PowerShell Jobs vs Start-Process - powershell

Question

I made a little diagnostic script that I keep in my $profile. In collecting the CPU name I found that the command takes about 4 seconds (Get-WmiObject -Class Win32_Processor).Name. So I thought I'd try PowerShell Jobs and while I think they will be really good for long background jobs, if you just want to quickly grab a small piece of information in the background, the initialisation times are awkward (like 2-3 sec per job) so I thought I'd use Start-Process to dump values in temp files while the rest of my script runs. I think I'm doing this correctly, but if you run this function 3 or 4 times, you'll notice that CPU name is not populated.
• Is using Start-Process like this optimal, or does anyone have a quicker way to just start small jobs in the background in parallel? I know there is a .NET way of doing this (but it seems super-complex from what I've seen)?
• Do you know why my "wait for file to be created and be non-zero before accessing it" is failing so regularly?
function sys {
$System = get-wmiobject -class "Win32_ComputerSystem"
$Mem = [math]::Ceiling($System.TotalPhysicalMemory / 1024 / 1024 / 1024)
$wmi = gwmi -class Win32_OperatingSystem -computer "."
$LBTime = $wmi.ConvertToDateTime($wmi.Lastbootuptime)
[TimeSpan]$uptime = New-TimeSpan $LBTime $(get-date)
$s = "" ; if ($uptime.Days -ne 1) {$s = "s"}
$uptime_string = "$($uptime.days) day$s $($uptime.hours) hr $($uptime.minutes) min $($uptime.seconds) sec"
$temp_cpu = "$($env:TEMP)\ps_temp_cpu.txt"
$temp_cpu_cores = "$($env:TEMP)\ps_temp_cpu_cores.txt"
$temp_cpu_logical = "$($env:TEMP)\ps_temp_cpu_logical.txt"
rm -force $temp_cpu -EA silent ; rm -force $temp_cpu_cores -EA silent ; rm -force $temp_cpu_logical -EA silent
Start-Process -NoNewWindow -FilePath "powershell.exe" -ArgumentList "-NoLogo -NoProfile (Get-WmiObject -Class Win32_Processor).Name > $temp_cpu"
Start-Process -NoNewWindow -FilePath "powershell.exe" -ArgumentList "-NoLogo -NoProfile (Get-WmiObject -Class Win32_Processor).NumberOfCores > $temp_cpu_cores"
Start-Process -NoNewWindow -FilePath "powershell.exe" -ArgumentList "-NoLogo -NoProfile (Get-WmiObject -Class Win32_Processor).NumberOfLogicalProcessors > $temp_cpu_logical"
""
"Hostname: $($System.Name)"
"Domain: $($System.Domain)"
"PrimaryOwner: $($System.PrimaryOwnerName)"
"Make/Model: $($System.Manufacturer) ($($System.Model))" # "ComputerModel: $((Get-WmiObject -Class:Win32_ComputerSystem).Model)"
"SerialNumber: $((Get-WmiObject -Class:Win32_BIOS).SerialNumber)"
"PowerShell: $($PSVersionTable.PSVersion)"
"Windows Version: $($PSVersionTable.BuildVersion)"
"Windows ReleaseId: $((Get-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion' -Name 'ReleaseId').ReleaseId)"
"Display Card: $((Get-WmiObject -Class:Win32_VideoController).Name)"
"Display Driver: $((Get-WmiObject -Class:Win32_VideoController).DriverVersion)"
"Display ModelDesc: $((Get-WmiObject -Class:Win32_VideoController).VideoModeDescription)"
"Last Boot Time: $([Management.ManagementDateTimeConverter]::ToDateTime((Get-WmiObject Win32_OperatingSystem | select 'LastBootUpTime').LastBootUpTime))" # $(wmic OS get LastBootupTime)
"Uptime: $uptime_string"
# ipconfig | sls IPv4
Get-Netipaddress | where AddressFamily -eq IPv4 | select IPAddress,InterfaceIndex,InterfaceAlias | sort InterfaceIndex
# Get-PSDrive | sort -Descending Free | Format-Table
# https://stackoverflow.com/questions/37154375/display-disk-size-and-freespace-in-gb
# https://www.petri.com/checking-system-drive-free-space-with-wmi-and-powershell
# https://www.oxfordsbsguy.com/2017/02/08/powershell-how-to-check-for-drives-with-less-than-10gb-of-free-diskspace/
# Get-Volume | Where-Object {($_.SizeRemaining -lt 10000000000) -and ($_.DriveType -eq “FIXED”) -and ($_.FileSystemLabel -ne “System Reserved”)}
gwmi win32_logicaldisk | Format-Table DeviceId, VolumeName, #{n="Size(GB)";e={[math]::Round($_.Size/1GB,2)}},#{n="Free(GB)";e={[math]::Round($_.FreeSpace/1GB,2)}}
# Note: -EA silent on Get-Item otherwise get an error
while (!(Test-Path $temp_cpu)) { while ((Get-Item $temp_cpu -EA silent).length -eq 0kb) { Start-Sleep -Milliseconds 500 } }
"CPU: $(cat $temp_cpu)"
while (!(Test-Path $temp_cpu_cores)) { while ((Get-Item $temp_cpu_cores -EA silent).length -eq 0kb) { Start-Sleep -Milliseconds 500 } }
"CPU Cores: $(cat $temp_cpu_cores)"
while (!(Test-Path $temp_cpu_logical)) { while ((Get-Item $temp_cpu_logical -EA silent).length -eq 0kb) { Start-Sleep -Milliseconds 500 } }
"CPU Logical: $(cat $temp_cpu_logical)"
rm -force $temp_cpu -EA silent ; rm -force $temp_cpu_cores -EA silent ; rm -force $temp_cpu_logical -EA silent
"Memory: $(Get-CimInstance Win32_PhysicalMemory | Measure-Object -Property capacity -Sum | Foreach {"{0:N2}" -f ([math]::round(($_.Sum / 1GB),2))}) GB"
""
"Also note the 'Get-ComputerInfo' Cmdlet (has more info but slower to run)"
""
}

