VM service does not hot reload non-main Isolates

[maks]

Using the vm service package it should be possible to use the reloadSources to hot reload an Isolate from changes made to the src file on disk.

With current master of the Dart SDK this seems to work fine using the DartVM in JIT mode on the commandline with the main isolate but not with any isolate's spawned from the main isolate.

This seems to have been reported in several different Flutter issues:

• Hot reloaded changes are not applied to new isolates as they are launched flutter/flutter#18600
• Hot Reload does not update background isolate flutter/flutter#20743

This was supposedly fixed for Flutter in this change as part of flutter/flutter#52149 but I don't see how that could actually be working at the moment as I am seeing that it doesn't work with just the standalone Dart SDK.

I created a modified version of the recharge package that demonstrates this issue.

To reproduce:

1. clone the above repo and use the background-isolate-test branch, run: dart --enable-vm-service example/hello.dart
2. edit hello.dart changing the value returned by mesg() and the print inside worker()
3. note the pid printed out from step 1 and send it a sigusr1, eg kill -n 10 <pid-of-example>
4. notice that the output will show the new value of mesg() but NOT of the worker's print()

The version I have been testing with is built locally:

dart --version
Dart SDK version: 2.12.0-edge.30c4006d52fad4ee8b92025933b9f17af7a8740f (be) (Thu Dec 31 00:48:50 2020 +0000) on "linux_x64"

[mkustermann]

This is due to #36648. We intend to solve as part of #36097

[aam]

Just to clarify - the issue demonstrated above with recharge package is not that non-main isolates are not hot-reloaded, rather that after a hot-reload, isolates spawned after_that(worker isolate in the repro above) don't have that hot-reload updates, instead spawned with the original source.

[gnprice]

This is due to #36648. We intend to solve as part of #36097

Those two issues have been resolved. I just tried the repro recipe above, and confirmed that it no longer reproduces — at step 4, I see the new version of both strings.

That's with:

$ dart --version
Dart SDK version: 2.18.6 (stable) (Unknown timestamp) on "linux_x64"

So I believe this issue can be closed.

[maks]

yes sorry I forgot about this issue.
I just retested myself with 2.18.6 on linux and concur its now fixed so I'll close this now.