VS2017 RC2 intellisense blocks the GUI

[gusty]

I've tested editing projects like FSharpPlus which makes heavy use of overload resolution, with the new Visual Studio 2017 and found that now it seems that the UI is blocked until intellisense finish inferring the types.

Since overload resolution time was improved this is not a big issue, I prefer it to the old Visual Studio but each time the code is edited the whole UI is blocked for a few seconds in my computer which is not very fast.

Repro steps

1. Open FSharpPlus

2. Go to a file, like operators.fs and rename a function.

Expected behavior

The GUI continues working while type inference works on the background.

Actual behavior

The GUI is blocked. Scroll bars, cursor, everything freezes for a very few seconds.

Known workarounds

I don't know any interesting workaround at the moment.

Related information

• Operating system: Windows 10 Pro N
• Branch: RC2
• .NET Runtime, CoreCLR or Mono Version: 4.6.01586
• Editing Tools (e.g. Visual Studio Version): 2017 RC2
• Links to F# RFCs or entries on http://fslang.uservoice.com: N/A
• Links to performance testing scripts: N/A
• Indications of severity: Medium to High

[vasily-kirichenko]

See #1825, in short, it's fixed on roslyn side, we will check if the fix works as new roslyn nuget published.

[gusty]

Thanks, but are you sure it's the same issue?
That issue is with CTRL+SPACE, I've seen problems with that long before VS 2017, I remember once I had to restart my PC and lost the work.
Otherwise let's wait until the nuget is published.

[vasily-kirichenko]

Ah, sorry, I read the issue not carefully enough. If you have UI freezes during code editing (no intellisense involved), than check devenv.exe process private set. If it exceeds 2GB, nothing can help - blocking GC kills UI. Restart VS is the only way to fix this. However, on the compiler project you reach 2GB very quickly. The cause are FSC caches, I've no idea how to reduce their memory appetite.

[gusty]

Also that issue, I think, is a different issue. I see the memory of devenv.exe around 225 MB.
If you don't have a superfast computer you can try open a code file on that project, you will see the freeze as soon as you open it, it freezes for a short time until it colours the code, them each time you edit something freezes again.

[vasily-kirichenko]

We use Roslyn API for everything, including colorizing, error/warning reporting, etc. That API is fully asynchronous, I mean all the methods we implemented return Task<...>. So, if there are UI freezes they are rooted to Roslyn itself.

Could you please profile VS with dotTrace in its "Timeline" mode? It will show UI freezes explicitly, like this:

[vasily-kirichenko]

@gmpl I cannot build FSharpPlus:

Looks like you don't use FSharp.Core NuGet package:

I don't have VS 2013 / F# 3.1-4.0 installed.

[vasily-kirichenko]

I cannot reproduce it:

[gusty]

Yes, the build was broken but now it's fine.
It seems it works fine for you.
I will see if there is an update for the VS.

[vasily-kirichenko]

This is the version info:

I have a fairly fast machine (i7-4790K at 4GHz). However, I don't experience any freezes or delays, even sub second ones.

[gusty]

Hmmm, it's the same VS version I have.
It definitely works fine for you from what I can see in your video.
I do have VS2015 installed on the same OS.

[vasily-kirichenko]

I have no more ideas but a suggestion to profile VS with dotTrace.

[gusty]

Yes, that's exactly what I'm looking for.
It might give us more precise information.

[gusty]

After installing dotTrace I found the Timeline option but don't get to that screen.
Could you explain me the steps to get to the window with UI freezes?
Thanks

[cartermp]

I can't repro this either. Type colorization is a bit slow on some of the larger files (as I would expect), but I don't notice any UI blockage. As @vasily-kirichenko mentioned, every editor API that we implement is asynchronous, with the exception of completions via ctrl-space (and that's actually been changed by the Roslyn team to allow for asynchrony).

Hopefully we can figure out why this is happening on your machine.

[vasily-kirichenko]

@gmpl