[POC] Move SocketAsyncEngine to System.Threading so different SafeHandle types can use it.

src/libraries/Common/src/Interop/Unix/System.Native/Interop.HandleEvents.cs

@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.InteropServices;
+
+internal static partial class Interop
+{
+    internal static partial class Sys
+    {
+        [Flags]
+        internal enum HandleEvents : int
+        {
+            None = 0x00,
+            Read = 0x01,
+            Write = 0x02,
+            ReadClose = 0x04,
+            Close = 0x08,
+            Error = 0x10
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        internal struct HandleEvent
+        {
+            public IntPtr Data;
+            public HandleEvents Events;
+            private int _padding;
+        }
+
+        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_CreateHandleEventPort")]
+        internal static unsafe partial Error CreateHandleEventPort(IntPtr* port);
+
+        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_CloseHandleEventPort")]
+        internal static partial Error CloseHandleEventPort(IntPtr port);
+
+        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_CreateHandleEventBuffer")]
+        internal static unsafe partial Error CreateHandleEventBuffer(int count, HandleEvent** buffer);
+
+        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_FreeHandleEventBuffer")]
+        internal static unsafe partial Error FreeHandleEventBuffer(HandleEvent* buffer);
+
+        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_TryChangeHandleEventRegistration")]
+        internal static partial Error TryChangeHandleEventRegistration(IntPtr port, SafeHandle socket, HandleEvents currentEvents, HandleEvents newEvents, IntPtr data);
+
+        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_TryChangeHandleEventRegistration")]
+        internal static partial Error TryChangeHandleEventRegistration(IntPtr port, IntPtr socket, HandleEvents currentEvents, HandleEvents newEvents, IntPtr data);
+
+        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_WaitForHandleEvents")]
+        internal static unsafe partial Error WaitForHandleEvents(IntPtr port, HandleEvent* buffer, int* count);
+    }
+}

src/libraries/Common/src/Interop/Wasi/System.Native/Interop.SocketEvent.cs → src/libraries/Common/src/Interop/Wasi/System.Native/Interop.HandleEvents.cs

@@ -9,7 +9,7 @@ internal static partial class Interop
     internal static partial class Sys
     {
         [Flags]
-        internal enum SocketEvents : int
+        internal enum HandleEvents : int
         {
             None = 0x00,
             Read = 0x01,