Better messaging for pause on isolate events

[keertip]

Right now Editor users have no indication that the application has paused and they should switch to the observatory to continue. For a start, it would be fine to print to stdout indicating the event and the url to reach the observatory.

[johnmccutchan]

Marked this as blocking #18358.

[kasperl]

Removed this from the 1.4 milestone.
Added this to the 1.5 milestone.

[kevmoo]

Removing the Milestone 1.5 flag. Please yell loudly this is critical for 1.5.

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cc @keertip.
Removed this from the 1.5 milestone.

[iposva-google]

Printing to stdout will change the program's behaviour. So that is not an option.

The editor can make an observatory request and verify whether the isolate is running or paused showing an indication if that is desired.

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cc @johnmccutchan.
Removed the owner.
Removed Area-Observatory label.
Added Area-Editor label.

[kasperl]

Added this to the 1.6 milestone.

[clayberg]

Set owner to @keertip.
Removed Type-Defect label.
Added Type-Enhancement label.

[keertip]

John,

The editor is using the --trace_service_pause_events when starting the observatory. I see a message in the console like the one below for pause isolates on exit, but not for pause isolates on start. Is the editor missing the message or does the observatory not show it?

Isolate sample.dart$main-518862436 paused before exiting. Use the Observatory to release it.

[johnmccutchan]

Hi,

We don't display any message when paused on start. We probably shouldn't print anything but have the editor poll over the VM service for status changes in isolates- it's really simple and could provide a better user experience.

John

[keertip]

What would this involve? And how would the editor use the status info to provide a better user experience?

[johnmccutchan]

Hi,

It would involve polling (with an HTTP request) the service port checking on the status of isolates. It's possible to tell if an isolate is blocked before starting or blocked from exiting (among many other things). I'm no UI/UX expert though it just seems better to have the Editor actually know what's going on and surface that data to the user in a way other than having it show up console output. Possibly, the better UI would be to bring up a dialog box or modify the debugger tool to reflect this state. I think burying this in the console output isn't very discoverable.

[keertip]

The polling looks like a bit of work for the editor. For now will go with adding a message to indicate pause on start. And we have a message to indicate pause before exit.

https://codereview.chromium.org/387283002/

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Added Fixed label.