[REVIEW] Add cuda_event type

[achirkin]

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1. Add new cuda_event and cuda_event_view wrappers, similar to cuda_stream and cuda_stream_view.
2. Add extra functionality to cuda_stream and cuda_stream_view to interact with the added event types.

[achirkin]

A few days ago @jrhemstad mentioned you'd welcome this wrapper. I tried to follow cuda_stream approach as close as possible, so some copy-pasting is there.

[achirkin]

Thanks, @jrhemstad ! I wouldn't mind moving the wait and record, but then we need to make a choice: shall I add another event_view, or better just make duplicate methods for rmm::cuda_event and cudaEvent_t? And there is also wait without arguments, which synchronises with the host (cudaEventSynchronize), which I cannot move to stream_view.

On the other hand, I can just change the wording to something like... synchronize/wait_by and push/record_in?

[jrhemstad]

Yes, I think we will need an event_view type.

And there is also wait without arguments, which synchronises with the host (cudaEventSynchronize), which I cannot move to stream_view.

Good point. We should keep that as a wait function in the event type.

[achirkin]

There would also be some inconvenience in having to explicitly convert stream types to the stream_view to access its member functions if we move wait and record there, right? Still better than having them in cuda_event? :)

[jrhemstad]

We should design for a world where cudaStream_t isn't used directly anymore.

Eventually these types will all exist in libcu++.

[achirkin]

Done. Sorry I don't have the rights to set github labels here.

[achirkin]

Also note, I added a function that doesn't strictly belong to the PR (I hope it's ok). I need it in cuml to decide if I need one worker stream or two (if I cannot use the default). I thought it would be useful for others too: https://github.com/rapidsai/rmm/blob/b55088b3a1433b0248dddab319d10771cb8d97ba/include/rmm/cuda_stream_view.hpp#L96-L118

[harrism]

I think this still requires a bit of design work, and we are in burn down for 21.10 so I'm moving this to the next release. @achirkin please change the target branch.

[achirkin]

Ok, though I hoped to push it in 21.10, cause I need events in https://github.com/rapidsai/cuml/pull/4201 .

[harrism]

@achirkin you can use CUDA events now without a wrapper class. We already use events in RMM. I think we should take our time and get this right, and perhaps it should just live in libcu++ from the beginning.

[ajschmidt8]

Removing ops-codeowners from the required reviews since it doesn't seem there are any file changes that we're responsible for. Feel free to add us back if necessary.

[github-actions[bot]]

This PR has been labeled inactive-30d due to no recent activity in the past 30 days. Please close this PR if it is no longer required. Otherwise, please respond with a comment indicating any updates. This PR will be labeled inactive-90d if there is no activity in the next 60 days.

[github-actions[bot]]

This PR has been labeled inactive-90d due to no recent activity in the past 90 days. Please close this PR if it is no longer required. Otherwise, please respond with a comment indicating any updates.