AsyncLazy<T>.SuppressRelevance 方法

定義

命名空間:

Microsoft.VisualStudio.Threading

組件:

Microsoft.VisualStudio.Threading.dll

套件:

Microsoft.VisualStudio.Threading v17.11.20

將後面的程式代碼標示為與接收 AsyncLazy<T> 值處理站無關。

public Microsoft.VisualStudio.Threading.AsyncLazy<T>.RevertRelevance SuppressRelevance ();

member this.SuppressRelevance : unit -> Microsoft.VisualStudio.Threading.AsyncLazy<'T>.RevertRelevance

Public Function SuppressRelevance () As AsyncLazy(Of T).RevertRelevance

傳回

AsyncLazy<T>.RevertRelevance

要處置的值，以將相關性還原至實值處理站。

備註

在某些情況下，異步工作可能會在實值處理站內關閉。 當值處理站 不需要 在值處理站完成之前完成此工作時，使用此方法將該程式代碼標示為與值處理站無關會很有用。 特別是，當 Spun off 工作可能實際包含程式代碼，而程式代碼可能會等候值處理站本身完成時，就可能是必要的。 如果值處理站尚未完成，則這類情況 InvalidOperationException 會導致擲 GetValueAsync(CancellationToken) 回 ，這可能會在程式中造成不具決定性的失敗。

using程式代碼周圍的區塊可協助程序達到可靠的行為，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>如果使用 建立JoinableTaskFactory，這個方法也會在該處理站相關聯的 上Context呼叫 SuppressRelevance() 。