Powershell starting a process within a loop

Question

I am trying to write a load balanced powershell publishing script and have seem to hit a roadblock. The foreach loop below will spin up a process to deploy using MSDeploy given the arguments.

foreach ($server in $ServersToDeploy) {
    # Spin up a new process
    $pinfo = New-Object System.Diagnostics.ProcessStartInfo
    $pinfo.FileName = $MSDeploy
    $pinfo.RedirectStandardError = $true
    $pinfo.RedirectStandardOutput = $true
    $pinfo.UseShellExecute = $false
    $pinfo.Arguments = $arguments
    $p = New-Object System.Diagnostics.Process
    $p.StartInfo = $pinfo
    $p.Start() | Out-Null
    $p.WaitForExit()
    $stdout = $p.StandardOutput.ReadToEnd()
    $stderr = $p.StandardError.ReadToEnd()

    # Output
    if ($stderr) {
        throw $stderr + ("Exit Code: " + $p.ExitCode)
    }
    Write-Host $stdout
}

On the first run, it will run the script and execute MSDeploy with the proper arguments, but powershell would indefinitely wait for the first process to exit, but the publish seems to have executed successfully for both servers because when I re-run the command, the process executes quickly and properly for both servers with no changes.

This makes me think that this might be a timing issue, because when the publish goes through fast, it seems to work but when it's slow, it hangs on the first iteration of the publish.

You have possible deadlock here: $p.WaitForExit(); $stdout = $p.StandardOutput.ReadToEnd(); $stderr = $p.StandardError.ReadToEnd(). — user4003407
– user4003407, Commented Apr 25, 2016 at 22:25

chief7 · Accepted Answer · 2016-04-26 10:15:19Z

2

Move the ReadToEnd calls above the WaitForExit

...
$p.Start() | Out-Null
$stdout = $p.StandardOutput.ReadToEnd()
$stderr = $p.StandardError.ReadToEnd()
$p.WaitForExit()
...

answered Apr 26, 2016 at 10:15

chief7

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1 Comment

user4003407 Over a year ago

You still have possibility for deadlock. You can stuck at reading StandardOutput but process can stuck at writing in StandardError.

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