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Added dependencies to fork choice section

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vbuterin 2020-12-10 14:48:57 +08:00 committed by protolambda
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specs/phase1/fork-choice.md
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@ -22,87 +22,28 @@
## Introduction ## Introduction
This document is the beacon chain fork choice spec for part of Ethereum 2.0 Phase 1. This document is the beacon chain fork choice spec for part of Ethereum 2.0 Phase 1. The only change that we add from phase 0 is that we add a concept of "data dependencies"; a block is only eligible for consideration in the fork choice after a data availability test has been successfully completed for all dependencies. The "root" of a shard block for data dependency purposes is considered to be a DataCommitment object, which is a pair of a Kate commitment and a length.
### Updated data structures ## Dependency calculation
#### Extended `Store`
```python ```python
@dataclass def get_new_dependencies(state: BeaconState) -> Set[DataCommitment]:
class Store(object): return set(
time: uint64 # Already confirmed during this epoch
genesis_time: uint64 [c.commitment for c in state.current_epoch_pending_headers if c.confirmed] +
justified_checkpoint: Checkpoint # Already confirmed during previous epoch
finalized_checkpoint: Checkpoint [c.commitment for c in state.previous_epoch_pending_headers if c.confirmed] +
best_justified_checkpoint: Checkpoint # Confirmed in the epoch before the previous
blocks: Dict[Root, BeaconBlock] = field(default_factory=dict) [c for c in shard for shard in state.most_recent_confirmed_commitments if c != DataCommitment()]
block_states: Dict[Root, BeaconState] = field(default_factory=dict)
checkpoint_states: Dict[Checkpoint, BeaconState] = field(default_factory=dict)
latest_messages: Dict[ValidatorIndex, LatestMessage] = field(default_factory=dict)
shard_stores: Dict[Shard, ShardStore] = field(default_factory=dict)
```
### New data structures
#### `ShardLatestMessage`
```python
@dataclass(eq=True, frozen=True)
class ShardLatestMessage(object):
epoch: Epoch
root: Root
```
#### `ShardStore`
```python
@dataclass
class ShardStore:
shard: Shard
signed_blocks: Dict[Root, SignedShardBlock] = field(default_factory=dict)
block_states: Dict[Root, ShardState] = field(default_factory=dict)
latest_messages: Dict[ValidatorIndex, ShardLatestMessage] = field(default_factory=dict)
```
### Updated helpers
#### Updated `get_forkchoice_store`
```python
def get_forkchoice_store(anchor_state: BeaconState, anchor_block: BeaconBlock) -> Store:
assert anchor_block.state_root == hash_tree_root(anchor_state)
anchor_root = hash_tree_root(anchor_block)
anchor_epoch = get_current_epoch(anchor_state)
justified_checkpoint = Checkpoint(epoch=anchor_epoch, root=anchor_root)
finalized_checkpoint = Checkpoint(epoch=anchor_epoch, root=anchor_root)
return Store(
time=anchor_state.genesis_time + SECONDS_PER_SLOT * anchor_state.slot,
genesis_time=anchor_state.genesis_time,
justified_checkpoint=justified_checkpoint,
finalized_checkpoint=finalized_checkpoint,
best_justified_checkpoint=justified_checkpoint,
blocks={anchor_root: copy(anchor_block)},
block_states={anchor_root: anchor_state.copy()},
checkpoint_states={justified_checkpoint: anchor_state.copy()},
shard_stores={
Shard(shard): get_forkchoice_shard_store(anchor_state, Shard(shard))
for shard in range(get_active_shard_count(anchor_state))
}
) )
``` ```
#### Updated `update_latest_messages`
```python ```python
def update_latest_messages(store: Store, attesting_indices: Sequence[ValidatorIndex], attestation: Attestation) -> None: def get_all_dependencies(store: Store, block: BeaconBlock) -> Set[DataCommitment]:
target = attestation.data.target if block.slot < SHARDING_FORK_SLOT:
beacon_block_root = attestation.data.beacon_block_root return set()
# TODO: separate shard chain vote else:
shard = attestation.data.shard latest = get_new_dependencies(store.block_states[hash_tree_root(block)])
for i in attesting_indices: older = get_all_dependencies(store, store.blocks[block.parent_root])
if i not in store.latest_messages or target.epoch > store.latest_messages[i].epoch: return latest.union(older)
store.latest_messages[i] = LatestMessage(epoch=target.epoch, root=beacon_block_root)
shard_latest_message = ShardLatestMessage(epoch=target.epoch, root=attestation.data.shard_head_root)
store.shard_stores[shard].latest_messages[i] = shard_latest_message
``` ```