Prerequisites
Steps to reproduce
The PowerShell session crash occurs if you remove one of the child jobs from a ForEach-Object -Parallel job:
- Start a new PowerShell 7.5.x or 7.6.0 session
- Run:
# Create a parallel job with multiple child jobs that each sleep for a bit
$j = 0..20 | ForEach-Object -Parallel {
$r = Get-Random -Minimum 5 -Maximum 15
Start-Sleep $r
$r
} -AsJob
# Obtain the ChildJobs collection
$x = [Collections.Generic.List[Management.Automation.Job]]$j.ChildJobs
# And remove one entry while the jobs are still starting
$x.RemoveAt(15)Note: Using the random 5–15 second delay keeps the job in “starting” long enough to hit the exception.
Affected PowerShell versions: 7.5.3, latest build of 7.6.0 from main (didn't test on 7.4.x)
Tested on: Windows 11 25H2 x64.
Stack trace
An error has occurred that was not properly handled. Additional information is shown below. The PowerShell process will exit.
Unhandled exception. System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.Collections.Generic.List`1.Enumerator.MoveNext()
at System.Management.Automation.PSTasks.PSTaskJob.<Start>b__16_0(Object _) in D:\DEVELOPMENT\PowerShellCore\src\System.Management.Automation\engine\hostifaces\PSTask.cs:line 1140
at System.Threading.QueueUserWorkItemCallback.Execute()
at System.Threading.ThreadPoolWorkQueue.Dispatch()
The stack trace indicates the crash occurs inside PSTaskJob.Start on a ThreadPool callback while enumerating an internal List<T>. Mutating the ChildJobs list at the same time invalidates that enumerator, producing InvalidOperationException which is not caught and bubbles up, terminating the process.
Expected behavior
PowerShell should not terminate.
Either:
- Removing the child job succeeds safely, or
- The operation is rejected with a normal (catchable) error, or
- ChildJobs is exposed as read-only to user code.
Actual behavior
An error has occurred that was not properly handled. Additional information is shown below. The PowerShell process will exit.
Unhandled exception. System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.Collections.Generic.List`1.Enumerator.MoveNext()
at System.Management.Automation.PSTasks.PSTaskJob.<Start>b__16_0(Object _) in D:\DEVELOPMENT\PowerShellCore\src\System.Management.Automation\engine\hostifaces\PSTask.cs:line 1140
at System.Threading.QueueUserWorkItemCallback.Execute()
at System.Threading.ThreadPoolWorkQueue.Dispatch()
Error details
N/A – the session terminates due to an unhandled exception before Get-Error can be run.
Environment data
Name Value
---- -----
PSVersion 7.6.0-preview-4
PSEdition Core
GitCommitId 7.6.0-preview-4-168-gd5267d2ee661695e2dab15fdb651b4e23cd0503f
OS Microsoft Windows 10.0.26200
Platform Win32NT
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0, 5.0, 5.1, 6.0, 7.0}
PSRemotingProtocolVersion 2.4
SerializationVersion 1.1.0.1
WSManStackVersion 3.0Visuals
Prerequisites
Steps to reproduce
The PowerShell session crash occurs if you remove one of the child jobs from a
ForEach-Object -Paralleljob:Note: Using the random 5–15 second delay keeps the job in “starting” long enough to hit the exception.
Affected PowerShell versions: 7.5.3, latest build of 7.6.0 from main (didn't test on 7.4.x)
Tested on: Windows 11 25H2 x64.
Stack trace
The stack trace indicates the crash occurs inside
PSTaskJob.Starton aThreadPoolcallback while enumerating an internalList<T>. Mutating the ChildJobs list at the same time invalidates that enumerator, producingInvalidOperationExceptionwhich is not caught and bubbles up, terminating the process.Expected behavior
Actual behavior
Error details
N/A – the session terminates due to an unhandled exception before Get-Error can be run.Environment data
Visuals