November 2020
Intermediate to advanced
226 pages
5h 34m
Chinese
Content preview from C#并发编程经典实例（第2版）
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166
｜
第
12
章
再次，应该尽可能地把锁中的代码最小化。另外，需要注意阻塞调用，在理想状态下，当
锁定时，应该避免阻塞代码。
最后，避免在锁定状态下调用任意代码，包括触发事件、调用虚拟方法以及调用委托。如
果必须调用代码，那么可以在锁解除后再调用。
参阅
12.2
节探讨兼容
async
的锁，
lock
语句和
await
并不兼容。
12.3
节探讨线程间通信。
lock
语句用于保护共享数据，而不是在线程之间传递信号。
12.5
节探讨节流，这是对锁的一种泛化。锁可以当作一次一发的节流。
12.2
异步锁
问题
假设有一些共享数据，需要从多个代码块安全地读取和写入，而这些代码块可能使用了
await
。
解决方案
.NET
框架的
SemaphoreSlim
类型在
.NET 4.5
中完成了更新，可以兼容
async
，下面是使用
示例：
class
MyClass
{
// 该锁保护_value域
private readonly
SemaphoreSlim _mutex =
new
SemaphoreSlim(1);
private int
_value;
public async
Task DelayAndIncrementAsync()
{
await
_mutex.WaitAsync();
try
{
int
oldValue = _value;
await
Task.Delay(TimeSpan.FromSeconds(oldValue));
_value = oldValue + 1;
} ...
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