Wrap the dotnet thread pool with a Go inspired "waitgroup"

ThreadPoolWrapper.fs

open System.Threading

type WorkerGroup =
    { wait: unit -> unit
      release: unit -> unit
      waitGroup: unit -> unit }

let initWorkerGroup count =
    let semaphore = new SemaphoreSlim(count)

    { wait = fun () -> semaphore.Wait()
      release = fun () -> semaphore.Release() |> ignore
      waitGroup =
        fun () ->
            for _ in 1..count do
                semaphore.Wait() }

let queueWork workerGroup data action =
    workerGroup.wait ()

    let actionCallback _ =
        try
            action data
        finally
            workerGroup.release ()

    ThreadPool.QueueUserWorkItem(actionCallback, data) |> ignore

printfn "Starting"

let workers = 50
let workerGroup = initWorkerGroup workers

for i in 1..workers do
    queueWork workerGroup i (fun data ->
        Thread.Sleep 1000
        printfn "Thread %i: had worker-number %i" (Thread.GetCurrentProcessorId()) data)

workerGroup.waitGroup ()

printfn "Main done"