Start-Sleep memory leak (or causing powershell memory leak)? - powershell

Question

This question is a repost from https://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/365ca396-400d-4401-bd7f-05d5d6c22cc8/powershells-startsleep-causes-memory-growth?forum=winserverpowershell
I did not get a working answer there so try if this forum can help. This is blocking my work.
Here is my two powershell scripts. The first one is to create an event source and the second one is to generate events using 4 threads. Start-Sleep is used in each thread to control the event generation rate. If I remove the Start-Sleep, then the powershell memory usage is constant, otherwise it grows fast until all system memory is used and the system becomes extremely slow.
Is this a known issue? Any workaround? Appreciate any clue.
# use this script to create channel and source if they does not exist.
$logName = "TestLog"
$sourceName = "TestSource"
New-EventLog -LogName $logName -Source $sourceName
# maximumSize's max is 4G.
Limit-EventLog -LogName $logName -OverflowAction OverWriteOlder -RetentionDays 30 -MaximumSize 3080000KB
Event generating script:
# use this script to generate events in TestLog channel.
Param(
[int]$sleepIntervalInMilliSeconds = 0
)
$eventGenScript = {
$logName = "TestLog"
$sourceName = "TestSource"
while($true) {
Write-EventLog -LogName $logName -Source $sourceName -Message "perfLog" -EventId 0 -EntryType information
Start-Sleep -ms $sleepIntervalInMilliSeconds
}
}
$threadCount = 4
for($i=0; $i -lt $threadCount; $i++)
{
Start-Job $eventGenScript
}
read-host "type a key to exit. You need to wait for some time for threads to exit."

Answer 1

It's not that Start-Sleep has a memory leak, you're calling it with an invalid Parameter (-ms) and the process memory of the jobs is filling up with error messages, because you keep calling the (invalid) statement in an infinite loop.
Demonstration:
PS C:\> Start-Sleep -ms 100
Start-Sleep : A parameter cannot be found that matches parameter name 'ms'.
At line:1 char:13
+ Start-Sleep -ms 100
+ ~~~
+ CategoryInfo : InvalidArgument: (:) [Start-Sleep], ParameterBindingException
+ FullyQualifiedErrorId : NamedParameterNotFound,Microsoft.PowerShell.Commands.StartSleepCommand
Also, you're defining $sleepIntervalInMilliSeconds outside the scriptblock, but try to use it inside the scriptblock, which won't work, because the variable is undefined in the scope of the scriptblock. This is why your problem remained despite the correct advice you got on the Microsoft forums.
PS C:\> $ms = 100
PS C:\> $job = Start-Job -ScriptBlock { Start-Sleep -Milliseconds $ms }
PS C:\> $job | Wait-Job | Receive-Job
Cannot validate argument on parameter 'Milliseconds'. The argument is null,
empty, or an element of the argument collection contains a null value.
Supply a collection that does not contain any null values and then try the
command again.
+ CategoryInfo : InvalidData: (:) [Start-Sleep], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.PowerShell.Commands.StartSleepCommand
+ PSComputerName : localhost
You have three options to deal with this:
Define the variable inside the script block:
PS C:\> $job = Start-Job -ScriptBlock {
>> $ms = 100
>> $ms
>> Start-Sleep -Milliseconds $ms
>> }
>>
PS C:\> $job | Wait-Job | Receive-Job
100
Use the using scope modifier to get the local variable:
PS C:\> $ms = 100
PS C:\> $job = Start-Job -ScriptBlock {
>> $using:ms
>> Start-Sleep -Milliseconds $using:ms
>> }
>>
PS C:\> $job | Wait-Job | Receive-Job
100
Pass the variable into the scriptblock as an argument:
PS C:\> $ms = 100
PS C:\> $job = Start-Job -ScriptBlock {
>> param($ms)
>> $ms
>> Start-Sleep -Milliseconds $ms
>> } -ArgumentList $ms
>>
PS C:\> $job| Wait-Job | Receive-Job
100
Bottom line: replace
Start-Sleep -ms $sleepIntervalInMilliSeconds
with
Start-Sleep -Milliseconds $using:sleepIntervalInMilliSeconds
and the problem will disappear.