InvocationStateChanged Event Raised Twice in PowerShell Script - powershell

Question

I have been writing a script in PowerShell V4 on Windows 8.1 which makes use of background processes and events. I have found something which is a little strange. Rather than post the 2,500 lines or so of my script I have included a much shorter program which exhibits the odd behaviour. I expect it is something I am doing wrong but I cannot see what the problem is. The code is as follows:
`
# Scriptblocks to simulate the background task and the action to
# take when an event is raised
[scriptblock] $MyScript = {
for ($i = 0;$i -lt 30;$i++)
{
[console]::writeline("This is a test - $i")
start-sleep -m 500
}
}
[scriptblock] $StateChanged = {
[console]::writeline("The state changed")
}
# Create a runspace pool
$RunspacePool = [RunspaceFactory]::CreateRunspacePool(1, [int] $env:NUMBER_OF_PROCESSORS + 1)
$RunspacePool.ApartmentState = "MTA"
$RunspacePool.Open()
# Create and start the background task to run
$PS = [powershell]::Create()
[void] $PS.AddScript($MyScript)
$PS.RunspacePool = $RunspacePool
$Asyncresult = $PS.BeginInvoke()
# Register an interest in the InvocationStateChanged event for
# the background task. Should the event happen (which it will)
# run the $StateChanged scriptblock
Register-ObjectEvent -InputObject $PS -EventName InvocationStateChanged -Action $StateChanged
# The loop that simulates the main purpose of the script
[int] $j = 0
while ($PS.InvocationStateInfo.State -eq [System.Management.Automation.PSInvocationState]::Running)
{
if ($j -eq 2)
{
[void] $PS.BeginStop($NULL, $NULL)
}
"Running: $j" | out-host
sleep -m 400
$j = $j + 1
}
sleep 10
`
Essentially all it does is create a runspace to run a powershell scriptblock and while that is running something else happens in the foreground. I simulate someone pressing a button or, for whatever reason, a beginstop method being executed to stop the background process. That all works and the background process duly stops. However, I have registered an event for the background powershell script which runs a scriptblock when the background job changes state. The strange thing is that the scriptblock gets invoked twice and I cannot work out why.
Here is some output from running the script:
E:\Test Programs>powershell -file .\strange.ps1
This is a test - 0
Running: 0
This is a test - 1
Running: 1
The state changed
Running: 2
The state changed
E:\Test Programs>
As you can see it displays "The state changed" twice. They are a fraction of a second apart. I put a sleep 10 at the end to eliminate the possibility that it is the script stopping that is causing the second "The state changed" message.
If anyone can explain what is wrong I would be very grateful.

Answer 1

The InvocationStateChanged event is likely being called when on Running and Completed
If you change $StateChanged to also include the $Sender.InvocationStateInfo.State automatic variable properties, like this:
[scriptblock] $StateChanged = {
[console]::writeline("The state changed to: $($Sender.InvocationStateInfo.State)")
}
Your output will probably look like:
This is a test - 0
Running: 0
This is a test - 1
Running: 1
The state changed to: Running
Running: 2
The state changed: Completed

Answer 2

I am very sorry that I didn't reply a year and a half ago as I should have done. For some reason I never had a notification that there was an answer and, to be honest, I just forgot to check.
Anyway, thanks for the answer. I still have my little test script although the thing I was actually writing has been dumped and rewritten but I did check with my little test script and what I get is:
Running: 0
Running: 1
This is a test - 1
The state changed to: Stopped
The state changed to: Stopped
Running: 2
This is now on Windows 10.
Oh well, thanks for the suggestion anyway. As I said I've rewritten the original script so this is now just for interest.
Best wishes........
Colin