Dart Isolates As Workers

Issue

Edited to make the question more clear.

I am trying to work with Isolates (or Web Workers) in Dart. The only ways I can find to communicate between the main and isolate threads are send and call & then from the main thread. But that’s a nice way for the main thread to pass some data to the isolate.

What’s if I want the isolate to be the one who generates information? Like a game engine that does all the physics in a worker and then sends an updated world information to the main thread? In JavaScript you can send data at any time. Is there an efficient way in Dart? Or do I still have to wait for the main thread to call me and then pass it to it?

P.S. I wonder, does call & then block the thread until reply is done or not?

Solution

WARNING: this code only works on very old versions of Dart. It does not work on Dart 1.0 or later.

As you mention to post messages to a isolate you need to have a handle on it’s sendport.

#import('dart:isolate');

main() {
  SendPort sendPort = spawnFunction(doWork);
  sendPort.call("hey 1").then((String res) => print("result was: [$res]"));
  sendPort.call("hey 2").then((String res) => print("result was: [$res]"));
}

doWork() {
  port.receive((msg, reply) {
    msg = "msg $msg";
    reply.send(msg);
  });
}

however since the Dart main thread is itself an isolate you can send data to it by using the global port function:

#import('dart:isolate');
#import('dart:io');

main() {
   port.receive((data, reply) {
       // in here you can access objects created in the main thread
       print("handle [${data['text']}] for index ${data['index']}");
   });

   SendPort workPort = spawnFunction(doWork);
   workPort.send("msg", port.toSendPort());
}

doWork() {
   port.receive((msg, reply) {
      int i = 0;
      new Timer.repeating(1000, (Timer timer) {
         i++;
         var data = {
            "text": "$msg $i",
            "index": i
         };
         print("sending $data");
         reply.send(data);
      });
   });
}

Note there are certain limits about what can be send back and forth between isolates and also currently isolates act differently in JS and on the VM. The current limitations are well described here.

Answered By – Lars Tackmann

Answer Checked By – Cary Denson (FlutterFixes Admin)