I'm confused how -Passthru works.
From my understanding, the -Passthru parameter is used for passing the result of a cmdlet to the pipeline even the cmdlet itself doesn't produce any results.
I tried to write these code first: (I'm trying to recycle the IIS Application Pool without using Restart-WebAppPool cmdlet)
Stop-WebAppPool -Name Foo
Start-WebAppPool -Name Foo
As I expected, it takes time to stop a IIS ApplicationPool, and since PowerShell does not wait for cmdlets to finish their job, the Stop-WebAppPool stops the application pool and returns. Because the application pool is not ready to get started, the Start-WebAppPool is called and error is thrown.
So I changed my code into these:
Stop-WebAppPool -Name Foo
Start-Sleep -Seconds SomeValueNeedToGetMeasuredAndChanged
Start-WebAppPool -Name Foo
It works but not very elegent and flexible.
Then I add -Passthru to both of the cmdlets, it becomes:
Stop-WebAppPool -Name Foo -Passthru
Start-WebAppPool -Name Foo -Passthru
Everything goes fine and no error is thrown.
In my case, I suppose:
The Stop/Start-WebAppPool cmdlet does not produce any results until the Application Pool really get stopped/started. Since -Passthru requires something to pass to the pipeline, PowerShell waits for the cmdlet produces its result, in this case, application pool get stopped/started, to execute the next one.
I can't find any useful manuals on either -Passthru or Stop-WebAppPool, so is it alright to do so in this case?
-Passthru is used to pass current object (i.e. AppPool) further down the pipeline. I don't think that it's guaranteed, that Start/Stop-WebAppPool cmdlets will wait for current operation to complete before passing down AppPool object. It works now, but it could break later.
Solution? Use Restart-WebAppPool. Or if you really need to use Start/Stop cmdlets, do it like this:
$AppPool = 'Foo'
Stop-WebAppPool -Name $AppPool
while((Get-WebAppPoolState -Name $AppPool).Value -ne 'Stopped'){
Start-Sleep 1
}
Start-WebAppPool -Name $AppPool