如何保证异步方法继续在另一个线程上运行？

Question

Does ConfigureAwait(false) guarantee that continuation runs on a different thread or only signals that it's not compulsory to run on the same thread?

Is there any way to provide that guarantee?

I need to test context flow across threads.

Answer 1

Using ConfigureAwait(false) tells the awaiter not to resume on the captured context and so the SynchronizationContext is ignored. That means that the continuation would be scheduled by the default TaskScheduler that uses ThreadPool threads.

If the original thread was a ThreadPool thread, the continuation may run on the same thread, otherwise your guaranteed it's a different thread.

You can start your test using a dedicated thread without a SynchronizationContext (or with ConfigureAwait(false) ) to make sure the threads are different before and after the async operation.

Answer 2

There's below scenario which ConfigureAwait(false) doesn't run a new context.

Task task2Seconds = Wait2Seconds();
Task task5Seconds = Wait5Seconds();

await task5Seconds;
await task2Seconds.ConfigureAwait(false);

The first await doesn't have that ConfigureAwait(false) but it takes longer than the second await who has that configure but be ready to resume in advance. So the second will resume on the same context.