Why does System.Diagnostic.Process#HandleCount exist?

[jpsnover]

Steps to reproduce

$a,$b = gps
$a.pstypenames

Expected behavior

System.Diagnostic.Process
System.Object

Actual behavior

System.Diagnostic.Process#HandleCount
System.Diagnostic.Process
System.Object

Environment data

jps> $a,$b = get-process                                                                                                              
jps> $a.pstypenames                                                                                                                   
System.Diagnostics.Process#HandleCount
System.Diagnostics.Process
System.Object
jps> $PSVersionTable                                                                                                                  

Name                           Value                                                                                                 
----                           -----                                                                                                 
PSVersion                      6.0.0-alpha                                                                                           
PSEdition                      Core                                                                                                  
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}                                                                               
BuildVersion                   3.0.0.0                                                                                               
GitCommitId                    v6.0.0-alpha.8                                                                                        
CLRVersion                                                                                                                           
WSManStackVersion              3.0                                                                                                   
PSRemotingProtocolVersion      2.3                                                                                                   
SerializationVersion           1.1.0.1        

[andyleejordan]

This is... an excellent question. I couldn't find HandleCount referenced anywhere but as fields in internal sources in .NET Core.

/cc @daxian-dbw

[daxian-dbw]

I remember it was because in remoting scenario the type definition on the client side expects the 'HandleCount' property when deserializing a Process object, and it will fail with exception when that property is not available. The noteproperty was added just to make sure all existing powershell client can work well in this case during remoting.

/cc @Francisco-Gamino

[SteveL-MSFT]

Making a change may break existing remoting scenarios particularly between WindowsPowerShell and PowerShell Core. Does not impact the functionality. Recommend no change.

[iSazonov]

I caught the Issue when writing Pester tests:

Get-Process | Export-Csv -Path $testfile -Force

#TYPE System.Diagnostics.Process#HandleCount
"HandleCount","Name","SI","Handles","VM","WS","PM","NPM","Path","Company","CPU","FileVersion","ProductVersion","Description","Product","__NounName","SafeHandle","BasePriority","ExitCode","HasExited","ExitTime","Id","MachineName","MaxWorkingSet","MinWorkingSet","Modules","NonpagedSystemMemorySize64","PagedMemorySize64","PagedSystemMemorySize64","PeakPagedMemorySize64","PeakWorkingSet64","PeakVirtualMemorySize64","PriorityBoostEnabled","PriorityClass","PrivateMemorySize64","ProcessName","ProcessorAffinity","SessionId","StartInfo","Threads","VirtualMemorySize64","EnableRaisingEvents","StandardInput","StandardOutput","StandardError","WorkingSet64","MainModule","PrivilegedProcessorTime","StartTime","TotalProcessorTime","UserProcessorTime"
"0","ApplicationFrameHost","3","0","2199252946944","20496384","12066816","17936","C:\Windows\system32\ApplicationFrameHost.exe",,"0.28125",,,,,"Process","Microsoft.Win32.SafeHandles.SafeProcessHandle","8",,"False",,"5776",".","1413120","204800","System.Diagnostics.ProcessModuleCollection","17936","12066816","328544","13901824","27131904","2199287431168","True","Normal","12066816","ApplicationFrameHost","15","3",,"System.Diagnostics.ProcessThreadCollection","2199252946944","False",,,,"20496384","System.Diagnostics.ProcessModule (ApplicationFrameHost.exe)","00:00:00.1562500","10/17/2016 6:13:36 AM","00:00:00.2812500","00:00:00.1250000"

I believe that this is not exactly what is expected.

[iSazonov]

@daxian-dbw and @SteveL-MSFT Could you please comment on this?

[daxian-dbw]

@iSazonov The HandleCount was kept there just to make sure when running $p = Invoke-Command -Session $sn { Get-Process -Id $pid } on a down-level powershell client targeting a powershell core on server side, it doesn't throw exception on the down-level powershell client.

Object like System.Diagnostics.Process is deserialized to Deserialized.System.Diagnostics.Process when transferring from server to client. Type Deserialized.System.Diagnostics.Process is defined in types.ps1xml, and if you inspect the definition, you will see the property HandleCount is present, and it's expected when powershell deserializes the Process object. The missing of such property will cause an exception to be thrown on the client side.

We certainly can change types.ps1xml and powershell core to make it not expect the HandleCount property when deserializing Process objects from server. However, that won't help the existing down-level powershell instances out there, and we still want the down-level PS client to be able to remote to powershell core without problems. That's why we kept the HandleCount property, even though it's meaningless in CoreCLR.

[iSazonov]

@daxian-dbw Thanks for the great in-depth explanation. This clearly. But my question is easier. My question is specifically about Export-Csv behavior.
Why do Export-Csv write "Type#HandleCount" in Powershell 6.0 while the expected behavior is to write "Type"? I believe it is bug and regression.

In Powershell 5.0:

$a= Get-Process -ComputerName comp
$a[0].psobject

ImmediateBaseObject : System.Diagnostics.Process (avagent)
BaseObject          : System.Diagnostics.Process (avagent)
TypeNames           : {System.Diagnostics.Process, System.ComponentModel.Component, System.MarshalByRefObject,
                      System.Object}

In Powershell 6.0:

$a= Get-Process -ComputerName comp
$a[0].psobject

ImmediateBaseObject : System.Diagnostics.Process (ApplicationFrameHost)
BaseObject          : System.Diagnostics.Process (ApplicationFrameHost)
TypeNames           : {System.Diagnostics.Process#HandleCount, System.Diagnostics.Process, System.Object}

In code Export-Csv get TypeNames[0]. Perhaps we need to take BaseObject ? Or remove #HandleCount from TypeNames[0]? Or take TypeNames[1] if TypeNames[0] contains "#HandleCount"?

[lzybkr]

It seems somewhat useful to know the HandleCount property was synthesized and therefore not useful, e.g. we could change the display of ProcessInfo to not show the HandleCount property at all if the typename is ProcessInfo#HandleInfo.

[iSazonov]

@lzybkr If this will fix both (@jpsnover and my) issues, maybe should reopen the Issue?

[iSazonov]

According to #2207 it is CoreCLR bug that is waiting for a fix.

[SteveL-MSFT]

Recommendation is to change the formatting to not show this as it's not useful to admin and the property is still available for compat reasons

[iSazonov]

Where should it be fixed? Maybe here in Process.cs

             // In CoreCLR, the System.Diagnostics.Process.HandleCount property does not exist. 
             // I am adding a note property HandleCount and temporarily setting it to zero. 
             // This issue will be fix for RTM and it is tracked by 5024994: Get-process does not populate the Handles field. 
             PSMemberInfo hasHandleCount = processAsPsobj.Properties["HandleCount"]; 
             if (hasHandleCount == null) 
             { 
                 PSNoteProperty noteProperty = new PSNoteProperty("HandleCount", 0); 
                 processAsPsobj.Properties.Add(noteProperty, true); 
                 processAsPsobj.TypeNames.Insert(0, "System.Diagnostics.Process#HandleCount"); 
             } 

remove processAsPsobj.TypeNames.Insert(0, "System.Diagnostics.Process#HandleCount");
I have not found using this in code anywhere.

[SteveL-MSFT]

@iSazonov the suggestion is to change the formatter and keep the code for compat reasons. this way it doesn't show up for the interactive user as it's not really useful anyways (IMHO), but still available on the object (on Windows for some dev scenarios). while looking for the code, I already made a fix and will submit a PR

[iSazonov]

@SteveL-MSFT Clear! Thanks!