Add AsyncLock (#44)

src/SkyWalking.Core/Remote/GrpcConnectionManager.cs

@@ -17,14 +17,11 @@
  */
 
 using System;
-using System.Collections.Generic;
 using System.Linq;
-using System.Runtime.CompilerServices;
-using System.Threading;
 using System.Threading.Tasks;
-using Nito.AsyncEx;
 using SkyWalking.Config;
 using SkyWalking.Logging;
+using SkyWalking.Utils;
 
 namespace SkyWalking.Remote
 {

src/SkyWalking.Core/SkyWalking.Core.csproj

@@ -17,7 +17,6 @@
     <ProjectReference Include="..\SkyWalking.NetworkProtocol\SkyWalking.NetworkProtocol.csproj" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="Nito.AsyncEx.Coordination" Version="5.0.0-pre-05" />
     <PackageReference Include="System.Diagnostics.DiagnosticSource" Version="4.4.1" />
   </ItemGroup>
 </Project>
\ No newline at end of file

src/SkyWalking.Core/Utils/AsyncLock.cs

+/*
+ * Licensed to the OpenSkywalking under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace SkyWalking.Utils
+{
+    internal class AsyncLock
+    {
+        private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(1);
+        private readonly Releaser _releaser;
+        private readonly Task<Releaser> _releaserTask;
+
+        public AsyncLock()
+        {
+            _releaser = new Releaser(this);
+            _releaserTask = Task.FromResult(_releaser);
+        }
+
+        public Task<Releaser> LockAsync(CancellationToken cancellationToken = default(CancellationToken))
+        {
+            var wait = _semaphore.WaitAsync(cancellationToken);
+
+            return wait.IsCompleted
+                ? _releaserTask
+                : wait.ContinueWith(
+                    (_, state) => ((AsyncLock) state)._releaser,
+                    this, CancellationToken.None,
+                    TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
+        }
+
+        public Releaser Lock()
+        {
+            _semaphore.Wait();
+
+            return _releaser;
+        }
+
+        public struct Releaser : IDisposable
+        {
+            private readonly AsyncLock _toRelease;
+
+            internal Releaser(AsyncLock toRelease)
+            {
+                _toRelease = toRelease;
+            }
+
+            public void Dispose()
+                => _toRelease._semaphore.Release();
+        }
+    }
+}
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