PR Summary

There is a race condition where PipelineProcess.Stop() can be called after Dispose() has already disposed the token. This causes the Stop() call to raise ObjectDisposedException crashing the process. An explicitly registered action on
$PSCmdlet.PipelineStopToken.Register() can also throw an exception which is not handled in the stop call causing a similar crash.

The fix is to ignore AggregateException which contains any exceptions raised by the user defined delegates on the stop token and exit early if the token has been disposed. We exit early because Dispose() has already done the work and there is nothing left to stop.

PR Context

Fixes: #28299

It also fixes a related problem where if the delegate registered by a caller could throw which is raised as an AggregateException. In C# this wouldn't typically happen but if someone in PowerShell provided any ScriptBlock delegate the cancellation will most likely be triggered somewhere that doesn't have a runspace. For example:

function Test-Stop {
    [CmdletBinding()] param()
    $null = $PSCmdlet.PipelineStopToken.Register([Action]{ })
    Start-Sleep 30
}

Test-Stop  # press Ctrl+C

The fix is to ignore AggregateException so that this exception, any anything else a registered delegate a C# cmdlet would register, do not bring down the process.

This should be considered for backporting as well. While it is a race condition, the issue from #28299 shows that it can crash the whole process.

PR Checklist

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• Breaking changes
  • None
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  • Not Applicable
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  • Documentation needed
    • Issue filed:
• Testing - New and feature
  • N/A or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed