问题
I have the following code:
public async Task SendPushNotificationAsync(string username, string message)
{
var task = ApnsNotifications.Instance.Hub.SendAppleNativeNotificationAsync(alert, username);
if (await Task.WhenAny(task, Task.Delay(500)) == task) {
return true;
}
return false;
}
I noticed that SendAppleNativeNotificationAsync was hanging indefinitely (never returning out of the containing method), so I tried telling it to cancel after 500ms. But still... the call to WhenAny now hangs and I never see a return get hit, resulting in the consumer just waiting indefinitely (it's a sync method calling this async method, so I call .Wait()):
_commService.SendPushNotificationAsync(user.Username, notificationDto.PushContent).Wait(TimeSpan.FromSeconds(1));
How do I force this to finish after a set time, no matter what?
What happens if I simply "fire and forget", instead of awaiting the Task?
回答1:
it's a sync method calling this async method, so I call .Wait()
And that's your problem. You're deadlocking because you're blocking on asynchronous code.
The best solution for this is to use await instead of Wait:
await _commService.SendPushNotificationAsync(user.Username, notificationDto.PushContent);
If you absolutely can't use await, then you can try one of the hacks described in my Brownfield Async article.
来源：https://stackoverflow.com/questions/40363918/async-task-hanging