转载地址：http://www.cnblogs.com/1zhk/p/5269279.html
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<Task>(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<Task>(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<string>.Run(() =>
52 {
53 Thread.Sleep(2000);
54 i = j;
55 });
56 }
57 }
运行结果如下：
