I know that Task.Wait() block thread in which it is executed.
Do I understand correctly that Task.WaitAsync() does not do this?
I tried to find information about it but I didn't find anything
2 Answers
WaitAsync will return a new task that needs to be awaited in turn. It's not used to avoid await, it's used to allow cancelling a wait for another task.
If you want you await for a task to complete without blocking you'll have to use await in an async method, or use ContinueWith with the continuation code:
async Task MyMethodAsync(Task myTask) { ... await myTask; ... } This code can await forever and doesn't allow cancelling the wait. If you want to stop waiting after a while you can use Task.WaitAsync
... try { await myTask.WaitAsync(TimeSpan.FromMinute(1)); } catch(TimeoutException) { //Handle the timeout } ... Or you may want to cancel awaiting that task if a parent call signals cancellation through a CancellationTokenSource
async Task MyMethod(Task someTask,CancellationToken cancellationToken=default) { .... await someTask.WaitAsync(cancellationToken); ... } 
answered Aug 23, 2022 at 9:56
Panagiotis Kanavos
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It is non-blocking since it returns a Task. See the documentation.
public Task WaitAsync(CancellationToken cancellationToken); public Task WaitAsync(TimeSpan timeout); public Task WaitAsync(TimeSpan timeout, CancellationToken cancellationToken); Gets a
Taskthat will complete when thisTaskcompletes, when the specified timeout expires, or when the specifiedCancellationTokenhas cancellation requested.
The implementation can be found here:
public static Task WaitAsync(this Task task, int millisecondsTimeout) => WaitAsync(task, TimeSpan.FromMilliseconds(millisecondsTimeout), default); public static Task WaitAsync(this Task task, TimeSpan timeout) => WaitAsync(task, timeout, default); public static Task WaitAsync(this Task task, CancellationToken cancellationToken) => WaitAsync(task, Timeout.InfiniteTimeSpan, cancellationToken); public async static Task WaitAsync(this Task task, TimeSpan timeout, CancellationToken cancellationToken) { var tcs = new TaskCompletionSource<bool>(); using (new Timer(s => ((TaskCompletionSource<bool>)s).TrySetException(new TimeoutException()), tcs, timeout, Timeout.InfiniteTimeSpan)) using (cancellationToken.Register(s => ((TaskCompletionSource<bool>)s).TrySetCanceled(), tcs)) { await(await Task.WhenAny(task, tcs.Task).ConfigureAwait(false)).ConfigureAwait(false); } } 
Task.WaitAsync()is useful when you want to make aTaskcancellable based on a timeout and executes without blocking.