as it will only be able to multiplex on a single core and not be able to run in parallel over multiple cores in a SMP, dualcore, multicore or clustered environment.

Though, I can’t find any information on this, hence my humble question.

Solution

Warning: the code below is out of date and does not work with Dart 1.0.

Short answer

Maybe.

Long Answer

The dart:isolate library guide states: “Isolates might run in a separate process or thread, depending on the implementation. For web applications, isolates can be compiled to Web workers, if they are available.” (my emphasis)

Running this code and observing your CPU load will tell you if your implementation does this or not.

#import('dart:isolate');
main() {
  for (var tmp = 0; tmp < 5; ++tmp) {
    SendPort sendPort = spawnFunction(runInIsolate);
    sendPort.call(tmp).then((reply) {
      print(reply);
    });
  }
}

runInIsolate() {
  port.receive((msg, SendPort reply) {
    var k = 0;
    var max = (5 - msg) * 100000000; 
    for (var i = 0; i < max; ++i) {
        i = ++i - 1;
        k = i;
    }
    reply.send("I received: $msg and calculated $k");
  });
}

The standalone dartvm will run isolates in parallel, utilizing all available cores. Browser implementations of Dart will likely vary depending on whether Web Workers are implemented or not.

Answered By – Aron Cederholm

Answer Checked By – Candace Johnson (FlutterFixes Volunteer)