task

task 可以通过CancellationTokenSource.token 来控制线程是否终止。

同时 还可以注册一个委托，来回调。

Register(Action)

Registers a delegate that will be called when this CancellationToken is canceled.

 

ThrowIfCancellationRequested

Throws a OperationCanceledException if this token has had cancellation requested.