Fetch the extension registry again when delegate command handler not found

[jdneo]

• fetch the extension registry again when delegate command handler cannot be found.
• change WorkspaceExecuteCommandHandler to Bill Pugh Singleton (thread safe).

Background

Our extension's BI shows that there are some no delegateCommandHandler errors. It's hard to stably reproduce but looking into the code, looks that we have some issues under the concurrent scenarios.

For example, when a command starts to find its delegator before it's added via public synchronized void added(IExtension[] extensions).

This case can be easily reproduced in debug mode:

1. set a break point in the entry of public synchronized void added(IExtension[] extensions)
2. Launch JDT.LS and open https://github.com/spring-projects/spring-petclinic/blob/main/src/main/java/org/springframework/samples/petclinic/PetClinicApplication.java
3. There are some chances that the local cache is out-of-sync (the variable candidates is empty after filtering), since the breakpoint postpone the handler registration into the cache.

Signed-off-by: Sheng Chen sheche@microsoft.com

[rgrunber]

I wasn't able to get added(..) to trigger, but I suppose if the set of candidates really is empty, it couldn't hurt to try re-loading.

[rgrunber]

@jdneo , was this fix likely a result of microsoft/vscode#161563 ? I'm guessing that was the root cause.

[jdneo]

Yes, we did some tests about the bundle registration recently, and found that the root cause is that some bundle file locations are not sent from client to server at the beginning (extension.all does not contain those extensions at first, those missing extensions are discovered later by VS Code).

If we want to address this on our side, a possible solution might be when the client received an extension did change event, send some kind of refresh bundle request to the server. This means the server will allow to install bundles not only in the initialization phase, but anytime actually. (One more benefit is that we may say goodbye to reloading VS Code when new Java extension is installed)