How should i use Dart Isolate unhandledExceptionCallback?

Question

I'm trying to use Isolates in my Dart webapp but i can't seem to make the error callback argument work. I have a very basic code which is being run in Dartium.

import "dart:isolate";

void main() {
  print("Main.");
  spawnFunction(test, (IsolateUnhandledException e) {
    print(e);
  });
}

void test() {
  throw "Ooops.";
}

I never see anything than "Main." printed on the console. Am i doing something wrong or is this broken right now?

Then what's the easiest way to catch and log messages from an Isolate right now? Isolates can't access DOM nor print to the console. I don't know if exceptions are serializable on a stream because in that case i can send them to the host code using a MessageBox and the streamSpawnFunction variant and print them there. But this is ugly as hell :( — NagyI, Mar 23 '13 at 13:32
Okay this works but it's till very ugly :) I might write a wrapper Isolate class on my own. I need bidirectional communication anyway which already requires some helper code. I don't know why was it good to remove the Isolate class from earlier Dart versions anyway. It's a lot more confusing to recreate the streams on my own. — NagyI, Mar 23 '13 at 14:22

score 2 · Accepted Answer · edited Oct 06 '14 at 10:54

The error-callback will be executed in the new isolate. Therefore it cannot be a dynamic closure but needs to be a static function.

I haven't tested it, but this should work:

import "dart:isolate";

bool errorHandler(IsolateUnhandledException e) {
  print(e);
  return true;
}

void test() {
  throw "Ooops.";
}

void main() {
  // Make sure the program doesn't terminate immediately by keeping a
  // ReceivePort open. It will never stop now, but at least you should
  // see the error in the other isolate now.
  var port = new ReceivePort();
  print("Main.");
  spawnFunction(test, errorHandler);
}

Note: In dart2js this feature is still unimplemented. Older versions just ignored the argument. Newer versions will throw with an UnimplementedError.

How should i use Dart Isolate unhandledExceptionCallback?

1 Answers1