Enhance blocksmith selection

[nawikart]

Description

Currently blocksmith is selected by sorting the node registry and assign index of smithing based on their order.

We'll update that behavior to use random number generator to pick an index of sorted node registry (sorted by nodeID so we sort rarely) by using previousBlock.BlockSeed as the seed. With this we open the possibility to let first and second blocksmith be the same node, so we need to handle this carefully given the implementation on mempool and block generate wait time.

note: start tracing this function on BlockService:WillSmith() function.

Breakdown

• create a candidate struct

Candidate struct {
    Blocksmith Blocksmith
    StartTime int64
    ExpiryTime int64
}

• WillSmith function will be removed from BlockService
• Refactor BlocksmithStrategy

type BlocksmithStrategyInterface interface {
    WillSmith(previousBlock *model.Block) bool
    IsSmithingTimeValid(block *model.Block) bool
}

type BlocksmithStrategy struct {
    candidates []Candidate
    lastPreviousBlockHash [32]byte // 
}

• BlocksmithStrategy.WilSmith should checks if current_time is good for current_node to smith

• BlocksmithStrategy.IsSmithingTimeValid, should checks if provided Block contain a correct BlocksmithPublicKey and BlockTimestamp regardless the node's current time.

• generate random number for blocksmith index (still waiting for decision which to choose), by providing:

  • previousBlock.BlockSeed + constant("blocksmith-selection") - as random seed
  • sorted node registry from Enhance: Cache NodeRegistries #1189

• modify skipped blocksmith mechanism to allow 1 blocksmith to skip twice.

• modify block creation code to handle in case single node selected as blocksmith twice in a row.

• PushBlock with skipped blocksmith should be faster now, as it won't proccess: admit/expel nodes, participation score calculation, skipped blocksmith calculation before accepted block is marked as persistable

[iltoga]

lgtm

[andy-shi88]

move back to WIP
unhandled case:

when previousBlock has few skipped blocksmith, the next blocksmith time has not been normalized to start from previousBlock persist time, causing propagated skipped blocksmith for a few first block after skipped blocksmith, and could cause huge smithing time shifting when some nodes are not online for long time.