AsyncLazy<T>.SuppressRelevance 方法
定义
重要
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将后面的代码标记为与接收 AsyncLazy<T> 值工厂无关。
public Microsoft.VisualStudio.Threading.AsyncLazy<T>.RevertRelevance SuppressRelevance ();member this.SuppressRelevance : unit -> Microsoft.VisualStudio.Threading.AsyncLazy<'T>.RevertRelevancePublic Function SuppressRelevance () As AsyncLazy(Of T).RevertRelevance返回
要释放的值，以将相关性还原到值工厂。
注解
在某些情况下，异步工作可能会在值工厂内展开。 如果值工厂 不需要 在值工厂完成之前完成此工作，则使用此方法将代码标记为与值工厂无关会很有用。 具体而言，当抛出任务实际上可能包含可能本身等待值工厂本身完成的代码时，可能需要这样做。 如果值工厂尚未完成，则这种情况将导致 InvalidOperationException 引发 GetValueAsync(CancellationToken) ，这可能会在程序中引入不确定的故障。
using抛出代码周围的块可帮助程序实现可靠的行为，如下所示。
class MyClass {
private readonly AsyncLazy<int> numberOfApples;
public MyClass() {
this.numberOfApples = new AsyncLazy<int>(async delegate {
// We have some fire-and-forget code to run.
// This is *not* relevant to the value factory, which is allowed to complete without waiting for this code to finish.
using (this.numberOfApples.SuppressRelevance()) {
this.FireOffNotificationsAsync();
}
// This code is relevant to the value factory, and must complete before the value factory can complete.
return await this.CountNumberOfApplesAsync();
});
}
public event EventHandler? ApplesCountingHasBegun;
public async Task<int> GetApplesCountAsync(CancellationToken cancellationToken) {
return await this.numberOfApples.GetValueAsync(cancellationToken);
}
private async Task<int> CountNumberOfApplesAsync() {
await Task.Delay(1000);
return 5;
}
private async Task FireOffNotificationsAsync() {
// This may call to 3rd party code, which may happen to call back into GetApplesCountAsync (and thus into our AsyncLazy instance),
// but such calls should *not* be interpreted as value factory reentrancy. They should just wait for the value factory to finish.
// We accomplish this by suppressing relevance of the value factory while this code runs (see the caller of this method above).
this.ApplesCountingHasBegun?.Invoke(this, EventArgs.Empty);
}
}
AsyncLazy<T>如果 是使用 JoinableTaskFactory创建的，则此方法还会在与该工厂关联的 上Context调用 SuppressRelevance() 。