[Optimize] Skip the scheduled batch proposal if already proposing

[ljedrz]

If I'm not missing anything, a batch proposal can be triggered by a timed loop or round progression, and if we're already proposing a batch for a new round, it seems reasonable to me that we may skip the timed one. This would save some network traffic and CPU use for the validators.

I tested it locally and can see the skip happening from time to time, which means those attempts can currently overlap.

[vvp]

Perhaps add some debug! message here for observing that there's an ongoing batch proposal attempt?

[ljedrz]

It could be useful, but if my intuition is correct, such an occurrence could just be ignored (so a log would only increase verbosity); either way works for me.

[howardwu]

Resolved in 44f498b

[raychu86]

The propose_batch call a few lines after this new skip already has a propose_lock. So having this check will only ensure that we can continue with this loop (and perform extra self_.sync.is_synced() checks) instead of awaiting on the propose_batch call.

I believe this change is safe, but don't see that much of a difference in terms of resource optimizations. Let me know if I'm missing anything.

[ljedrz]

@raychu86 you're right, it's nothing extreme, but it can avoid a duplicate proposal to be produced right after we produced one, which reduces CPU use and network traffic.