Skip list priority implementation

[btovar]

This implementation has only one cursor. Let's see if it is enough as compared to work queue.

Merge Checklist

The following items must be completed before PRs can be merged.
Check these off to verify you have completed all steps.

• make test Run local tests prior to pushing.
• make format Format source code to comply with lint policies. Note that some lint errors can only be resolved manually (e.g., Python)
• make lint Run lint on source code prior to pushing.
• Manual Update: Update the manual to reflect user-visible changes.
• Type Labels: Select a github label for the type: bugfix, enhancement, etc.
• Product Labels: Select a github label for the product: TaskVine, Makeflow, etc.
• PR RTM: Mark your PR as ready to merge.

[JinZhou5042]

I’m wondering why it was necessary to mark a node as dead instead of deleting it directly. I know a regular list works this way, and I have no objection to it, just want to understand the rationale behind this.

[dthain]

Overall, this is looking good, and I like how you have simplified several taskvine issues while maintaining basically the same interface to the list. I have a couple of persnickety naming fixups, but no major concerns.

[btovar]

@dthain Sounds good!

@JinZhou5042 It is so that we can have more than one cursor pointing to the same node. We do not want to delete a node to which a cursor is pointing to as that will cause a segfault. Additionally, this allows us to 'delete' the item a cursor is pointing to during an iteration, which simplifies the places where we have to call 'next'.

[JinZhou5042]

@btovar Got it! I think this is a nice and very maintanable implementation, especially the design in send_one_task that allows us to retrieve ready tasks while evaluating their eligibility. It also makes it simple to expire tasks with missing inputs in the future PR.

[btovar]

any concerns if I merge this pr? I have been running VineReduce+cortado on top it successfully.

[dthain]

I think if you can run Cortado successfully with a clean valgrind, then I am comfortable merging.