VS 2019 16.0.0 RC.3/Preview 4.3 freezes frequently when Intellisense active while editing F#

[BentTranberg]

I updated to VS 2019 Preview 4.3, and also installed the corresponding RC.3. They both permanently froze (hung) typically only a minute or two into editing, so I could not really get much work done.

I turned off the status bar, because I suspected it could be related to issue #6335 that I opened a few days ago. It didn't help, which makes sense, because this behaves differently. There could be some behavioral pattern while I edit, but if so I haven't noticed what it is.

Just like in issue #6335, when the freeze occurs, there is a message in the status bar that reads "Locating the symbol under the caret...". This makes me think Intellisense is involved, so in the Error List pane I changed from "Build + Intellisense" to "Build Only". I have not had any freezes after that.

I do not know if this issue belongs here or in some other repo. I mostly work with F# and XAML - very little C# (minimal code behind) and no VB. In earlier previews (edit: and now also once in this latest) I've had freezes while working with XAML. I have not tried reproducing this issue while editing other code than F#.

[Pilchie]

@TIHan @cartermp ping - can you work with @BentTranberg to get a trace to look at?

[TIHan]

Hey @BentTranberg , thank you for testing and reporting. There are a couple of things you can do:

If it freezes again, you can try ProcDump, https://docs.microsoft.com/en-us/sysinternals/downloads/procdump, on the devenv.exe process - more info on minidumps: https://www.wintellect.com/how-to-capture-a-minidump-let-me-count-the-ways/

Also, you can use this reg file, https://github.com/dotnet/project-system/blob/master/docs/repo/content/AlwaysSaveDevEnvCrashDumps.reg that will automatically save crash dumps if you get any crashes. This one may not be useful for this scenario, but it's probably a good idea to have it just in case.

[BentTranberg]

I have no experience with ProcDump. I see that I can run procdump devenv.exe devenv.dmp and get a dump file when VS is ok, but I also see there's a parameter -h for hung processes. It looks like it just waits for VS to get hung then. I can't easily test what will produce a dump on a hung VS at the moment, because on my home computer I don't have these hangs frequently enough. I'll be back at work in around 10 hours, and then I guess I'll have some results pretty quickly. I also use that reg-file.

[TIHan]

Take your time. Let me know if you have more questions.

[penguid]

I have also experienced freezes while editing F# code in RC.3. Occurs even with status bar turned off.

It has occurred both:

1. With a "Please wait for an editor command to finish..." dialog whose Cancel button does not respond to input.
2. Without a dialog.

I have taken procdumps of both occurrences. They are about 40 MB files. Let me know if I should do anything with them.

[BentTranberg]

I switched back to "Build + IntelliSense" in the Error List on my computer at work this morning, and in spite of that haven't had a single freeze/hang today - around 6 hours editing.

With my limited knowledge, the only possible cause for this that I can think of is that files in the .vs, bin and obj folders can perhaps cause problems when updating VS. Eventually old files will be overwritten, and problems go away. I've experienced that more than once or twice during the years I've been using VS. Not saying this is likely - only a possibility.

ps: I did notice that hangs was considerably less frequent towards the end of the day yesterday, when I tried with IntelliSense.

[TIHan]

@penguid You could send the dumps over our way if they don't contain anything what would have to be under NDA, I just don't know where you should upload it. I'll ask around.

@BentTranberg The seems interesting. This is basically what happened to another dev. The first time they used it, it froze, but after that it never froze again, even after 3 weeks of usage.

[BentTranberg]

Next time somebody experiences this, it might be a good idea to create a backup of not just the source, but also the binaries in .vs, obj and bin. (Any other folders of interest?) Based on what little we know so far, that might give a better chance of reproducing the problem more consistently and ad infinitum for research.

And again, my notion could easily be totally wrong, so it's just a suggestion if there's a lack of other ideas.

On the bright side, I'm happy the problem is gone on both my development computers now. I am thinking perhaps checking out a clean working copy is an instant workaround slash fix with no drawbacks.

