Futures: There should be a way to interrupt wgpuInstanceWaitAny via CPU-timeline event

[kainino0x]

Originally we did not have any way to interrupt running WaitAny calls, or generally send CPU→CPU events. The reason for this was that vkWaitForFences cannot do it. However, since we have a clean distinction between CPU-timeline and Queue-timeline operations, this is actually very simple to add (it's exactly how async pipeline creation works, already).

One important design pattern needs it, which is having an application thread which uses WaitAny to watch for events and e.g. forward them into an event loop. It needs to be possible to interrupt WaitAny each time a new Future is created, so the new Future can be added to its list. This is only possible with mixed-source waiting, but most systems should have that capability.

[kainino0x]

This is only possible with mixed-source waiting, but most systems should have that capability.

I misspoke. We don't currently allow mixed-source waiting at all. So part of this feature request is that we need mixed-source waiting as well.

[kainino0x]

This is only possible with mixed-source waiting, but most systems should have that capability.

I misspoke. We don't currently allow mixed-source waiting at all. So part of this feature request is that we need mixed-source waiting as well.

#506

[kainino0x]

Jan 23 meeting:

• LK: summary
• CF: Not possible in Vulkan… maybe Metal
• KN: Possible in Metal. Also possible in Vulkan with extensions, not sure how many devices.
• LK: Can use background threads to do vkWaitForFences and then forward the ...
• CF: Running our own runtime / reactor?
• KN: Not sure reactors usually have to deal with multiple incompatible sources
• CF: Have found D3D12 events can't be waited along with network events, unless there's a way to convert them that I didn't find
  • KN: Did some research on this, I think there was a way to turn network events into the handle type d3d12 uses
• LK: …
• CF: Can't bake the ability to interop into the API, sometimes we just can't do it
• LK: Other part of issue… app has to track a list of futures and then call WaitAny. But then when there is a new future in the list there's no way to interrupt WaitAny and add it to the list.
• CF: events guaranteed not to finish until after all the ones you're waiting for
  • LK/KN: Not required by JS spec
  • CF: Ah, mapping a buffer that was used earlier
• KN: Tied up in the fact we only have one queue. But is there something we can do with the fact that queues are ordered?
• LK: Users can make the map callback AllowSpontaneous

[kainino0x]

• KN: Did some research on this, I think there was a way to turn network events into the handle type d3d12 uses

I don't think this is what I was thinking of, but supposedly it might be possible with WSAWaitForMultipleEvents? https://stackoverflow.com/a/41749725 @cwfitzgerald

[kainino0x]

The thing I'm remembering probably had something to do with IOCP. Trying to find it I stumbled on a different interesting thing:

https://www.reddit.com/r/cpp/comments/1f1p0yd/comment/lk0jbtl/

Supposedly you can use IOCP to wait on events. I do not know if this works with D3D events.