Powershell Asynchronous Function Call - powershell

Question

I'm trying to create some sort of Service Script that notifies me when a specific computer in the network is online. To achieve this, I'd like to have a function that runs in the background and checks every x seconds whether the computer is reachable (through an ICMP package) or not.
Pseudo code:
class Computer{
[bool]$IsOnline
[ScriptBlock]$InvokeFunction = {
Notify()
}
}
$collectionOfComputers = #()
function Invoke-Worker{
while($true){
foreach($computer in $collectionOfComputers){
ping $computer
if($computer.IsOnline){
$computer.InvokeFunction()
}
}
Start-Sleep -Seconds 10
}
}
I hope what I'm trying to do is achievable with powershell and the question is okay to be asked.

Answer 1

Basic structure but I think meets all of the requirements you mentioned and some you don't:
$Status = #{}
while ($true)
{
## By continually retrieving the contents of the file, will allow you to update the input on the fly and have the script dynamically adjust
$Computers = Get-Content 'computers.txt'
if ($Computers.Count -gt 0)
{
foreach ($Computer in $Computers)
{
if (-not($Status[$Computer]))
{
$Status[$Computer] = [pscustomobject]#{
Name = $Computer
IsOnline = $false
StateChange = $null
}
}
## If IsOnline NOW
if (Test-Connection $Computer -Count 1 -Quiet)
{
## If IsOnline NOW compared to the state on the last poll
if ($Status[$Computer].IsOnline)
{
$Status[$Computer].StateChange = $false
}
else
{
$Status[$Computer].StateChange = $true
}
## Set the new online state for our object
$Status[$Computer].IsOnline = $true
}
else
{
## If IsOnline NOW compared to the state on the last poll
if ($Status[$Computer].IsOnline)
{
$Status[$Computer].StateChange = $true
}
else
{
$Status[$Computer].StateChange = $false
}
## Set the new online state for our object
$Status[$Computer].IsOnline = $false
}
}
}
$Status
Start-Sleep -Seconds 10
}
Variant: Producer/Consumer Parallelism -- without the Producer (still have to poll the output object to retrieve the results, even though the icmp polling is happening in a different runspace)
## Adapted from Lee Holmes Producer/Consumer Parallelism here: https://www.leeholmes.com/blog/2018/09/05/producer-consumer-parallelism-in-powershell/
$parallelScript = {
param(
## The output buffer to write responses to
$OutputQueue,
## State tracking, to help threads communicate
## how much progress they've made
$ThreadId, $ShouldExit
)
## Continually work until
## the 'ShouldExit' flag is set
$Status = #{}
$workItem = $null
while(! $ShouldExit.Value)
{
## By continually retrieving the contents of the file, will allow you to update the input on the fly and have the script dynamically adjust
$Computers = Get-Content 'C:\users\user\Desktop\computers.txt'
if ($Computers.Count -gt 0)
{
foreach ($Computer in $Computers)
{
if (-not($Status[$Computer]))
{
$Status[$Computer] = [pscustomobject]#{
Name = $Computer
IsOnline = $false
StateChange = $null
}
}
## If IsOnline NOW
if (Test-Connection $Computer -Count 1 -Quiet)
{
## If IsOnline NOW compared to the state on the last poll
if ($Status[$Computer].IsOnline)
{
$Status[$Computer].StateChange = $false
}
else
{
$Status[$Computer].StateChange = $true
}
## Set the new online state for our object
$Status[$Computer].IsOnline = $true
}
else
{
## If IsOnline NOW compared to the state on the last poll
if ($Status[$Computer].IsOnline)
{
$Status[$Computer].StateChange = $true
}
else
{
$Status[$Computer].StateChange = $false
}
## Set the new online state for our object
$Status[$Computer].IsOnline = $false
}
}
}
Start-Sleep -Seconds 10
## Add the result to the output queue
$OutputQueue.Enqueue($Status)
}
else
{
## If there was no work, wait a bit for more.
Start-Sleep -m 100
}
}
## Create a set of background PowerShell instances to do work, based on the
## number of available processors.
$threads = 1
$runspaces = 1..$threads | Foreach-Object { [PowerShell]::Create() }
$outputProgress = New-Object 'Int[]' $threads
$outputQueue = New-Object 'System.Collections.Concurrent.ConcurrentQueue[Object]'
$shouldExit = $false
## Spin up each of our PowerShell runspaces. Once invoked, these are actively
## waiting for work and consuming once available.
for($counter = 0; $counter -lt $threads; $counter++)
{
$null = $runspaces[$counter].AddScript($parallelScript).
AddParameter("OutputQueue", $outputQueue).
AddParameter("ThreadId", $counter).
AddParameter("ShouldExit", [ref] $shouldExit).BeginInvoke()
}
## Wait for our worker threads to complete processing the
## work.
try
{
do
{
## If there were any results, output them.
$scriptOutput = $null
while($outputQueue.TryDequeue([ref] $scriptOutput))
{
$scriptOutput
}
Start-Sleep -m 100
## See if we still have any busy runspaces. If not, exit the loop.
$busyRunspaces = $runspaces | Where-Object { $_.InvocationStateInfo.State -ne 'Complete' }
} while($busyRunspaces)
}
finally
{
## Clean up our PowerShell instances
foreach($runspace in $runspaces)
{
$runspace.Stop()
$runspace.Dispose()
}
}

Answer 2

You need to pass the collection of computers to invoke-worker. When you pass the variable to a function you will get a copy of $collectionOfComputers then you can use start-job.
function Invoke-Worker($collectionOfComputers){
while($true){
foreach($computer in $collectionOfComputers){
ping $computer
if($computer.IsOnline){
$computer.InvokeFunction()
}
}
Start-Sleep -Seconds 10
}
}
The class Computer must be part of the job.