Answer 1

To run jobs in background in powershell, there are these 3 ways to go about it
1. Invoke-Command[3] -scriptblock { script } -asJob -computername localhost
2. Start-Job[2] -scriptblock { script }
3. Start-Process[1] powershell {script}
If you truly want to run things in the background with each job being independent of each other, you'll have to think about using the first or second option as neither of them require the output to be written to a file.
Invoke-Command starts a new session with the system and runs the job in a new instance.
Start-Job creates a new job in the background under a new powershell instance, takes a little more time to allocate the resources and start the process. Just like start-process, Start-Job will run the job in a separate powershell.exe instance.
Start-Process requires you to redirect the standard output to a file[1]. You have to rely on the performance of the disk and how fast your reads and writes are. You also have to ensure that no more than one thread is reading/writing to the output of this process.
Recommendation
I found Invoke-Command to be the fastest when running 100 concurrent jobs to get the processor info. This option does require you to provide -ComputerName which then requires you to be an admin to start a winrm Session with localhost. If you dont output the job information while creating the jobs, it does not take away any significant time.
Start-Job and Invoke-Command both took about a second to get the processor info and running 100 concurrent jobs to get the same thing took some overhead.
$x = 0..100 | Invoke-Command -computername localhost -scriptblock { script } -asJob
$x | % { $_ | wait-job | out-null }
$output = $x | % { $_ | Receive-Job}
# You can run measure-object, sort-object, etc as well
[1]Start-Process
RedirectStandardOutput: Specifies a file. This cmdlet sends the output generated by the process to a file that you specify. Enter the path and filename. By default, the output is displayed in the console.
[2]Start-Job
The Start-Job cmdlet starts a PowerShell background job on the local computer. ... A PowerShell background job runs a command without interacting with the current session.
[3]Invoke-Command
The Invoke-Command cmdlet runs commands on a local or remote computer and returns all output from the commands, including errors. ... To run a command in a background job, use the AsJob parameter