Task的TaskCompletionSource

Question

如何为Task而不是Task<TResult>创建TaskCompletionSource ？

Answer 1

There is no non-generic version. However, Task<T> derives from Task , so you can just use TaskCompletionSource<bool> and return the task.

Task SomeMethodAsync()
{
    var tcs = new TaskCompletionSource<bool>();

    // Implement method as needed

    return tcs.Task; // Return the Task<bool> as a Task
}

Note that I'm using bool just because it's a small value type, and the result will get "thrown away". Another option here is to make your own custom type and return that, ie:

private struct EmptyType {}

Task SomeMethodAsync()
{
    var tcs = new TaskCompletionSource<EmptyType>();

    // Implement method as needed
    // Use tcs.SetResult(default(EmptyType)) or similar

    return tcs.Task; // Return the Task<bool> as a Task
}

The main advantage here is the type is the smallest possible (least waste), and a type that doesn't suggest there is a "value" contained within the result (if the consumer does use reflection, etc).