Dart's isolate test

isolate-test.dart

class Printer extends Isolate {
  main() {
    port.receive((message, replyTo) {
      if (message == null) port.close();
      else print(message);
    });
  }
}

main() {
  // first isolate process
  new Printer().spawn().then((port) {
    for (var message in ['Hello', 'from', 'other', 'isolate']) {
      port.send(message);  
    }
    port.send(null);
  });

  // second isolate process
  new Printer().spawn().then((port) {
    for (var message in ['*Hello', '*from', '*other', '*isolate']) {
      port.send(message);  
    }
    port.send(null);
  });
}

// Results (WTF?)

Hello
from
other
isolate
*Hello
*from
*other
*isolate

// Why the output is sequential but not parallel? How the Dart's processes' scheduler work?

This is outside the scope of the current conversation regarding light and heavy isolates. My question is more basic; the syntax is confusing me. What exactly are we passing in as an argument to "then"? I think mostly "(port)" is throwing me off.

new Printer().spawn().then((port) {
for (var message in ['Hello', 'from', 'other', 'isolate']) {
port.send(message);
}
port.send(null);
});

Ahh I see now that its an anonymous function, so once the Isolate is spawned the unnamed functions is called with port as the argument.

http://www.dartlang.org/articles/idiomatic-dart/

This makes no sense. spawn indicates there's an internal scheduler involved, which would make me believe the loops run in parallel causing results not to be in a sequence.

FreakTheMighty, right, it's an anonymous callback function.

kaisellgren, yes, the same I thought (after programming in Erlang and having implemented similar scheduled processes in JS with yield -- https://gist.github.com/1127536). However, after analyzing the source code of Dart's runtime library, I figured out that it's a design decision caused by impossibility of implementation of such parallel processes with using just setTimeout scheduling (you may check btw, my similar setTimeout processes -- https://gist.github.com/1103751). That is, callback process function should run to completeness and can't be interrupted in the middle. And exactly this cases sequential execution, but not parallel.

Recently I discussed the topic in Dart's mailing list: http://bit.ly/n3IUiT

@DmitrySoshnikov: as far as I know, most ES engines do not support yield, except *Monkey. Therefore, I also believe the Dart engineers decided it is not possible to support "parallel processes" in transcompiled JS and this is the outcome :(. By the way, I like https://gist.github.com/1127536, did something similar once as well :)