RPC_E_SERVERCALL_RETRYLATER during powershell automation

Question

RPC_E_SERVERCALL_RETRYLATER during powershell automation

I'm using PowersHell to automate iTunes but find the error handling / waiting for com objects handling to be less than optimal.

Example code

#Cause an RPC error
$iTunes = New-Object -ComObject iTunes.Application
$LibrarySource = $iTunes.LibrarySource
# Get "playlist" objects for main sections
foreach ($PList in $LibrarySource.Playlists)
{
  if($Plist.name -eq "Library") {
    $Library = $Plist
  }
}
do {
  write-host -ForegroundColor Green "Running a loop"
  foreach ($Track in $Library.Tracks)
  {
     foreach ($FoundTrack in $Library.search("$Track.name", 5)) {
       # do nothing... we don't care...
       write-host "." -nonewline
     }
  }
} while(1) 
#END

Go into itunes and do something that makes it pop up a message - in my case I go into the Party Shuffle and I get a banner "Party shuffle automatically blah blah...." with a "Do not display" message.

At this point if running the script will do this repeatedly:

+      foreach ($FoundTrack in $Library.search( <<<< "$Track.name", 5)) {
Exception calling "Search" with "2" argument(s): "The message filter indicated
that the application is busy. (Exception from HRESULT: 0x8001010A (RPC_E_SERVER
CALL_RETRYLATER))"
At C:\Documents and Settings\Me\My Documents\example.ps1:17 char:45
+      foreach ($FoundTrack in $Library.search( <<<< "$Track.name", 5)) {
Exception calling "Search" with "2" argument(s): "The message filter indicated
that the application is busy. (Exception from HRESULT: 0x8001010A (RPC_E_SERVER
CALL_RETRYLATER))"
At C:\Documents and Settings\Me\My Documents\example.ps1:17 char:45

If you waited until you you had a dialog box before running the example then instead you'll get this repeatedly:

Running a loop
You cannot call a method on a null-valued expression.
At C:\Documents and Settings\Me\example.ps1:17 char:45
+      foreach ($FoundTrack in $Library.search( <<<< "$Track.name", 5)) {

That'll be because the $Library handle is invalid.

If my example was doing something important - like converting tracks and then deleting the old ones, not handling the error correctly could be fatal to tracks in itunes. I want to harden up the code so that it handles iTunes being busy and will silently retry until it has success. Any suggestions?

powershell

itunes

asked on Stack Overflow Oct 8, 2008 by

Paul Hargreaves

3 Answers

COM support in PowerShell is not 100% reliable. But I think the real issue is iTunes itself. The application and COM model wasn't designed, IMO, for this type of management. That said, you could implement a Trap into your script. If an exception is raised, you could have the script sleep for a few seconds.

answered on Stack Overflow Oct 8, 2008 by

Jeffery Hicks

Here's a function to retry operations, pausing in between failures:

function retry( [scriptblock]$action, [int]$wait=2, [int]$maxRetries=100 ) {
  $results = $null

  $currentRetry = 0
  $success = $false
  while( -not $success ) {
    trap {
      # Set status variables at function scope.
      Set-Variable -scope 1 success $false
      Set-Variable -scope 1 currentRetry ($currentRetry + 1)

      if( $currentRetry -gt $maxRetries ) { break }

      if( $wait ) { Start-Sleep $wait }
      continue
    }

    $success = $true
    $results = . $action
  }

  return $results
}

For the first error in your example, you could change the inner foreach loop like this:

$FoundTracks = retry { $Library.search( "$Track.name", 5 ) }
foreach ($FoundTrack in $FoundTracks) { ... }

This uses the default values for $wait and $maxRetries, so it will attempt to call $Library.search 100 times, waiting 2 seconds between each try. If all retries fail, the last error will propagate to the outer scope. You can set $ErrorActionPreference to Stop to prevent the script from executing any further statements.

answered on Stack Overflow Oct 19, 2008 by

Emperor XLII

Part of your problem might be in how $Track.name is being evaluated. You could try forcing it to fully evaluate the name by using $($Track.name).

One other thing you might try is using the -strict parameter with your new-object command/

answered on Stack Overflow Oct 9, 2008 by

Steven Murawski

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