Added 2/3/4 cycle finalization options
Suppose B1, B2, B3, B4 are consecutive blocks and we are now processing the end of the cycle containing B4. * If B4 is justified using source B3, then B3 is finalized. * If B4 is justified using source B2, and B3 has been justified, then B2 is finalized. * If B3 is justified using source B1, and B1 has been justified, then B1 is finalized.
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vbuterin
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@ -217,8 +217,11 @@ The `BeaconState` has the following fields:
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'last_state_recalculation_slot': 'uint64',
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# Last finalized slot
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'last_finalized_slot': 'uint64',
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# Last justified slot
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'last_justified_slot': 'uint64',
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# Justification source
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'justification_source': 'uint64',
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'prev_cycle_justification_source': 'uint64',
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# Recent justified slot bitmask
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'justified_slot_bitfield': 'uint64',
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# Committee members and their assigned shard, per slot
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'shard_and_committee_for_slots': [[ShardAndCommittee]],
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# Persistent shard committees
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@ -666,7 +669,9 @@ def on_startup(initial_validator_entries: List[Any], genesis_time: uint64, pow_h
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crosslinks=crosslinks,
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last_state_recalculation_slot=0,
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last_finalized_slot=0,
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last_justified_slot=0,
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justification_source=0,
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prev_cycle_justification_source=0,
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justified_slot_bitfield=0,
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shard_and_committee_for_slots=x + x,
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persistent_committees=split(shuffle(validators, bytes([0] * 32)), SHARD_COUNT),
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persistent_committee_reassignments=[],
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@ -771,59 +776,6 @@ def exit_validator(index, state, block, penalize, current_slot):
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add_validator_set_change_record(state, index, validator.pubkey, EXIT)
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```
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## On startup
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Run the following code:
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```python
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def on_startup(initial_validator_entries: List[Any]) -> BeaconState:
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# Induct validators
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validators = []
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for pubkey, proof_of_possession, withdrawal_shard, withdrawal_address, \
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randao_commitment in initial_validator_entries:
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add_validator(
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validators=validators,
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pubkey=pubkey,
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proof_of_possession=proof_of_possession,
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withdrawal_shard=withdrawal_shard,
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withdrawal_address=withdrawal_address,
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randao_commitment=randao_commitment,
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current_slot=0,
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status=ACTIVE,
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)
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# Setup state
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x = get_new_shuffling(bytes([0] * 32), validators, 0)
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crosslinks = [
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CrosslinkRecord(
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slot=0,
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hash=bytes([0] * 32)
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)
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for i in range(SHARD_COUNT)
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]
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state = BeaconState(
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validator_set_change_slot=0,
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validators=validators,
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crosslinks=crosslinks,
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last_state_recalculation_slot=0,
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last_finalized_slot=0,
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last_justified_slot=0,
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shard_and_committee_for_slots=x + x,
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persistent_committees=split(shuffle(validators, bytes([0] * 32)), SHARD_COUNT),
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persistent_committee_reassignments=[],
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deposits_penalized_in_period=[],
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next_shuffling_seed=b'\x00'*32,
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validator_set_delta_hash_chain=bytes([0] * 32), # stub
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pre_fork_version=INITIAL_FORK_VERSION,
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post_fork_version=INITIAL_FORK_VERSION,
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fork_slot_number=0,
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pending_attestations=[],
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recent_block_hashes=[bytes([0] * 32) for _ in range(CYCLE_LENGTH * 2)],
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randao_mix=bytes([0] * 32) # stub
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)
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return state
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```
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## Per-block processing
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This procedure should be carried out every beacon block.
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@ -860,7 +812,7 @@ def update_ancestor_hashes(parent_ancestor_hashes: List[Hash32],
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For each `AttestationRecord` object `obj`:
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* Verify that `slot <= block.slot - MIN_ATTESTATION_INCLUSION_DELAY` and `slot >= max(parent.slot - CYCLE_LENGTH + 1, 0)`.
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* Verify that `justified_slot` is equal to or earlier than `last_justified_slot`.
