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Allow for nested ThreadJobs by resetting the pool object #59
Description
Summary of the new feature / enhancement
ThreadJobs become a problem if you want to use them throughout a module; you have to be careful that you never create a ThreadJob within something else running within a ThreadJob, because it has a global queue.
If you are executing any number of tasks over your throttle limit, and then start a new job within one of those, they can deadlock because the pool is full.
So something as simple as this will never return:
$jobs = 1..5 | %{
Start-ThreadJob {
Start-Sleep -Seconds 1
Start-ThreadJob {
Start-Sleep -Seconds 1
} | Wait-Job | Receive-Job
} -Throttle 5
}
$jobs | Wait-Job
Ideally you should have the option to avoid this.
Proposed technical implementation details (optional)
If you add a Restart-ThreadJob cmdlet that will reset the pool, you can now control when you want to create a fresh pool. This guards against that kind of deadlock.
$jobs = 1..5 | %{
Start-ThreadJob {
Start-Sleep -Seconds 1
Restart-ThreadJob
Start-ThreadJob {
Start-Sleep -Seconds 1
} | Wait-Job | Receive-Job
} -Throttle 5
}
$jobs | Wait-Job
Works. Of course, you now have 1 pool of 5 and another 5 pools of 5 (the default), but it doesn't hang. You get to control it.
diff --git a/src/Microsoft.PowerShell.ThreadJob.psd1 b/src/Microsoft.PowerShell.ThreadJob.psd1
index 7b127d4..342009b 100644
--- a/src/Microsoft.PowerShell.ThreadJob.psd1
+++ b/src/Microsoft.PowerShell.ThreadJob.psd1
@@ -44,7 +44,7 @@ number of jobs drops below the throttle limit.
PowerShellVersion = '5.1'
# Cmdlets to export from this module
-CmdletsToExport = 'Start-ThreadJob'
+CmdletsToExport = 'Start-ThreadJob', 'Restart-ThreadJob'
# Private data to pass to the module specified in RootModule/ModuleToProcess. This may also contain a PSData hashtable with additional module metadata used by PowerShell.
PrivateData = @{
diff --git a/src/code/Microsoft.PowerShell.ThreadJob.cs b/src/code/Microsoft.PowerShell.ThreadJob.cs
index c967e9d..ff45cf9 100644
--- a/src/code/Microsoft.PowerShell.ThreadJob.cs
+++ b/src/code/Microsoft.PowerShell.ThreadJob.cs
@@ -142,6 +142,31 @@ namespace Microsoft.PowerShell.ThreadJob
#endregion
}
+ [Cmdlet(VerbsLifecycle.Restart, "ThreadJob")]
+ public sealed class RestartThreadJobCommand : PSCmdlet
+ {
+ #region Overrides
+
+ protected override void BeginProcessing()
+ {
+ base.BeginProcessing();
+
+ ThreadJob.Reset();
+ }
+
+ protected override void ProcessRecord()
+ {
+ base.ProcessRecord();
+ }
+
+ protected override void EndProcessing()
+ {
+ base.EndProcessing();
+ }
+
+ #endregion
+ }
+
public sealed class ThreadJobSourceAdapter : JobSourceAdapter
{
#region Members
@@ -491,6 +516,8 @@ namespace Microsoft.PowerShell.ThreadJob
private static ThreadJobQueue s_JobQueue;
+ private static object _syncObject = new object();
+
#endregion
#region Properties
@@ -508,10 +535,18 @@ namespace Microsoft.PowerShell.ThreadJob
#region Constructors
+ public static void Reset()
+ {
+ lock (_syncObject)
+ {
+ s_JobQueue = new ThreadJobQueue(5);
+ }
+ }
+
// Constructors
static ThreadJob()
{
- s_JobQueue = new ThreadJobQueue(5);
+ Reset();
if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
{
Assembly assembly = typeof(PSObject).Assembly;
@@ -806,7 +841,10 @@ namespace Microsoft.PowerShell.ThreadJob
/// <param name="throttleLimit"></param>
public static void StartJob(ThreadJob job, int throttleLimit)
{
- s_JobQueue.EnqueueJob(job, throttleLimit);
+ lock (_syncObject)
+ {
+ s_JobQueue.EnqueueJob(job, throttleLimit);
+ }
}
/// <summary>
If you want to implement it in some better way, go ahead. This is just something.
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