LibUv Networking (#65)

Projects/Server/LibUv/LibuvAwaitable.cs

@@ -0,0 +1,79 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using Libuv.Internal;
+
+namespace Libuv
+{
+  public class LibuvAwaitable<TRequest> : ICriticalNotifyCompletion where TRequest : UvRequest
+  {
+    private static readonly Action _callbackCompleted = () => { };
+
+    private Action _callback;
+
+    private UvException _exception;
+
+    private int _status;
+
+    public static readonly Action<TRequest, int, UvException, object> Callback = (req, status, error, state) =>
+    {
+      var awaitable = (LibuvAwaitable<TRequest>)state;
+
+      awaitable._exception = error;
+      awaitable._status = status;
+
+      var continuation = Interlocked.Exchange(ref awaitable._callback, _callbackCompleted);
+
+      continuation?.Invoke();
+    };
+
+    public LibuvAwaitable<TRequest> GetAwaiter() => this;
+    public bool IsCompleted => ReferenceEquals(_callback, _callbackCompleted);
+
+    public UvWriteResult GetResult()
+    {
+      Debug.Assert(_callback == _callbackCompleted);
+
+      var exception = _exception;
+      var status = _status;
+
+      // Reset the awaitable state
+      _exception = null;
+      _status = 0;
+      _callback = null;
+
+      return new UvWriteResult(status, exception);
+    }
+
+    public void OnCompleted(Action continuation)
+    {
+      // There should never be a race between IsCompleted and OnCompleted since both operations
+      // should always be on the libuv thread
+      if (ReferenceEquals(_callback, _callbackCompleted))
+        Debug.Fail($"{typeof(LibuvAwaitable<TRequest>)}.{nameof(OnCompleted)} raced with {nameof(IsCompleted)}, scheduling callback.");
+
+      _callback = continuation;
+    }
+
+    public void UnsafeOnCompleted(Action continuation)
+    {
+      OnCompleted(continuation);
+    }
+  }
+
+  public struct UvWriteResult
+  {
+    public int Status { get; }
+    public UvException Error { get; }
+
+    public UvWriteResult(int status, UvException error)
+    {
+      Status = status;
+      Error = error;
+    }
+  }
+}