4

I'm creating a system which will spawn a lot of worker tasks and in some point of my app I'm doing a Task.WaitAny to retrieve the first finished task.

My concern is about how many tasks can I send to WaitAny, I know WaitHandle's WaitAny/All only can support up to 64 wait handles and I'm not sure if the underlying mechanism on Task.WaitAny uses internally wait handles to wait for a finished task and thus these limits apply to them.

Is there any limit to how many tasks can be passed to Task.WaitAny like with WaitHandles or there's no limit?

Cheers.

Improve this question
9
  • Perhaps you should consider using TPL action blocks (stackoverflow.com/a/37975762/982639) for this purpose, and a manual reset event (msdn.microsoft.com/en-us/library/…) / auto-reset events (msdn.microsoft.com/en-us/library/…) Commented Sep 6, 2016 at 17:10
  • I don't see how this can help or benefit on my situation (I know I gave very little info of my project), also, I don't want to add a library (which I don't even know if it's supported by .net Core which my project targets) if I can just use the framework itself. Commented Sep 6, 2016 at 17:14
  • That's the problem essentially, its hard for me to give you a good answer with little information, but I have to say that if you have to add async to the mix one day, you should consider using TPL...that's just from my experience though. In any case, you won't need to worry about limits with action blocks...and if you thread the code properly you will be able to wait for all action blocks to complete, which makes your problem go away... Commented Sep 6, 2016 at 17:24
  • Hmmm, Task.WaitAny already uses async, all my code is really async... And I don't want to wait all actions to continue (that's stated on my question), I want to get the first one in finish, My code is a task queue, whenever a task finishes it must take some actions, so I can't wait for all to finish or the purpose of this queue will be defeated. Commented Sep 6, 2016 at 17:28
  • Right, so - my idea was, in the logic block where you do your task action, in the code right after it completes the action or logic, you just add some more code to take some action as you put it, does that not suffice? If you wanted to cancel all blocks here you could do that too, with a cancellation token... Commented Sep 6, 2016 at 17:41

2 Answers 2

Reset to default
5

From what I see, it internally works by chaining a continuation to all the tasks: http://referencesource.microsoft.com/#mscorlib/system/threading/Tasks/TaskFactory.cs,db51a91904616672
(with internal optimizations, as well as some code to handle the racing condition when multiple tasks end at once)

Therefore, the limitations on WaitHandles shouldn't apply here.

Improve this answer
Sign up to request clarification or add additional context in comments.

1 Comment

Perfect, that's what I needed to know. Thanks!
4

Internally Task.WaitAny is calling TaskFactory.CommonCWAnyLogic which is scheduling a continuation on each task you pass in, that continuation marks which index in the array it was and allows the task to complete. It uses the inernal class CompleteOnInvokePromise which could be thought of as kind of a specialized TaskCompletionSource.

Because it is using task continuations and not wait handles the wait handle limit should not apply.

Improve this answer

Comments

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.