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Avoid mutable ChildJobs enumeration in PSTaskJob #27512

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Avoid mutable ChildJobs enumeration in PSTaskJob #27512

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f71a02e
Avoid mutable ChildJobs enumeration in PSTaskJob
KirtiRamchandani May 24, 2026
dad6d60
Use ChildJobs snapshots in PSTaskJob
KirtiRamchandani May 24, 2026
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9 changes: 5 additions & 4 deletions src/System.Management.Automation/engine/hostifaces/PSTask.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Management.Automation.Host;
using System.Management.Automation.Language;
using System.Management.Automation.Remoting.Internal;
Expand Down Expand Up @@ -1056,7 +1057,7 @@ public override bool HasMoreData
{
get
{
foreach (var childJob in ChildJobs)
foreach (var childJob in ChildJobs.ToArray())
{
Comment on lines +1060 to 1061
if (childJob.HasMoreData)
Comment on lines +1060 to 1062
{
Expand Down Expand Up @@ -1137,9 +1138,9 @@ internal void Start()
System.Threading.ThreadPool.QueueUserWorkItem(
(_) =>
{
foreach (var childJob in ChildJobs)
foreach (PSTaskChildJob childJob in ChildJobs.ToArray())
{
_taskPool.Add((PSTaskChildJob)childJob);
_taskPool.Add(childJob);
}
Comment on lines 1138 to 1144

_taskPool.Close();
Expand All @@ -1162,7 +1163,7 @@ private void HandleTaskPoolComplete(object sender, EventArgs args)

// Final state will be 'Complete', only if all child jobs completed successfully.
JobState finalState = JobState.Completed;
foreach (var childJob in ChildJobs)
foreach (var childJob in ChildJobs.ToArray())
{
if (childJob.JobStateInfo.State != JobState.Completed)
{
Expand Down
38 changes: 38 additions & 0 deletions test/powershell/Modules/Microsoft.PowerShell.Utility/Foreach-Object-Parallel.Tests.ps1
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Expand Up @@ -486,6 +486,44 @@ Describe 'ForEach-Object -Parallel -AsJob Basic Tests' -Tags 'CI' {
$job | Wait-Job | Remove-Job
}

It 'Does not crash when the ChildJobs collection is mutated while a parallel job starts' {
$testScript = Join-Path $TestDrive 'Mutate-ChildJobs.ps1'
$stdoutPath = Join-Path $TestDrive 'stdout.txt'
$stderrPath = Join-Path $TestDrive 'stderr.txt'
Set-Content -LiteralPath $testScript -Value @'
$job = 0..20 | ForEach-Object -AsJob -Parallel {
Start-Sleep -Milliseconds 300
$_
} -ThrottleLimit 2

Start-Sleep -Milliseconds 100
$deadline = [DateTime]::UtcNow.AddSeconds(30)
while ($job.ChildJobs.Count -le 15 -and [DateTime]::UtcNow -lt $deadline) {
Start-Sleep -Milliseconds 100
}

if ($job.ChildJobs.Count -le 15) {
throw "Timed out waiting for child jobs to be created."
}

$job.ChildJobs.RemoveAt(15)

$job | Wait-Job -Timeout 30 | Out-Null
$job | Remove-Job -Force
'@

$powershell = Join-Path -Path $PSHOME -ChildPath "pwsh"
$process = Start-Process -FilePath $powershell -ArgumentList @(
'-NoLogo'
'-NoProfile'
'-NonInteractive'
'-File'
$testScript
) -RedirectStandardOutput $stdoutPath -RedirectStandardError $stderrPath -Wait -PassThru

Comment on lines +522 to +523
$process.ExitCode | Should -Be 0
}

It 'Verifies dollar underbar variable' {

$expected = 1..10
Expand Down