How to get a PID of Windows process called with $zf(-1,...)?

I don't know of any magic $zf/$zu function or API to do this. Looking at StackOverflow, a common approach seems to be parsing the output of "tasklist" filtered by executable name and/or window title.

Here's a classmethod to get the PIDs of all processes with a given executable name (Windows-only, of course):

Class DC.Demo.WindowsProcessList
{

ClassMethod GetPIDsByExecutable(pExecutable As %String = "", Output pPIDList As %List) As %Status
{
    Set tSC = $$$OK
    Set tFileCreated = 0
    Set pPIDList = ""
    Try {
        Set tSC = ##class(%Net.Remote.Utility).RunCommandViaZF("tasklist /V /FO CSV /NH",.tTempFileName,,,0)
        $$$ThrowOnError(tSC)
        Set tFileCreated = (tTempFileName '= "")
        Set tRowSpec = "ROW(ImageName VARCHAR(255),PID INT)"
        Set tResult = ##class(%SQL.Statement).%ExecDirect(,
            "call %SQL_Util.CSV(,?,?)",
            tRowSpec,tTempFileName)
        
        // For debugging (if tRowSpec changes):
        // Do tResult.%Display()
        
        If (tResult.%SQLCODE < 0) {
            Throw ##class(%Exception.SQL).CreateFromSQLCODE(tResult.%SQLCODE, tResult.%Message)
        }
        
        // Note: could instead call tResult.%NextResult() to get a result set with column names as properties.
        While tResult.%Next(.tSC) {
            $$$ThrowOnError(tSC)
            If ($ZConvert(tResult.%GetData(1),"L") = $ZConvert(pExecutable,"L")) {
                Set pPIDList = pPIDList_$ListBuild(tResult.%GetData(2))
            }
        }
        $$$ThrowOnError(tSC)
    } Catch e {
        Set tSC = e.AsStatus()
    }
    
    // Cleanup
    If tFileCreated {
        Do ##class(%Library.File).Delete(tTempFileName)
    }
    Quit tSC
}

}