Merge pull request #19 from dotnet-campus/t/lindexi/FerbeecelferrelawCeefeljalwedem

修复线程安全

Author: walterlv

AsyncWorkerCollection/ExecuteOnceAwaiter.cs

@@ -4,54 +4,58 @@
 
 namespace dotnetCampus.Threading
 {
+    /// <summary>
+    /// 只执行一次的等待
+    /// </summary>
+    /// <typeparam name="TResult"></typeparam>
     public class ExecuteOnceAwaiter<TResult>
     {
+        /// <summary>
+        /// 创建只执行一次的等待，调用 <see cref="ExecuteAsync"/> 时，无论调用多少次，只会执行 <paramref name="asyncAction"/> 一次
+        /// <para></para>
+        /// 因为此类使用了锁，因此需要调用方处理 <paramref name="asyncAction"/> 自身线程安全问题
+        /// </summary>
+        /// <param name="asyncAction">执行的具体逻辑，需要调用方处理自身线程安全问题</param>
         public ExecuteOnceAwaiter(Func<Task<TResult>> asyncAction)
         {
             _asyncAction = asyncAction;
         }
 
+        /// <summary>
+        /// 执行传入的具体逻辑，无论多少线程多少次调用，传入的具体逻辑只会执行一次
+        /// </summary>
+        /// <returns></returns>
         public Task<TResult> ExecuteAsync()
         {
-            if (_executionResult != null)
+            lock (_locker)
             {
+                if (_executionResult != null)
+                {
+                    return _executionResult;
+                }
+
+                _executionResult = _asyncAction();
                 return _executionResult;
             }
-
-            Lock(() => _executionResult = _asyncAction());
-
-            return _executionResult;
         }
 
+        /// <summary>
+        /// 在传入的具体逻辑执行完成之后，设置允许重新执行。如果此具体逻辑还在执行中，那么此方法调用无效
+        /// </summary>
         public void ResetWhileCompleted()
         {
-            if (IsCompleted)
+            lock (_locker)
             {
-                Lock(() => _executionResult = null);
+                if (_executionResult?.IsCompleted is true)
+                {
+                    _executionResult = null;
+                }
             }
         }
 
+        private readonly object _locker = new object();
+
         private readonly Func<Task<TResult>> _asyncAction;
         private Task<TResult> _executionResult;
-        private SpinLock _spinLock = new SpinLock(true);
-
-        private bool IsRunning => _executionResult?.IsCompleted is false;
-
-        private bool IsCompleted => _executionResult?.IsCompleted is true;
-
-        private void Lock(Action action)
-        {
-            var lockTaken = false;
-            try
-            {
-                _spinLock.Enter(ref lockTaken);
-                action();
-            }
-            finally
-            {
-                // 参数错误或锁递归时才会发生异常，所以此处几乎能肯定 lockTaken 为 true。
-                if (lockTaken) _spinLock.Exit();
-            }
-        }
     }
 }