在事件触发时完成任务

Question

这应该是简单的，但我就是不能使它成为焦点。

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)?");
}
}

AssemblyLoadContext.Unload()操作实际上是异步的，但不是可等待的。一旦没有强GC引用等，操作完成，程序集卸载并触发unload事件。

返回值是我想提供给continuation的assemblyName。

我能找到的所有文档都是关于需要await的，因为这是产量发生的地方，但我不能那样写。如果没有await，您如何做到这一点?

Answer 1

您正在寻找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)?");
}
}

注意，如果这抛出一个InvalidOperationException，它会在UnloadAsync被调用时被抛出，而不是被包装在返回的Task中(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($"Unloaded assembly '{assy.GetName().Name}'");
}
else if (silentFail)
{
tcs.SetResult(null);
}
else
{
tcs.SetException(new InvalidOperationException($"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)?");
}