Poor error handling in Dartium isolates

[peter-ahe-google]

Consider this program:

import 'dart:isolate';
import 'dart:html' show HttpRequest;

useHttpRequest() {
  print('In isolate.');
  HttpRequest.getString('test.dart').then((text) => print(text));
}

main() {
  print('Starting isolate');
  spawnFunction(useHttpRequest);
}

All that shows up in the console is:

"Starting isolate undefined:1"

I had expected to see:

"Starting isolate test.dart:10
[From isolate] In isolate. test.dart:5
[From isolate] DOM access is not enabled in this isolate

­0 HttpRequest._create (file:///Volumes/data/b/build/slave/dartium-mac-inc/build/src/out/Release/gen/webkit/bindings/dart/dart/html/HttpRequest.dart:60:3)

­1 HttpRequest.HttpRequest (file:///Volumes/data/b/build/slave/dartium-mac-inc/build/src/out/Release/gen/webkit/bindings/dart/dart/html/HttpRequest.dart:58:35)

­2 HttpRequest.request (file:///Volumes/data/b/build/slave/dartium-mac-inc/build/src/out/Release/gen/webkit/bindings/dart/dart/html/HttpRequest.dart:10:15)

­3 HttpRequest.getString (file:///Volumes/data/b/build/slave/dartium-mac-inc/build/src/out/Release/gen/webkit/bindings/dart/dart/html/HttpRequest.dart:5:19)

­4 useHttpRequest (http://127.0.0.1:56653/web_editor/test.dart:6:26)

This is almost what happens if I modify useHttpRequest:

useHttpRequest() {
  print('In isolate.');
  try {
    HttpRequest.getString('test.dart').then((text) => print(text));
  } catch (e, trace) {
    print('$e\n$trace');
  }
}

So the following questions arise:

1. Why isn't the the text "In isolate" printed in the console?
2. Why isn't the uncaught exception diagnosed?
3. Why doesn't the debugger pause on the exception?
4. Why does the console say "undefined:1"?

I'll file a separate bug about HttpRequest not being available.

[DartBot]

This comment was originally written by [email protected]

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1. Why isn't the the text "In isolate" printed in the console?

Corner case of the implementation: child isolate dies too early. Please, file a separate bug.

1. Why isn't the uncaught exception diagnosed?

Please, file a separate bug.

1. Why doesn't the debugger pause on the exception?

I don't think it's a default behaviour for JS in Chromium.

1. Why does the console say "undefined:1"?

See https://code.google.com/p/dart/issues/detail?id=5851

[peter-ahe-google]

I'm sorry, but the experience totally sucks, that is the topic of this bug. If you need to divide the work into several issues, please do so.

As far as I can tell, there is no way to get the debugger to pause on exceptions in isolates. Even setting a breakpoint has no effect.

FWIW, the JS chrome behavior for web workers is also horrible. I hope we set the bar higher in Dart. But it is at least possible to get JS/chrome to break on all exceptions in workers.

[DartBot]

This comment was originally written by [email protected]

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Added this to the Later milestone.

[kasperl]

Removed this from the Later milestone.
Added Oldschool-Milestone-Later label.

[kasperl]

Removed Oldschool-Milestone-Later label.