parallel still not working for some reason

gistfile1.txt

module Program

#light

open System.Threading
open StructureMap
open BrewTelligence.Domain
open BrewTelligence.Search.Indexing
open BrewTelligence.ApplicationServices
open BrewTelligence.ApplicationServices.Messaging

printfn "indexing in: %s" BrewTelligence.Search.FileSystem.IndexDirectory.Path;

ObjectFactory.Initialize(fun x -> x.AddRegistry (new SearchRegistry()))

let write<'T> (item:'T) =
    printfn "writing: %A" item
    ObjectFactory.GetAllInstances<Indexer<'T>>() |> Seq.iter (fun idxr -> idxr.Index item)
        
let indexActions<'T when 'T: not struct and 'T:null and 'T:equality> =
    let p = QueueProvider<'T>.Create()
    seq {
        while true do
            let obj = p.Dequeue()
            if obj = null then 
                yield None
                Thread.Sleep 500 //this necessary?
            else 
                yield Some(async { write obj })
    }

try
    indexActions<Yeast>
        |> Seq.merge indexActions<Addition>
        |> Seq.merge indexActions<Hop>
        |> Seq.merge indexActions<Malt>
        |> Seq.merge indexActions<Recipe>
        |> OptionSeq.unwrapAndDiscardEmpty
        //|> Async.Parallel //not sure why this isn't working
        |> Seq.iter Async.RunSynchronously
        |> ignore

finally
    SearchRegistry.DeRegister()