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* Verify that `justified_slot` is equal to `justification_source if slot >= block.slot - (block.slot % CYCLE_LENGTH) else prev_cycle_justification_source`
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* Verify that `justified_block_hash` is the hash of the block in the current chain at the slot -- `justified_slot`.
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* Verify that either `last_crosslink_hash` or `shard_block_hash` equals `state.crosslinks[shard].shard_block_hash`.
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* Compute `full_parent_hashes` = `[get_block_hash(state, block, slot - CYCLE_LENGTH + i) for i in range(1, CYCLE_LENGTH - len(parent_hashes) + 1)] + parent_hashes` (eg, if `CYCLE_LENGTH = 4`, `slot = 5`, the actual block hashes starting from slot 0 are `Z A B C D E F G H I J`, and `parent_hashes = [D', E']` then `parent_hashes = [B, C, D' E']`). Note that when *creating* an attestation for a block, the hash of that block itself won't yet be in the `state`, so you would need to add it explicitly.
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@ -987,13 +939,22 @@ _Note: `last_state_recalculation_slot` will always be a multiple of `CYCLE_LENGT
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* Let `total_balance = sum([v.balance for v in active_validators])`
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* Let `this_cycle_attestations = [a for a in state.pending_attestations if s <= a.slot < s + CYCLE_LENGTH]` (note: this is the set of attestations _of slots in the cycle `s...s+CYCLE_LENGTH-1`_, not attestations _that got included in the chain during the cycle `s...s+CYCLE_LENGTH-1`_)
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* Let `prev_cycle_attestations = [a for a in state.pending_attestations if s - CYCLE_LENGTH <= a.slot < s]
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* Let `this_cycle_s_attestations = [a for a in this_cycle_attestations if get_block_hash(state, block, s) in a.parent_hashes]
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* Let `this_cycle_s_attestations = [a for a in this_cycle_attestations if get_block_hash(state, block, s) in a.parent_hashes and a.justified_slot == state.justification_source]
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* Let `prev_s_attestations = [a for a in this_cycle_attestations + prev_cycle_attestations if get_block_hash(state, block, s - CYCLE_LENGTH) in a.parent_hashes and a.justified_slot == state.prev_cycle_justification_source]
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* Let `s_attesters` be the union of the validator index sets given by `[get_attestation_participants(state, a) for a in this_cycle_s_attestations]`
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* Let `prev_s_attesters` be the union of the validator index sets given by `[get_attestation_participants(state, a) for a in this_cycle_s_attestations]`
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* Let `total_balance_attesting_at_s = sum([v.balance for v in s_attesters])`
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* Let `total_balance_attesting_at_prev_s = sum([v.balance for v in prev_s_attesters])`
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#### Adjust justified slots and crosslink status
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* If `3 * total_balance_attesting_at_s >= 2 * total_balance` then first (i) if `last_justified_slot == s - CYCLE_LENGTH`, set `last_finalized_slot = last_justified_slot`, then (ii) set `last_justified_slot = s`.
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* Set `state.justified_slot_bitfield = (state.justified_slot_bitfield * 2) % 2**64`.
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* If `3 * total_balance_attesting_at_prev_s >= 2 * total_balance` then set `state.justified_slot_bitfield &= 2` (ie. flip the second lowest bit to 1) and `new_justification_source = prev_s`.
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* If `3 * total_balance_attesting_at_s >= 2 * total_balance` then set `state.justified_slot_bitfield &= 1` (ie. flip the lowest bit to 1) and `new_justification_source = s`.
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* If `justification_source == prev_s and state.justified_slot_bitfield % 4 == 3`, set `last_finalized_slot = justification_source`.
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* If `justification_source == prev_s - 2 * CYCLE_LENGTH and state.justified_slot_bitfield % 16 in (15, 14)`, set `last_finalized_slot = justification_source`.
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* If `justification_source == prev_s - CYCLE_LENGTH and state.justified_slot_bitfield % 8 == 7`, set `last_finalized_slot = justification_source`.
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* Set `prev_cycle_justification_source = justification_source` and `justification_source = new_justification_source`.
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For every `(shard, shard_block_hash)` tuple:
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