Deactivating extensions do not always have enough time to clean up

[MSLaguana]

• VSCode Version: 1.5.1
• OS Version: Windows 10

Steps to Reproduce:

1. Check out https://github.com/MSLaguana/vscode_deactivate_process_issue
2. Run the extension in that project
3. In the command palette, run "Spawn child process"
4. Navigate to localhost:8080 and verify that a webserver is running
5. In the command palette, run "Kill child process"
6. Navigate to localhost:8080 and verify that no webserver is running; the cleanup command works correctly.
7. In the command palette, run "Spawn child process", then close the experimental vscode instance
8. Navigate to localhost:8080 and verify that the webserver is still running

We ran into this issue at microsoft/vscode-react-native#300 where during normal usage of the extension, we start a long-running child process which we want to clean up when the extension stops.

Specifically we are trying to run child_process.spawn("react-native.cmd", ...), which ends up creating an instance of cmd /c react-native.cmd that in turn creates the desired node cli.js .... We would like to make sure that descendant process is cleaned up, but because there is an extra layer of indirection we cannot simply call child_proc.kill() since that kills the cmd process but not the node process.

To work around this, on windows we use taskkill /T to kill the cmd process and all its descendants. This works fine during normal operation, but when the extension is terminating invoking taskkill is an async exec operation and so it does not complete. I also tried using exec-sync but that didn't help either.

Any suggestions on how to improve our behaviour here instead of leaking processes?

[alexdima]

Apologies for not answering here sooner, the deactivate method can return a promise and the extension host process will self-destruct when all the deactivate promises have completed or when 4 seconds have elapsed, whichever happens first.