Is there any way to cancel multiple tasks at once?

Ray Core
1

Hi, Is there any way to cancel multiple object reference at once? Here is the definition of ray.cancel:
def cancel(object_ref: "ray.ObjectRef", *, force: bool = False, recursive: bool = True):
So I cannot do this:

readies, rests = ray.wait(futures, timeout=10, num_returns=1)
ray.cancel(*rests)

I get an error:
TypeError: cancel() takes 1 positional argument but 4 were given

2

Hi @kyleqian ! Currently ray.cancel takes only a single object ref. I think improving it to take a list of object refs is not a bad idea (feature request is here [Core] `ray.cancel` multiple ObjectRefs · Issue #24559 · ray-project/ray · GitHub).

What kind of workload are you running? Would batching cancel requests speed it up in some way?

3

Thank you. I use Ray to process images and often need to cancel multiple tasks if one of them failed. Batching cancel requests could be have better performance than manual loop.

4

I see. How big of a performance improvement would you have if you had the ability to cancel in batch? If it’s large then we can add that to the GitHub issue for prioritization :slight_smile:

5

When some tasks fail, dozens to hundreds of related tasks may be canceled. I think batching cancel request can reduce the number of RPCs, and it will make the code more concise.

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