修复了全局节点连接异常异常。

Library/Utils/LinqHelper.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Serein.Library.Utils
+{
+    /// <summary>
+    /// 对于 linq 的异步扩展方法
+    /// </summary>
+    public static class LinqHelper
+    {
+        /// <summary>
+        /// 根据条件筛选，只保留第一个满足条件的元素，其余的不包含。
+        /// </summary>
+        public static IEnumerable<T> DistinctByCondition<T>(
+            this IEnumerable<T> source,
+            Func<T, bool> predicate)
+        {
+            var seenKeys = new HashSet<T>();
+
+            foreach (var item in source)
+            {
+                if (!predicate(item))
+                    continue;
+
+                /*var key = keySelector(item);
+                if (seenKeys.Add(key)) // 如果是新键*/
+                yield return item;
+            }
+        }
+
+        public static async Task<IEnumerable<TResult>> SelectAsync<TSource, TResult>(this IEnumerable<TSource> source,
+                                                                                          Func<TSource, Task<TResult>> method)
+        {
+            return await Task.WhenAll(source.Select(async s => await method(s)));
+        }
+
+
+        public static async Task<IEnumerable<TResult>> SelectAsync<TSource, TResult>(this IEnumerable<TSource> source, 
+                                                                                          Func<TSource, Task<TResult>> method,
+                                                                                          int concurrency = int.MaxValue)
+        {
+            var semaphore = new SemaphoreSlim(concurrency);
+            try
+            {
+                return await Task.WhenAll(source.Select(async s =>
+                {
+                    try
+                    {
+                        await semaphore.WaitAsync();
+                        return await method(s);
+                    }
+                    finally
+                    {
+                        semaphore.Release();
+                    }
+                }));
+            }
+            finally
+            {
+                semaphore.Dispose();
+            }
+        }
+    }
+}