Import-CsvAsync

Function New-Runspace([string]$Name, [string]$Path, [hashtable]$SyncHash, [System.Collections.Generic.List[object]]$Jobs)
{
    $importScript = {
        param ([string]$Name, [string]$Path)
        $import.Add($Name, (Import-Csv -Path $Path))
    }

    $runspace = [runspacefactory]::CreateRunspace()
    $runspace.ApartmentState = "STA"
    $runspace.ThreadOptions = "ReuseThread"
    $runspace.Open()
    $runspace.SessionStateProxy.SetVariable("import", $SyncHash)

    $ps = [powershell]::Create().AddScript($importScript).AddParameter("Name", $Name).AddParameter("Path", $Path)
    $ps.Runspace = $runspace
    $async = [pscustomobject]@{
        PowerShell = $ps
        Runspace = $ps.BeginInvoke()
    }
    $Jobs.Add($async) | Out-Null
}

Function Import-CsvAsync
{
    [CmdletBinding()]
    [OutputType([hashtable])]
    param
    (
        [Parameter(Mandatory=$true, Position = 0)]
        [string[]] $FilePath,

        [Parameter(Mandatory=$false)]
        [ValidateRange(1, [int]::MaxValue)]
        [int] $CheckIntervalInMS = 1000
    )
    $import = [hashtable]::Synchronized(@{})
    $import.Errors = New-Object 'System.Collections.Generic.List[System.Management.Automation.ErrorRecord]'

    $jobsList = New-Object System.Collections.Generic.List[object] -ArgumentList $FilePath.Length
    foreach ($file in $FilePath)
    {
        $fileInfo = Get-ChildItem -Path $file
        $nsArgs = @{
            Name = $fileInfo.BaseName
            Path = $fileInfo.FullName
            SyncHash = $import
            Jobs = $jobsList
        }
        New-Runspace @nsArgs
    }

    while ($jobsList.Count -gt 0)
    {
        for ($i = $jobsList.Count - 1; $i -ge 0; $i--)
        {
            $job = $jobsList[$i]
            if ($job.Runspace.IsCompleted)
            {
                $job.PowerShell.EndInvoke($job.Runspace) | Out-Null
                if ($job.PowerShell.HadErrors)
                {
                    $import.Errors.AddRange($job.PowerShell.Streams.Error)
                }
                $job.PowerShell.Dispose()
                $jobsList.Remove($job) | Out-Null
            }
        }
        Start-Sleep -Milliseconds $CheckIntervalInMS
    }
    $import
}