Why does a simple Powershell Interrupter with Start-Job, Wait-Job not return results? - powershell

Question

We have a jenkins git job that hangs on remote checking every so often. So I want to abort the checking with a timeout.
I understand that wait-job will return null if the timer had to stop the background job being awaited. So when a code block is long-running, it should return a null. That works for me in the command line.
However, when a job is short, the below code still getting null when I run the function in the ISE. When I debug it, it works fine. Help?
thank you!
Anne
function Test-TimeoutJob {
<#
.EXAMPLE
BUG:
> Test-TimeoutJob -theCodeBlock {write-output 'hi'}
Test-TimeoutJob : Type of theCodeBlock= scriptblock ; Text= write-output 'hi' .
Test-TimeoutJob : Return code from starting the job = , True .
Id Name PSJobTypeName State HasMoreData Location
-- ---- ------------- ----- ----------- --------
16 Job16 BackgroundJob Running True localhost
Test-TimeoutJob : Got null output of wait-job on id# 16 .
End : Now= 01/25/2016 17:12:02
#>
param (
$theCodeBlock , # infinite; $i=0; do {$i++; echo $i; } while ($true)
$theTimeoutSeconds = 1 # Beware; default=-1sec means wait infinitely #3
)
$thisFcn = 'Test-TimeoutJob'
# If null input, then set it.
if ( ! $theCodeBlock ) {
$theCodeBlock = {
#Show-TimeNow -theMessage "CodeBlock"
#Start-Sleep -Seconds 10
# your commands here, e.g.
Get-ChildItem *.cs | select name
}
}
$theCodeType = $theCodeBlock.GetType()
$theCodeStr = $theCodeBlock.ToString()
Write-Host "$thisFcn : Type of theCodeBlock= $theCodeType ; Text= $theCodeStr ."
$theJob = Start-Job -ScriptBlock $theCodeBlock
write-host "$thisFcn : Return code from starting the job = $LASTEXITCODE , $? ."
$jobid = $theJob.Id
Get-Job $jobid
$answaitobj = Wait-Job $theJob.Id -Timeout $theTimeoutSeconds
if ( $answaitobj -eq $null ) {
Write-Host "$thisFcn : Got null output of wait-job on id# $jobid . "
}
elseif ( $answaitobj ) {
$jobStatus = $theJob.State
$anstype = $answaitobj.GetType()
Write-Host "$thisFcn : the answer, supposed to be job, has type= $anstype ; status= $jobStatus ."
Stop-Job $theJob
$ansId = $theJob.Id
Write-Host "Job $ansId has been ended, with status= $jobStatus ; Thus it has finished or been stopped due to timeout."
# For our purposes of abending a script, we do not need to
# either get its data, which is null, or cleanup, which automatically occurs
# once jenkins finishes the call to posh.
# Get first element of output iterable
#$ans = Receive-Job -Job $theJob -Keep
#Remove-Job -force $theJob
}
Show-TimeNow -theMessage 'End'
}
function Show-TimeNow {
param (
$theMessage = 'Hello from Show-TimeNow'
)
$now = Get-Date
Write-Output "$theMessage : Now= $now"
}

Answer 1

The documentation never promises that Wait-Job would return anything if the timeout expires, so why would you expect it to?
-Timeout<Int32>
Determines the maximum wait time for each background job, in seconds. The default, -1, waits until the job completes, no matter how long it runs. The timing starts when you submit the Wait-Job command, not the Start-Job command.
If this time is exceeded, the wait ends and the command prompt returns, even if the job is still running. No error message is displayed.
Check the state of the job after Wait-Job returned to determine if the job is completed or not:
if ($job.State -eq 'Completed') {
Write-Host 'Finished.'
} else {
Write-Host 'Timeout expired. Stopping job.'
Stop-Job -Id $job.Id
}

Answer 2

The answer turned out that, on my system, one second was too short of a timeout, even for the simplest program. Setting the timeout to a longer number of seconds returned the expected results.