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You know that most of the administrative tasks you perform on a SharePoint Farm can be accomplished using PowerShell scripting. You get a bunch of commandlets (more than 600 indeed!) that are registered through the Microsoft.SharePoint.PowerShell snapin, and you can even add your own commandlets using standard SharePoint deployment techiques.

That’s why sometime you just end up firing the default PowerShell console and typing

Add-PSSnapIn Microsoft.SharePoint.PowerShell

Well… you get something that is “similar” to the SharePoint Management Shell

The SharePoint Management Shell is nothing more than a standard PowerShell console (powershell.exe) where tha snapin is automatically loaded upon startup, leveraging a startup script:

C:\Windows\System32\WindowsPowerShell\v1.0\PowerShell.exe  -NoExit  ” & ‘ C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\CONFIG\POWERSHELL\Registration\\sharepoint.ps1 ‘ “

The sharepoint.ps1 script is just a few lines of code:

$ver = $host | select version
if ($ver.Version.Major -gt 1)  {$Host.Runspace.ThreadOptions = “ReuseThread”}
Add-PsSnapin Microsoft.SharePoint.PowerShell
Set-location $home

In the above snippet you can notice the automatic loading of the SharePoint snapin and a “change directory” instruction that brings you to your default home directory (tipically, c:\users\yourusername).

But there’s an additional line:

if ($ver.Version.Major -gt 1) {$Host.Runspace.ThreadOptions = “ReuseThread”}

This line sets the PSThreadOptions of the PowerShell runspace to ReuseThread, which means that the same thread is used for all command line invocations since the shell has started.

The other options are (see http://msdn.microsoft.com/it-it/library/system.management.automation.runspaces.psthreadoptions(v=vs.85).aspx):

• Default
  On the local computer, UseNewThread is used for runspaces and ReuseThread is used for runspace pools. Server settings are used for remote runspaces and runspace pools. This field is introduced in Windows PowerShell 2.0.
• ReuseThread
  Creates a new thread for the first invocation and then re-uses that thread in subsequent invocations. This field is introduced in Windows PowerShell 2.0.
• UseCurrentThread
  Execution occurs on the thread that called the Invoke method. This option is not valid for asynchronous calls. This field is introduced in Windows PowerShell 2.0.
• UseNewThread
  Creates a new thread for each invocation. This field is introduced in Windows PowerShell 2.0.

If you want a proof of this behavior, just run both a standard powershell console and a SharePoint Management Shell, then run the followind command a few times in each shell.

[Threading.Thread]::CurrentThread.ManagedThreadId

This instruction prints the internal identifier of the managed thread (i.e. the CLR Thread object)

You’ll notice that you get the same value in the SharePoint Management Shell, whereas you get different values in the standard one. By the way, PowerShell ISE uses the ReuseThread option too.

What’s the issue with the default value, i.e. having a new thread spawn (or picked up from a pool) for every command invocation?

Well… first of all there are some SharePoint objects that are not completely thread safe, sou you should pay careful attention when using them from different threads (even if, in this particular case, you have multiple threads that are not executed in parallel )

Another noticeable issue you may experience, though, is resource leakage: if you create SharePoint objects in one thread and suddenly have no reference to that thread any longer, you end up wasting resources that are not disposed correctly.

Wrapping it up… the SharePoint Management Shell is nothing special, but it’s a little bit more than adding a snap in!!