C#•2y ago

❔ ❔ ❔ SemaphoreSlim that can be entered without waiting

Hello, I am trying to find way to easily control how much threads can enter semaphore. I need something like SemaphoreSlim but that supports entering without waiting or Releasing with minus values. For example:

await semaphoreSlim.WaitAsync();
try
{
  if (something)
    semaphoreSlim.Release(10); // allows 10 more threads to enter
  else
    semaphoreSlim.Release(-10); // limits 10 threads from entering
}
finally
{
  semaphoreSlim.Release();
}

await semaphoreSlim.WaitAsync();
try
{
  if (something)
    semaphoreSlim.Release(10); // allows 10 more threads to enter
  else
    semaphoreSlim.Release(-10); // limits 10 threads from entering
}
finally
{
  semaphoreSlim.Release();
}

I there any built in object to do it? I really don't want to implement such thing myself.

2 Replies

kuba_z2•2y ago

Ok, I had to write it myself:

internal class AdjustableSemaphoreSlim
{
    private readonly object _lock = new();
    private readonly LinkedList<TaskCompletionSource> _sources = new();
    private int _count;

    public AdjustableSemaphoreSlim(int initialCount)
    {
        _count = initialCount;
    }

    public void Release()
    {
        lock (_lock)
        {
            _count++;
            if (_sources.Count != 0)
            {
                _sources.First!.Value.SetResult();
                _sources.RemoveFirst();
            }
        }
    }

    public void Release(int count)
    {
        lock (_lock)
        {
            _count += count;
            for (int i = Math.Min(_sources.Count, count); i > 0; i--)
            {
                _sources.First!.Value.SetResult();
                _sources.RemoveFirst();
            }
        }
    }

    public void Enter(int count)
    {
        lock (_lock)
            _count -= count;
    }

    public Task WaitAsync()
    {
        lock (_lock)
        {
            if (--_count >= 0)
                return Task.CompletedTask;
            else
            {
                TaskCompletionSource source = new();
                _sources.AddLast(source);
                return source.Task;
            }
        }
    }
}

internal class AdjustableSemaphoreSlim
{
    private readonly object _lock = new();
    private readonly LinkedList<TaskCompletionSource> _sources = new();
    private int _count;

    public AdjustableSemaphoreSlim(int initialCount)
    {
        _count = initialCount;
    }

    public void Release()
    {
        lock (_lock)
        {
            _count++;
            if (_sources.Count != 0)
            {
                _sources.First!.Value.SetResult();
                _sources.RemoveFirst();
            }
        }
    }

    public void Release(int count)
    {
        lock (_lock)
        {
            _count += count;
            for (int i = Math.Min(_sources.Count, count); i > 0; i--)
            {
                _sources.First!.Value.SetResult();
                _sources.RemoveFirst();
            }
        }
    }

    public void Enter(int count)
    {
        lock (_lock)
            _count -= count;
    }

    public Task WaitAsync()
    {
        lock (_lock)
        {
            if (--_count >= 0)
                return Task.CompletedTask;
            else
            {
                TaskCompletionSource source = new();
                _sources.AddLast(source);
                return source.Task;
            }
        }
    }
}

Accord•2y ago

Looks like nothing has happened here. I will mark this as stale and this post will be archived until there is new activity. Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity. Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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Programming

❔ ❔ ❔ SemaphoreSlim that can be entered without waiting