A demonstration of using Write-Progress in a thread-safe way inside Foreach-Parallel

Get-GroupCompareInfo.ps1

using namespace System.Collections.Concurrent
using namespace System.Collections.Generic

function Get-GroupCompareInfo {
  [OutputType([SortedDictionary[string, string[]]])]
  <#
  .SYNOPSIS
  Creates a simple dictionary useful for comparing groups across tenants
  .DESCRIPTION
  This boils down a list of groups supplied by GroupID to a dictionary containing the unique alias of the group and the left-side UPN of the users
  This is useful when comparing to another directory to make sure the groups are the same
  #>
  [CmdletBinding()]
  param(
    [Parameter(ValueFromPipeline)][Guid]$GroupId
  )
  begin {
    #We collect the group Ids so we can process them in parallel
    [Hashset[Guid]]$groupIds = @()
  }
  process {
    $isUnique = $groupIds.Add($GroupId)
    if (-not $isUnique) { Write-Warning "$groupId is a duplicate entry, skipping..." }
  }
  end {
    #Track progress
    [int]$progressIndicator = 0
    [int]$progressId = Get-Random
    $progressIndicatorRef = [ref]::new($progressIndicator)
    #We have to do a lot of lookups of members, this will allow for a simple deduplication of those members to improve performance
    $memberCache = [ConcurrentDictionary[guid, string]]::new()
    #A simple table with the mail alias of the group and the shortname of the members. This is for easy comparison with the other tenant
    $groupMembers = [ConcurrentDictionary[string, string[]]]::new()

    Write-Progress -Id $progressId -Activity 'Gathering Group Comparison Info'
    $groupIds | ForEach-Object -Verbose -Throttle 10 -Parallel {
      param (
        $memberCache = $USING:memberCache,
        $groupMembers = $USING:groupMembers,
        $parentProgressId = $USING:progressId,
        $progressIndicatorRef = $USING:progressIndicatorRef,
        $groupIdCount = $USING:groupIds.Count
      )
      #Optimize load time by only importing the functions we need
      Import-Module Microsoft.Graph.Users, Microsoft.Graph.Groups -Function 'Get-MgUser', 'Get-MgGroup', 'Get-MgGroupMember'
      $progressParams = @{
        Id       = (Get-Random)
        ParentId = $parentProgressId
        Activity = 'Building Membership Table: ' + $PSItem
      }
      try {
        $DebugPreference = 'continue'
        [Guid]$groupId = $PSItem
        Write-Progress @progressParams -Status 'Getting Group Name'
        [String]$groupName = (Get-MgGroup -GroupId $groupId -Property mailNickname).mailNickname
        $progressParams.Activity = "Building Membership Table: $groupName ($PSItem)"
        [Guid[]]$memberIds = (Get-MgGroupMember -GroupId $groupId).id
        $i = 0
        $groupMembers[$groupName] = $memberIds | ForEach-Object {
          Write-Progress @progressParams -Status "Resolving $PSItem to Username" -PercentComplete ($i / $memberIds.count * 100)
          $cached = $memberCache.ContainsKey($PSItem)
          Write-Debug "$PSItem Cache $($cached ? 'Hit' : 'Miss')"
          $userResult = if ($cached) {
            Write-Output $memberCache[$PSItem]
          } else {
            [string]$username = (Get-MgUser -UserId $PSItem -Property userprincipalname).userprincipalname.split('@')[0]
            if (-not $username) { throw "User with GUID $PSItem doesnt exist. This is probably a bug" }
            $memberCache[$PSItem] = $username
            Write-Output $username
          }
          $i++
          return $userResult
        }
      } catch { throw } finally {
        Write-Progress @progressParams -Completed
        #Increment progress in a thread safe way
        [void][Threading.Interlocked]::Increment($progressIndicatorRef)
        Write-Progress -Id $parentProgressId -Activity 'Gathering Group Comparison Info' -Status "$groupName ($groupId) completed [$($progressIndicatorRef.Value) of $groupIdCount]" -PercentComplete ($progressIndicatorRef.Value / $groupIdCount * 100)
        Start-Sleep 10
      }
    }

    Write-Progress -Id $progressId -Activity 'Done' -Completed
    return [SortedDictionary[string, string[]]]$groupMembers
  }
}

Demo:

Capture.mp4