How to Support Jobs

Article
09/23/2021

This example shows how to support jobs when you write cmdlets. If you want users to run your cmdlet as a background job, you must include the code described in the following procedure. For more information about background jobs, see Background Jobs.

To support jobs

Define an AsJob switch parameter so that the user can decide whether to run the cmdlet as a job.

The following example shows an AsJob parameter declaration.
```
[Parameter()]
public SwitchParameter AsJob
{
  get { return asjob; }
  set { asjob = value; }
}
private bool asjob;
```
Create an object that derives from the System.Management.Automation.Job class. This object can be a custom job object or one of the job objects provided by Windows PowerShell, such a System.Management.Automation.Pseventjob object.

The following example shows a custom job object.
```
private SampleJob job = new SampleJob("Get-ProcAsJob");
```

In a record processing method, add an if statement to detect whether the cmdlet should run as a job. The following code uses the System.Management.Automation.Cmdlet.ProcessRecord method.

protected override void ProcessRecord()
{
  if (asjob)
  {
    // Add the job definition to the job repository,
    // return the job object, and then create the thread
    // used to run the job.
    JobRepository.Add(job);
    WriteObject(job);
    ThreadPool.QueueUserWorkItem(WorkItem);
  }
  else
  {
    job.ProcessJob();
    foreach (PSObject p in job.Output)
    {
      WriteObject(p);
    }
  }
}

For custom job objects, implement the job class.

private class SampleJob : Job
{
  internal SampleJob(string command)
      : base(command)
  {
    SetJobState(JobState.NotStarted);
  }
  public override string StatusMessage
  {
    get { throw new NotImplementedException(); }
  }

  public override bool HasMoreData
  {
    get
    {
      return hasMoreData;
    }
  }
  private bool hasMoreData = true;

  public override string Location
  {
    get { throw new NotImplementedException(); }
  }

  public override void StopJob()
  {
    throw new NotImplementedException();
  }

  internal void ProcessJob()
  {
    SetJobState(JobState.Running);
    DoProcessLogic();
    SetJobState(JobState.Completed);
  }

  // Retrieve the processes of the local computer.
  void DoProcessLogic()
  {
    Process[] p = Process.GetProcesses();

    foreach (Process pl in p)
    {
      Output.Add(PSObject.AsPSObject(pl));
    }
    Output.Complete();
  } // End DoProcessLogic.
} // End SampleJob class.

If the cmdlet performs the work, call the System.Management.Automation.Cmdlet.WriteObject method to return a process object to the pipeline. If the work is performed as a job, add child job to the job.

void DoProcessLogic(bool asJob)
{
  Process[] p = Process.GetProcesses();

  foreach (Process pl in p)
  {
    if (!asjob)
    {
      WriteObject(pl);
    }
    else
    {
      job.ChildJobs[0].Output.Add(PSObject.AsPSObject(pl));
    }
  }
} // End DoProcessLogic.

Example

The following sample code shows the code for a Get-Proc cmdlet that can retrieve processes internally or by using a background job.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Management.Automation;  // Windows PowerShell namespace.
using System.Threading;              // Thread pool namespace for posting work.
using System.Diagnostics;            // Diagnostics namespace for retrieving
                                     // process objects.

// This sample shows a cmdlet whose work can be done by the cmdlet or by using
// a background job. Background jobs are executed in their own thread,
// independent of the pipeline thread in which the cmdlet is executed.
//
// To load this cmdlet, create a module folder and copy the GetProcessSample06.dll
// assembly into the module folder. Make sure that the path to the module folder
// is added to the $PSModulePath environment variable.
// Module folder path:
//    user/documents/WindowsPowerShell/modules/GetProcessSample06
//
// To import the module, run the following command: Import-Module GetProcessSample06.
// To test the cmdlet, run the following command: Get-Proc -name <process name>
//

//
namespace Microsoft.Samples.PowerShell.Commands
{
  /// <summary>
  ///  This cmdlet retrieves process internally or returns
  ///  a job that retrieves the processes.
  /// </summary>
  [Cmdlet(VerbsCommon.Get, "Proc")]
  public sealed class GetProcCommand : PSCmdlet
  {

    #region Parameters
    /// <summary>
    /// Specify the Name parameter. This parameter accepts
    /// process names from the command line.
    /// </summary>
    [Parameter(
               Position = 0,
               ValueFromPipeline = true,
               ValueFromPipelineByPropertyName = true)]
    [ValidateNotNullOrEmpty]
    public string[] Name
    {
      get { return processNames; }
      set { processNames = value; }
    }
    private string[] processNames;

    /// <summary>
    /// Specify the AsJob parameter. This parameter indicates
    /// whether the cmdlet should retrieve the processes internally
    /// or return a Job object that retrieves the processes.
    /// </summary>
    [Parameter()]
    public SwitchParameter AsJob
    {
      get { return asjob; }
      set { asjob = value; }
    }
    private bool asjob;

    #endregion Parameters

    #region Cmdlet Overrides

    // Create a custom job object.
    private SampleJob job = new SampleJob("Get-ProcAsJob");

    /// <summary>
    /// Determines if the processes should be retrieved
    /// internally or if a Job object should be returned.
    /// </summary>
    protected override void ProcessRecord()
    {
      if (asjob)
      {
        // Add the job definition to the job repository,
        // return the job object, and then create the thread
        // used to run the job.
        JobRepository.Add(job);
        WriteObject(job);
        ThreadPool.QueueUserWorkItem(WorkItem);
      }
      else
      {
        job.ProcessJob();
        foreach (PSObject p in job.Output)
        {
          WriteObject(p);
        }
      }
    }
    #endregion Overrides

    // Implement a custom job that derives
    // from the System.Management.Automation.Job class.
    private class SampleJob : Job
    {
      internal SampleJob(string command)
          : base(command)
      {
        SetJobState(JobState.NotStarted);
      }
      public override string StatusMessage
      {
        get { throw new NotImplementedException(); }
      }

      public override bool HasMoreData
      {
        get
        {
          return hasMoreData;
        }
      }
      private bool hasMoreData = true;

      public override string Location
      {
        get { throw new NotImplementedException(); }
      }

      public override void StopJob()
      {
        throw new NotImplementedException();
      }

      internal void ProcessJob()
      {
        SetJobState(JobState.Running);
        DoProcessLogic();
        SetJobState(JobState.Completed);
      }

      // Retrieve the processes of the local computer.
      void DoProcessLogic()
      {
        Process[] p = Process.GetProcesses();

        foreach (Process pl in p)
        {
          Output.Add(PSObject.AsPSObject(pl));
        }
        Output.Complete();
      } // End DoProcessLogic.
    } // End SampleJob class.

    void WorkItem(object dummy)
    {
       job.ProcessJob();
    }

    // Display the results of the work. If not a job,
    // process objects are returned. If a job, the
    // output is added to the job as a child job.
    void DoProcessLogic(bool asJob)
    {
      Process[] p = Process.GetProcesses();

      foreach (Process pl in p)
      {
        if (!asjob)
        {
          WriteObject(pl);
        }
        else
        {
          job.ChildJobs[0].Output.Add(PSObject.AsPSObject(pl));
        }
      }
    } // End DoProcessLogic.
  } //End GetProcCommand
}

How to Support Jobs

To support jobs

Example

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