Thread safe class method defined in Powershell hangs inside a Lazy inside a ConcurrentDictionary

Prerequisites

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• Make sure you are able to repro it on the latest released version
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Steps to reproduce

I have a thread safe class method (it’s static and empty) that is hanging when called inside of a System.Lazy initializer inside of a System.Collections.Concurrent.ConcurrentDictionary when used with ForEach-Object -Parallel. Calling a normal dotnet method works fine (e.g. [System.Convert]::ToString(132456, 2)), but my [Dead]::Lock() method call hangs.

This is as far as I was able to strip my repro code down while still causing the hang:

#Requires -Version 7

Write-Host "Starting job`n"

$dict = [System.Collections.Concurrent.ConcurrentDictionary[string, System.Lazy[string]]]::new()

$job = 1..16 | ForEach-Object -AsJob -ThrottleLimit 16 -Parallel {
    $threadNum = $_
    $dict = $using:dict

    class Dead {
        # This method should be thread safe(?)
        static [void] Lock() {
        }
    }

    [System.Console]::WriteLine("Starting thread #$threadNum")

    $lazy = $dict.GetOrAdd("same key", [System.Lazy[string]]::new(
        {
            # Calling this method causes the script to hang, even though it should(?) be thread safe
            [Dead]::Lock()

            $okToCall = [System.Convert]::ToString(132456, 2)
            return ""
        },
        [System.Threading.LazyThreadSafetyMode]::ExecutionAndPublication))

    [void]$lazy.Value

    [System.Console]::WriteLine("Completed thread #$threadNum")
}
try {
    while (!$job.Finished.WaitOne(1000)) {
        Write-Host "$(Get-Date): Waiting"
    }
    $job | Receive-Job

    Write-Host "`nFinished job`n"
} finally {
    $job | Stop-Job
}

Note: you may need to run this a bunch of times to actually see the hang. I’m also running this without my profile to ensure that’s not interfering: pwsh.exe -NoProfile -File $Home\OneDrive\Scripts\bug.ps1

I’ve had independent verification of the hang from at least one other user.

Expected behavior

PS C:\> pwsh.exe -NoProfile -File $Home\OneDrive\Scripts\bug.ps1
Starting job

Starting thread #1
Starting thread #2
Starting thread #3
Starting thread #4
Starting thread #5
Starting thread #6
Starting thread #7
Starting thread #8
Starting thread #9
Starting thread #10
Starting thread #11
Starting thread #12
Starting thread #13
Starting thread #14
Starting thread #15
Starting thread #16
Completed thread #2
Completed thread #6
Completed thread #9
Completed thread #13
Completed thread #3
Completed thread #1
Completed thread #4
Completed thread #5
Completed thread #7
Completed thread #8
Completed thread #10
Completed thread #11
Completed thread #12
Completed thread #14
Completed thread #15
Completed thread #16

Finished job

PS C:\>

Actual behavior

PS C:\> pwsh.exe -NoProfile -File $Home\OneDrive\Scripts\bug.ps1
Starting job

Starting thread #2
Starting thread #1
Starting thread #3
Starting thread #4
Starting thread #5
Starting thread #6
Starting thread #7
Starting thread #8
Starting thread #9
Starting thread #10
Starting thread #11
Starting thread #12
Starting thread #13
Starting thread #14
Starting thread #15
Starting thread #16
10/10/2022 11:52:52: Waiting
10/10/2022 11:52:53: Waiting
10/10/2022 11:52:54: Waiting
10/10/2022 11:52:55: Waiting
10/10/2022 11:52:56: Waiting
10/10/2022 11:52:57: Waiting
10/10/2022 11:52:58: Waiting
10/10/2022 11:52:59: Waiting
10/10/2022 11:53:00: Waiting
10/10/2022 11:53:01: Waiting
10/10/2022 11:53:02: Waiting

Error details

No response

Environment data

Name                           Value
----                           -----
PSVersion                      7.2.6
PSEdition                      Core
GitCommitId                    7.2.6
OS                             Microsoft Windows 10.0.22621
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response

[SeeminglyScience]

Thanks! I don’t think I ever would have found that existing issue. 😃

Oh yeah, you’re good, we just mark it for tracking purposes 😃 We would always much prefer duplicates over issues going unreported ❤️

Especially with issues as impossible to search for as this 😁

[SeeminglyScience]

This is a known issue (and somewhat by design) for static methods. Very recently a PR was merged adding a way to strip runspace affinity for a class. Once that makes it to a preview, that will be the recommended way of handling it.

In earlier versions you can move to instance methods and use the work around described in https://github.com/PowerShell/PowerShell/issues/3651#issuecomment-306968528