事件触发时完成任务

Question

这应该很简单，但我只是无法将其聚焦。

在这个方法中

public static async Task<string> UnloadAsync(Assembly assy, bool silentFail = false)
{
  if (AssyLoadContext.__alcd.ContainsKey(assy))
  {
    var assemblyName = __namd.Where(kvp => kvp.Value == assy).First().Key;
    __alcd[assy].Unloading += alc => //signal the task to complete and return assemblyName
    __namd.Remove(assemblyName);
    __alcd[assy].Unload();
    __alcd.Remove(assy);
    Debug.WriteLine($"Unloaded assembly '{assy.GetName().Name}'");
  }
  if (silentFail) 
  {
    return null;
  }
  else
  {
    throw new InvalidOperationException($"Assembly '{assy.GetName().Name}' cannot be unloaded. Did you load it using AssyLoadContext.LoadWithPrivateContext(string assyPath)?");
  }
}

该AssemblyLoadContext.Unload()操作实际上是异步的，但不可等待。一旦不再有强 GC 引用等操作完成，程序集将卸载并触发 Unloading 事件。

返回值是assemblyName我想提供给延续的。

我可以找到所有关于需求的废话，await因为这就是产量发生的地方，但我不能那样写。你如何做到这一点没有await？

Answer 1

您正在寻找一个TaskCompletionSource<string>：

public static Task<string> UnloadAsync(Assembly assy, bool silentFail = false)
{
  if (AssyLoadContext.__alcd.ContainsKey(assy))
  {
    var tcs = new TaskCompletionSource<string>();
    var assemblyName = __namd.Where(kvp => kvp.Value == assy).First().Key;
    __alcd[assy].Unloading += alc => tcs.SetResult(assemblyName);
    __namd.Remove(assemblyName);
    __alcd[assy].Unload();
    __alcd.Remove(assy);
    Debug.WriteLine($"Unloaded assembly '{assy.GetName().Name}'");
    return tcs.Task;
  }
  if (silentFail)
  {
    return Task.FromResult<string>(null);
  }

  throw new InvalidOperationException($"Assembly '{assy.GetName().Name}' cannot be unloaded. Did you load it using AssyLoadContext.LoadWithPrivateContext(string assyPath)?");
  }
}

请注意，如果这抛出InvalidOperationException，它会在UnloadAsync被调用时抛出，而不是被包装在返回的Task（如果你的方法是async），就会发生这种情况。如果你想改变这一点，你可以使用 TaskCompletionSource：

public static Task<string> UnloadAsync(Assembly assy, bool silentFail = false)
{
  var tcs = new TaskCompletionSource<string>();
  if (AssyLoadContext.__alcd.ContainsKey(assy))
  {
    var assemblyName = __namd.Where(kvp => kvp.Value == assy).First().Key;
    __alcd[assy].Unloading += alc => tcs.SetResult(assemblyName);
    __namd.Remove(assemblyName);
    __alcd[assy].Unload();
    __alcd.Remove(assy);
    Debug.WriteLine($"Unloaded assembly '{assy.GetName().Name}'");
  }
  else if (silentFail)
  {
    tcs.SetResult(null);
  }
  else
  {
    tcs.SetException(throw new InvalidOperationException($"Assembly '{assy.GetName().Name}' cannot be unloaded. Did you load it using AssyLoadContext.LoadWithPrivateContext(string assyPath)?"));
  }
  
  return tcs.Task;
}

或者使用一种async方法：

public static async Task<string> UnloadAsync(Assembly assy, bool silentFail = false)
{
  if (AssyLoadContext.__alcd.ContainsKey(assy))
  {
    var tcs = new TaskCompletionSource<string>();
    var assemblyName = __namd.Where(kvp => kvp.Value == assy).First().Key;
    __alcd[assy].Unloading += alc => tcs.SetResult(assemblyName);
    __namd.Remove(assemblyName);
    __alcd[assy].Unload();
    __alcd.Remove(assy);
    Debug.WriteLine($"Unloaded assembly '{assy.GetName().Name}'");
    return await tcs.Task;
  }
  if (silentFail)
  {
    return null;
  }

  throw new InvalidOperationException($"Assembly '{assy.GetName().Name}' cannot be unloaded. Did you load it using AssyLoadContext.LoadWithPrivateContext(string assyPath)?");
}