Garbage collection with COM objects in powershell

Question

I've created the following function for use cleaning up all references to com objects at the end of a script:

function TrashCompactor ($reflist) {

foreach ($ref in $Reflist){



[System.Runtime.InteropServices.Marshal]::ReleaseComObject([System.__ComObject]$ref) | out-null

[Runtime.InteropServices.Marshal]::FinalReleaseComObject($ref) | out-null

Remove-Variable $ref | out-null

}


[System.GC]::Collect()
[System.GC]::WaitForPendingFinalizers()

}

Will Remove-variable work as I expected? Is there any harm to including [System.GC]::Collect()?

There is no point in calling Remove-Variable inside a function on a local variable such as $ref, because it will go out of scope automatically when the function is exited; aside from that, you have to pass the name of the variable (ref), not its value ($ref) - ergo: Remove-Variable $ref; also, Remove-Variable never produces (success) output, so there's no point in piping it to Out-Null. — mklement0
– mklement0, Commented Mar 7, 2020 at 4:19

postanote · Accepted Answer · 2020-03-03 03:49:36Z

Yes, and no... as this...

[System.GC]::Collect()
[System.GC]::WaitForPendingFinalizers()

... is a common and best practice.

Windows will always do a cleanup, but it's always clean up your environment when you are done.

As documented...

Clean Up Your PowerShell Environment by Tracking Variable Use https://devblogs.microsoft.com/scripting/clean-up-your-powershell-environment-by-tracking-variable-use

And covered by this SO Q&A and accepted answer...

PowerShell release COM object

function Release-Ref ($ref) {

[System.Runtime.InteropServices.Marshal]::ReleaseComObject([System.__ComObject]$ref) | out-null
[System.GC]::Collect()
[System.GC]::WaitForPendingFinalizers()

}
because I've noted that my comobject always stay alive, I think Powershell 2.0 is not able to remove comobject no more used.

[System.Runtime.InteropServices.Marshal]::ReleaseComObject( $ref )

and that SO is exactly what you are asking, so this question is really a duplicate.

My example, I use a prefix to my variable so they are easy to find and simple globally clean up.

# Assign results to a variable and output to the screen using variable squeezing
($ponMyShell = New-Object -com "Wscript.Shell")
($ponDate = Get-Date)
($ponProcess = Get-Process |
    Select -First 3)

<#
# Results

Monday, 2 March, 2020 19:40:47

Handles  NPM(K)    PM(K)      WS(K)     CPU(s)     Id  SI ProcessName                                                                                                              
-------  ------    -----      -----     ------     --  -- -----------                                                                                                              
    186      14     2648       6800       0.14  15336   0 aesm_service                                                                                                             
    465      27    24300      34064       0.33  27612  22 ApplicationFrameHost                                                                                                     
    158       8     1928       4848       0.02  14268   0 AppVShNotify 

SpecialFolders     CurrentDirectory   
--------------     ----------------   
System.__ComObject C:\Windows\system32
#>

Get-Variable -Name 'pon*'
<#
# Results 

Name                           Value                                                                                                                                               
----                           -----                                                                                                                                               
ponDate                        02-Mar-20 19:46:59                                                                                                                                  
ponMyShell                     System.__ComObject                                                                                                                                  
ponProcess                     {System.Diagnostics.Process (aesm_service), System.Diagnostics.Process (ApplicationFrameHost), System.Diagnostics.Process (AppVShNotify)} 
#>


# Clear resource environment
Get-PSSession |
Remove-PSSession
<#
# Results

#>

[System.Runtime.InteropServices.Marshal]::
ReleaseComObject([System.__ComObject]$ponMyShell) |
Out-Null
<#
# Results

#>

[System.GC]::Collect()
[System.GC]::WaitForPendingFinalizers()
<#
# Results

#>

Get-Variable -Name 'pon*' |
ForEach { Get-Variable -Name $_ |
    Remove-Variable -Force }

# Validate clean-up
Get-Variable -Name 'pon*'

<#
# Results


#>

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