并行和异步 C#

Question

I'm writing a Console Application in C# that takes an array of videos and transcode it as long a new GPU is free to use. The machine where the app will run has two GPUs. But I'm really having a hard time how to build this up. The method that does the job is FireTranscode()

private void FireTranscode(int counter)
  {
   Random rand = new Random();
   int gpu;

   lock (thisLock)
   {
    gpu = PickGPU(0) == true ? 0 : 1;
    GPU[gpu] = false;
    if (gpu == 0) { gpuZero += 1; } else { gpuOne += 1; };
    Thread.Sleep(rand.Next(1, 5));
    videos -= 1;
   }

   Console.WriteLine($"Transconding on {gpu} using thread: {Thread.CurrentThread.ManagedThreadId}  {transcodeArray[Convert.ToInt32(counter), 2]}");
    GPU[gpu] = true;
}

and it's triggered by ManageTranscode()

private async void ManageTrancode()
  {
   for(counter=0; counter < videos; counter++)
   {
    if (GPU[0] == false & GPU[1] == false)
    {
     await Task.WhenAny(transcodeList);
    }
    else
    {
     transcodeList.Add(Task.Factory.StartNew(() => FireTranscode(counter)));
    }
   }
  }

It suppose to call the FireTranscode followed by the parameter counter, 40 times async (value of videos variable), and in case both GPU ( static Dictionary<int, bool> GPU = new Dictionary<int, bool> { { 0, true }, { 1, true } }; are in use (=false) it should wait until any task finishes and free for use (=true).

I'm trying to learn how to use it correctly and I would appreciate some tips and help how to achieve this. Thank you.

Answer 1

You can simplify your logic and also make it more extensible in terms of available GPU by using below code. It uses SemaphoreSlim (also mentioned by @Poul Bak) which allows degree of parallelism by defined parameters.

Also, I've refactored your code to have GPU as class (you can use Struct too).

private object lockObj = new object();
private List<GPU> availableGPUs = List<GPU>() { /* initialize GPUs here */}; 
private int AvailableGPUCount { get { return availableGPUs.Count(); } }
private async void ManageTrancode()
{
    int maxThread = AvailableGPUCount;
    SemaphoreSlim lockSlim = new SemaphoreSlim(maxThread, maxThread);
    for(int counter = 0; counter < videos; counter++)
    {
        await lockSlim.WaitAsync();
        await Trancode();
        lockSlim.Release();
    }
}


private async Task Trancode()
{
    GPU gpu = GetAndLockGPU(); 
    // await <<Run actual trancode here>>
    ReleaseGPU(gup.Id);
}

private GPU GetAndLockGPU()
{
    GPU gpu = null;
    lock (lockObj)
    {
        gpu = availableGPUs.First(g => g.IsAvailable);
        gpu.IsAvailable = false;
    }
    
    return gpu; 
}

private void ReleaseGPU(int gpuId)
{
    lock (lockObj)
    {
        availableGPUs.First(g => g.Id == gpuId).IsAvailable = true;
    }
}

private class GPU
{
    public int Id {get; set;}
    public bool IsAvailable {get; set;} = true;
}