Sending text to FSI is very slow

[SchlenkR]

Sending text to fsi (can be strings or just code in general) takes a very long time compared to Rider or Visual Studio. You can see the behaviour here:

When sending larger sources to FSI, this can be very annoying and it lowers the "working with data in F#" experience drastically. I don't know where exactly this is coming from. What I can tell is that it makes my use cases almost unusable - sometimes output is even slower than shown in the GIF. This behaviour can also be seen when you run things like this:

seq {
    for x in 1..5000 do "test"
}
|> String.concat " "

...or when you display a response from a webserver.

When I simply send text to a vi (bash) in vscode, the text is displayed immediately.

I know that there was an issue like that here, but I don't find it anymore.

If I can assist you somehow, please let me know.

Hint: This is independent from the usage of .Net 5 preview / .Net 461 / .Net Core version.

• Operating system: Windows_NT
• Arch: x64
• VSCode: 1.48.2
• Runtime: netcore
• Dotnet version: 5.0.100-preview.8.20417.9
• MSBuild version:

Microsoft (R)-Build-Engine, Version 15.9.21+g9802d43bc3 f�r .NET Framework
Copyright (C) Microsoft Corporation. Alle Rechte vorbehalten.

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[Krzysztof-Cieslak]

TBF, not sure if we have any impact on this - we just call "send a text to terminal" API from VSCode

Maybe @Tyriar can help us with this?

[Tyriar]

We made a change recently to fix a long standing issue where sent/pasted text would be truncated microsoft/vscode#38137. The fix was to split up the text into chunks of 50 characters which seems to match your gif.

I think now you're hitting a known Windows perf problem as a result of running conpty on the UI thread which is tracked in microsoft/vscode#74620

[isaacabraham]

I saw this and tried moving back to the standard terminal renderer - for some reason I was on the DOM one which was super slow.

[SchlenkR]

I guess it might really be a windows issue. When I send a bunch of text via the "Terminal: Run Selected Text in Active Terminal" to a Windows Powershell Terminal, it is also quite slow (like in the gif above).

Now when I run bash -c “vi filename.txt” and send the same text to it, it is really fast.

[isaacabraham]

@ronaldschlenker which terminal renderer are you using?

[SchlenkR]

I tried it with all 3 (canvas, dom and WebGL), but there is no significant difference. And I think the issue has definitely something to do with the used console host and maybe the communication with it, since using WSL/bash, it is really fast.

[Krzysztof-Cieslak]

Ok, I'm closing this one here, as it's nothing we can control/fix anyway.