Lock是常用的同步锁，但是我们无法在Lock的内部实现异步调用，比如我们无法使用await.

以下面的代码为例，当你在lock内部使用await时，VS会报错提醒。

最简单的解决办法就是使用第三方的库Nito.AsyncEx。可以通过Nuget安装。

通过AsyncLock就可以在锁的内部实现异步操作了。

样例代码如下：

1 public class AsyncLockDemo 2     { 3         //private readonly object _mutex = new object(); 4         private readonly AsyncLock _mutex = new AsyncLock(); 5         private int i = 0; 6         public void Execute() 7         { 8             Console.WriteLine("before call foo1: "+ i); 9 10             Foo1().ContinueWith(new Action
     
      (t =>11             {12                 Console.WriteLine("foo1 completed: " + i);13             }));14 15             Console.WriteLine("after call foo1: " + i);16 17             Console.WriteLine("before call foo2: " + i);18 19             Foo2().ContinueWith(new Action
      
       (t =>20             {21                 Console.WriteLine("foo2 completed: " + i);22             }));23 24             Console.WriteLine("after call foo2: " + i);25         }26 27         public async Task Foo1()28         {29             using (await _mutex.LockAsync())30             {31                 await Task.Delay(TimeSpan.FromSeconds(1));32                 Console.WriteLine("Foo1 start: " + i);33                 await DoSomethingAsync(1);34                 Console.WriteLine("Foo1 end: " + i);35             }36         }37 38         public async Task Foo2()39         {40             using (await _mutex.LockAsync())41             {42                 Console.WriteLine("Foo2 start: " + i);43                 //await Task.Delay(TimeSpan.FromSeconds(1));44                 await DoSomethingAsync(2);45                 Console.WriteLine("Foo2 end: " + i);46             }47         }48 49         private Task DoSomethingAsync(int j)50         {51             return Task
       
        .Run(() =>52             {53                 Thread.Sleep(2000);54                 i = j;55             });56         }57     }
       
      
     

运行结果如下：