[penguid]

@TIHan Here is a project that repros fairly consistently on my system even with fresh clone: https://github.com/penguid/vs2019rcfreeze

1. Open Server3.sln
2. Open Giraffe3\Json.fs
3. Click on okRaw identifier (line 12)
4. Press CTRL+ENTER -- usually freezes here

If no freeze right away, click around on different identifiers and occasionally hit CTRL+ENTER and CTRL+L to add and delete lines. Try other files too. If no repro within a couple minutes, close VS and start over.

If you/others can't repro then I can send the dumps, no NDA concerns but preferably somewhere private as I don't know what personal info is in there.

[cartermp]

@penguid I can't speak for the status bar setting, but that sounds like the root issue in #6335

ctrl when the caret is over a symbol will asynchronously find its definition so that when you click on the identifier, it will go to definition. This process posts a message to the VS status bar service saying it is navigating to the definition of the symbol. Due to an issue in the status bar service, this can cause VS to deadlock. #6339 disables all our message posting to just be no-ops, so it should resolve what you have said.

Do you see this under any circumstances when ctrl is not pressed or held down? If so, that would indicate a different issue also occuring.

[cartermp]

@penguid Can you confirm that you turned this setting off and restarted VS? I can reproduce your freeze as described if it is on, but if I turn it off I cannot reproduce it. I also cleared the .vs folder, forcing a first-time solution load where I first saw it.

[penguid]

@cartermp Offhand I don't recall it occurring without using ctrl key (but I wasn't paying much attention at first so I can't say for certain).

[penguid]

@cartermp Yep it is off and restarted (normal restart, not via killing a hung process). To double check, I just now: turned it on, restarted normally, turned it off, restarted normally, verified the setting was off, then tried my repro steps. After two more normal restarts where it didn't repro, a third restart resulted in another repro, with the setting off.

[BentTranberg]

Finally got a hang. I'm learning Hopac from scratch this weekend, so this is a very small sample application I just got started, which is ideal for a repro. I was pasting in some more sample code from the web to Lesson1.fs, started to prettify the pasted source, and then VS froze. Then I ran this: procdump.exe devenv.exe vs2019.dmp

TestHopac.zip - contains the source and folders .vs, bin and obj. I included the three extra folders in case they can provide any clues.
vs2019.dmp - sent as zip partitions zipped. Explanation follows.

To get around the 10 meg limit on GitHub, I used 7z to zip vs2019.dmp into partitions. Then I zipped each partition into a zip again, because the number file extensions are not accepted by GitHub. If there is a better way you want me to use to transfer the dump file, let me know.

TestHopac.zip
vs2019.zip.001.zip
vs2019.zip.002.zip
vs2019.zip.003.zip
vs2019.zip.004.zip

[BentTranberg]

Instructions for reproducing hang with repro TestHopac.zip.

In file Lesson1.fs, the goal is to add another module at the end. This module should look like this.

module Lesson1d =

    type Product = { Id: int; Name: string }

    let getProduct id = job {
        do! timeOutMillis 2000 // Delay in the place of DB query logic for brevity
        return {Id = id; Name = "My Awesome Product"}
    }

    type Review = { ProductId: int; Author: string; Comment: string }

    let getProductReviews id = job {
        do! timeOutMillis 3000 // Delay in the place of an external HTTP API call
        return [
            {ProductId = id; Author = "John"; Comment = "It's awesome!"}
            {ProductId = id; Author = "Sam"; Comment = "Great product"}
            ]
        }

I am pasting the code within the module from this page, from the two boxes below the headline "A Real World Example" : https://www.demystifyfp.com/fsharp/blog/concurrent-programming-in-fsharp-using-hopac-part-1/

As you can see, the original code is not formatted in the style I want, and with the indents I need. It is when I try to paste from the boxes and then start to manually reformat (prettify) the code, that VS hangs at some point.

Copy from the first box on the web page, then paste, and then manually reformat. Then do the same with the code from the second box on the web page.

I can see from repeatedly trying, that VS hangs at certain points in my editing routine, and I suspect it is always when I edit inside the brackets of the two types.

Manually editing in Notepad, and then pasting, is a workaround.

Oh, and I took a few more dumps, in case they're needed. (Hmmm ... that doesn't sound right.)