Start-Job passing XML object to -ArgumentList work

Question

I'm testing a deployment script for my application on Windows Server 2012 with Powershell v3. The script runs fine on Win Server 2008 R2 and Win 7 with Powershell v2. The issue I'm running into now is that I can not access properties of XML variables passed via -ArgumentList.

I've been able to reproduce the issue on Win 7 and Win Server 2012 with Powershell v3 in a simple script that doesn't have any of the SharePoint, IIS, misc that my main script does.

Script (I think I borrowed this from a similar question I can't find now):

$xml = [xml] (Get-Content (Get-Item (".\input.xml")))
$foobar = $xml.Stuff.FooBars.Foobar 

$ScriptBlock = {        
    $foobar = $args[0]

    write-host "Inside the job..."
    write-host ("Foobar     : "+$foobar)
    write-host ("Foobar.Foo : "+$foobar.Foo)
}

write-host "Outside the job..."
write-host ("Foobar: "+$foobar)
write-host ("Foobar.Foo : "+$foobar.Foo)

Start-Job -ScriptBlock $ScriptBlock -ArgumentList $foobar | Out-Null        
While (Get-Job -State "Running") { Start-Sleep 2 }               

write-host ("Jobs Completed.")    
Get-Job | Receive-Job          
Remove-Job * 

The Input XML:

<?xml version="1.0"?>
<Stuff xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <FooBars>
    <FooBar>
      <Foo>ThisIsAFoo</Foo>
     <Bar>ThisIsABar</Bar>
    </FooBar>
  </FooBars> 
</Stuff>

Output from Powershell v2:

PS C:\Powershell3Issues> .\demo.ps1
Outside the job...
Foobar: System.Xml.XmlElement
Foobar.Foo : ThisIsAFoo
Jobs Completed.
Inside the job...
Foobar     : System.Collections.ArrayList System.Collections.ArrayList
Foobar.Foo : ThisIsAFoo

Output from Powershell v3:

PS C:\Powershell3Issues> .\demo.ps1
Outside the job...
Foobar: System.Xml.XmlElement
Foobar.Foo : ThisIsAFoo
Jobs Completed.
Inside the job...
Foobar     : System.Collections.ArrayList System.Collections.ArrayList
Foobar.Foo :

Note the missing Foobar.Foo value.

I've also tried the $using syntax in v3 but it does the same thing.

Answer 1

I'm using PS 3.0 and it does change data types. I modified your script to take a look:

$xml = [xml] (Get-Content .\input.xml)
$foobar = $xml.Stuff.FooBars.Foobar 
"Foobar Outside type = $($foobar.Gettype())"

$ScriptBlock = {        
    $foobar = $args[0]
    "Foobar Inside type = $($foobar.Gettype())"
}

Start-Job -ScriptBlock $ScriptBlock -ArgumentList $foobar | Out-Null
While (Get-Job -State "Running") { Start-Sleep 2 }     
Get-Job | Receive-Job 

The output I got was:

Foobar Outside type = System.Xml.XmlElement
Foobar Inside type = System.Collections.ArrayList System.Collections.ArrayList

I'll keep looking and see what I find.

Update:

When I run the script in PS 2.0 using the command powershell -version 2.0 I get an error saying:

Method invocation failed because [Deserialized.System.Xml.XmlElement] doesn't contain a method named 'Gettype'.
+ CategoryInfo          : InvalidOperation: (Gettype:String) [], RuntimeException
+ FullyQualifiedErrorId : MethodNotFound
+ PSComputerName        : localhost 

It changes from System.Xml.XmlElement to Deserialized.System.Xml.XmlElement, right? I'll keep looking and see what I find.

Workaround:

A workaround could be instead of passing an object just pass a string.

$xml_path = 'C:\input.xml'
$sb = {
    $xml = [xml](Get-Content $args[0])
    ...
}
Start-Job -ScriptBlock $sb -Args $xml_path

I'm done searching. My head hurts when I go in depth on things.

Answer 2

The problem is you are trying to serialise an object of type XMLElement which does not serialise. The workaround is to clone the XMLElement and wrap it in a new XMLDocument.

cls

$XMLDocument = [xml]@"
<?xml version="1.0"?>
<Stuff xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <FooBars>
    <FooBar>
      <Foo>ThisIsAFoo1</Foo>
      <Bar>ThisIsABar2</Bar>
    </FooBar>
    <FooBar>
      <Foo>ThisIsAFoo2</Foo>
      <Bar>ThisIsABar2</Bar>
    </FooBar>
  </FooBars> 
</Stuff>
"@

Select-Xml -Xml $XMLDocument -XPath 'Stuff/FooBars/FooBar' | foreach {  
  $SelectedNode = $_.Node
  #$SelectedNode is now of type System.Xml.XmlElement which does not serialise
  #but System.Xml.XmlDocument will serialise so wrap a clone of $SelectedNode in a new XMLDocument 
  #then pass that as the argument
  $SerializationWrapper = New-Object System.Xml.XmlDocument  
  $SerializationWrapper.AppendChild($SerializationWrapper.ImportNode($SelectedNode, $true)) | Out-Null
  Start-Job -ScriptBlock {
    param($xml)
    Write-Output "Start Job"    
    'The type of deserialise object $xml is: ' + $xml.getType()    
    $sw = New-Object system.io.stringwriter 
    $writer = New-Object system.xml.xmltextwriter($sw) 
    $writer.Formatting = [System.xml.formatting]::Indented 
    $xml.WriteContentTo($writer) 
    $sw.ToString()  
    Write-Output "Finish Job"    
    Write-Output ""    
  } -ArgumentList $SerializationWrapper
}

Get-Job | Wait-Job | Receive-Job

As you can see from the following output 2 jobs were spawned and a single wrapped FooBar element is passed for formatting.

Id     Name            PSJobTypeName   State         HasMoreData     Location             Command                  
--     ----            -------------   -----         -----------     --------             -------                  
520    Job520          BackgroundJob   Running       True            localhost            ...                      
522    Job522          BackgroundJob   Running       True            localhost            ...                      
Start Job
The type of deserialise object $xml is: xml
<FooBar>
  <Foo>ThisIsAFoo1</Foo>
  <Bar>ThisIsABar2</Bar>
</FooBar>
Finish Job

Start Job
The type of deserialise object $xml is: xml
<FooBar>
  <Foo>ThisIsAFoo2</Foo>
  <Bar>ThisIsABar2</Bar>
</FooBar>
Finish Job

Answer 3

Try this to specify the version of PowerShell to run the job under:

Start-Job -ScriptBlock $ScriptBlock -ArgumentList $foobar -PSVersion 2.0