使用Nito.AsyncEx实现异步锁

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：

 public class AsyncLockDemo
     {
         //private readonly object _mutex = new object();
         private readonly AsyncLock _mutex = new AsyncLock();
         private int i = ;
         public void Execute()
         {
             Console.WriteLine("before call foo1: "+ i);

             Foo1().ContinueWith(new Action<Task>(t =>
             {
                 Console.WriteLine("foo1 completed: " + i);
             }));

             Console.WriteLine("after call foo1: " + i);

             Console.WriteLine("before call foo2: " + i);

             Foo2().ContinueWith(new Action<Task>(t =>
             {
                 Console.WriteLine("foo2 completed: " + i);
             }));

             Console.WriteLine("after call foo2: " + i);
         }

         public async Task Foo1()
         {
             using (await _mutex.LockAsync())
             {
                 await Task.Delay(TimeSpan.FromSeconds());
                 Console.WriteLine("Foo1 start: " + i);
                 await DoSomethingAsync();
                 Console.WriteLine("Foo1 end: " + i);
             }
         }

         public async Task Foo2()
         {
             using (await _mutex.LockAsync())
             {
                 Console.WriteLine("Foo2 start: " + i);
                 //await Task.Delay(TimeSpan.FromSeconds(1));
                 await DoSomethingAsync();
                 Console.WriteLine("Foo2 end: " + i);
             }
         }

         private Task DoSomethingAsync(int j)
         {
             return Task<string>.Run(() =>
             {
                 Thread.Sleep();
                 i = j;
             });
         }
     }

运行结果如下：