fix #3697 Remove blocking await.

[caseyflynn-google]

PR removes blocking await when starting a file watcher. This is
particularly important when starting Theia with a large workspace root
as the file watch will block Theia loading.

Signed-off-by: Casey Flynn caseyflynn@google.com

[akosyakov]

PR removes blocking await when starting a file watcher.

I wonder how await can be blocking. Blocking code usually is synchronous and does not allow node process to handle new requests. In this case, the code seems to be async and should allow handling of other requests.

[paul-marechal]

@akosyakov you are right that an await allow for non blocking code, unless something in the Theia boot-up sequence someone specifically wait for this before starting the application. Somewhere inside a onStart hook?

root WARN EditorNavigationContribution.onStart is slow, took: 46547 ms

When I opened Theia on /.

[akosyakov]

@marechal-p can you profile the frontend please and find out with the root cause why it takes 45s? We need to rewrite EditorNavigationContribution for sure, that it does not block the shell to load navigation history: #3413 But I suspect it is not related to this issue or a follow-up effect.

I am also not against these changes. I want to understand why it helps and how I can verify it + unwatch should be handled properly.

[paul-marechal]

@akosyakov the long wait is because of something silly:

EditorNavigationContribution.onStart needs to call some WorkspaceStorageSerivce.getData which will wait for WorkspaceStorageService to be "initialiazed", that happens when the WorkspaceService has resolved its roots. But somewhere in the root resolution, there was an await on the watchers.

I made a diff to see if I could fix it where the wrong components were waiting for it: 7bb1e9b

With this, the EditorNavigationContribution.onStart goes from [10 to 50] seconds down to ~400ms, when opening my system root (/)

[caseyflynn-google]

With this, the EditorNavigationContribution.onStart goes from [10 to 50] seconds down to ~400ms, when opening my system root (/)

This seems to resolve the issue for me too. Can we apply this fix to Master?

[akosyakov]

@marechal-p thanks for the analysis, it is clear now

@caseyflynn-google as soon as tests are green

I've pushed one commit to address https://github.com/theia-ide/theia/pull/3699/files#r238060287 The await was there to make sure that the disposable object for a watcher is created. If we remove await we need to create this object earlier. I've pulled it up.