C＃异步调用“调用并忘记”

Question

In c# when you invoke the await method inside an async method, the code will be executed from the calling context to that method. What if I want to make an asynchronous call which will just continue from the same line of code directly (even if the asynchronous action did not finish yet) instead of getting back to the calling context? How can I do that?

Answer 1

An await is, by definition, a point at which you must asynchronously wait for the task to finish before continuing the workflow. If you don't have to wait, then don't wait! There is no requirement that you await anything.

Your question is rather like asking "I have an IEnumerable<int> but I don't care what integers are in it; do I have to foreach over it?" No, you don't. If you don't care what the result is, you don't have to get a result from a sequence. If you don't care what the result of a task is, you don't have to await it.

But it is a strange thing to get a sequence and then not enumerate it, and it is a strange thing to get a task and then not care about what happens when it completes.

Answer 2

What if I want to make an asynchronous call which will just continue from the same line of code directly (even if the asynchronous action did not finish yet) instead of getting back to the calling context? How can I do that?

The easiest way, which works whether Something is synchronous or asynchronous:

var _ = Task.Run(() => Something());

But, as Eric Lippert stated:

it is a strange thing to get a task and then not care about what happens when it completes.

Or, as I like to put it: fire-and-forget is almost never what you really want. To "forget" means:

1. You don't care when it completes.
2. You don't care whether it completes. Eg, if your app exits (or app pool is recycled if on ASP.NET), then your background work is just lost.
3. You don't care whether it completes successfully . Eg, if your work throws an exception, you want to silently swallow that exception.

In real-world code, this scenario is extremely rare.

Answer 3

If you want to start the async method and continue inside the function you can do something like Task<string> getStringTask = asyncMethodThatReturnsString(); . Then continue until you want to wait for the async task to finish at which point you would call string output = await getStringTask; .