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Finished epoch transition

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vbuterin 2019-03-01 19:49:28 -06:00 committed by GitHub
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specs/core/0_beacon-chain.md
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@ -137,6 +137,7 @@
- [Crosslinks](#crosslinks-1)
- [Ejections](#ejections)
- [Validator registry and shuffling seed data](#validator-registry-and-shuffling-seed-data)
- [Slashings and exit queue](#slashings-and-exit-queue)
- [Final updates](#final-updates)
- [State root verification](#state-root-verification)
- [References](#references)
@ -2093,18 +2094,21 @@ def process_ejections(state: BeaconState) -> None:
#### Validator registry and shuffling seed data
First, update the following:
* Set `state.previous_shuffling_epoch = state.current_shuffling_epoch`.
* Set `state.previous_shuffling_start_shard = state.current_shuffling_start_shard`.
* Set `state.previous_shuffling_seed = state.current_shuffling_seed`.
If the following are satisfied:
* `state.finalized_epoch > state.validator_registry_update_epoch`
* `state.latest_crosslinks[shard].epoch > state.validator_registry_update_epoch` for every shard number `shard` in `[(state.current_shuffling_start_shard + i) % SHARD_COUNT for i in range(get_current_epoch_committee_count(state))]` (that is, for every shard in the current committees)
update the validator registry and associated fields by running
```python
def should_update_validator_registry(state: BeaconState) -> bool:
# Must have finalized a new block
if state.finalized_epoch <= state.validator_registry_update_epoch:
return False
# Must have processed new crosslinks on all shards of the current epoch
shards_to_check [
(state.current_shuffling_start_shard + i) % SHARD_COUNT
for i in range(get_current_epoch_committee_count(state))
]
for shard in shards_to_check:
if state.latest_crosslinks[shard].epoch <= state.validator_registry_update_epoch:
return False
return True
```
```python
def update_validator_registry(state: BeaconState) -> None:
@ -2151,23 +2155,38 @@ def update_validator_registry(state: BeaconState) -> None:
state.validator_registry_update_epoch = current_epoch
```
and perform the following updates:
Run the following function:
* Set `state.current_shuffling_epoch = next_epoch`
* Set `state.current_shuffling_start_shard = (state.current_shuffling_start_shard + get_current_epoch_committee_count(state)) % SHARD_COUNT`
* Set `state.current_shuffling_seed = generate_seed(state, state.current_shuffling_epoch)`
If a validator registry update does _not_ happen do the following:
* Let `epochs_since_last_registry_update = current_epoch - state.validator_registry_update_epoch`.
* If `epochs_since_last_registry_update > 1` and `is_power_of_two(epochs_since_last_registry_update)`:
* Set `state.current_shuffling_epoch = next_epoch`.
* Set `state.current_shuffling_seed = generate_seed(state, state.current_shuffling_epoch)`
* _Note_ that `state.current_shuffling_start_shard` is left unchanged.
```python
def update_registry_and_shuffling_data(state: BeaconState) -> None:
# First set previous shuffling data to current shuffling data
state.previous_shuffling_epoch = state.current_shuffling_epoch
state.previous_shuffling_start_shard = state.current_shuffling_start_shard
state.previous_shuffling_seed = state.current_shuffling_seed
# Check if we should update, and if so, update
if should_update_validator_registry(state):
update_validator_registry(state)
# If we update the registry, update the shuffling data and shards as well
state.current_shuffling_epoch = next_epoch
state.current_shuffling_start_shard = (
state.current_shuffling_start_shard +
get_current_epoch_committee_count(state)) % SHARD_COUNT
)
state.current_shuffling_seed = generate_seed(state, state.current_shuffling_epoch)
else:
# If processing at least one crosslink keeps failing, then reshuffle every power of two,
# but don't update the current_shuffling_start_shard
epochs_since_last_registry_update = current_epoch - state.validator_registry_update_epoch
if epochs_since_last_registry_update > 1 and is_power_of_two(epochs_since_last_registry_update):
state.current_shuffling_epoch = next_epoch
state.current_shuffling_seed = generate_seed(state, state.current_shuffling_epoch)
```
**Invariant**: the active index root that is hashed into the shuffling seed actually is the `hash_tree_root` of the validator set that is used for that epoch.
Regardless of whether or not a validator set change happens run `process_slashings(state)` and `process_exit_queue(state)`:
#### Slashings and exit queue
Run `process_slashings(state)` and `process_exit_queue(state)`:
```python
def process_slashings(state: BeaconState) -> None:
@ -2218,10 +2237,29 @@ def process_exit_queue(state: BeaconState) -> None:
#### Final updates
* Set `state.latest_active_index_roots[(next_epoch + ACTIVATION_EXIT_DELAY) % LATEST_ACTIVE_INDEX_ROOTS_LENGTH] = hash_tree_root(get_active_validator_indices(state.validator_registry, next_epoch + ACTIVATION_EXIT_DELAY))`.
* Set `state.latest_slashed_balances[next_epoch % LATEST_SLASHED_EXIT_LENGTH] = state.latest_slashed_balances[current_epoch % LATEST_SLASHED_EXIT_LENGTH]`.
* Set `state.latest_randao_mixes[next_epoch % LATEST_RANDAO_MIXES_LENGTH] = get_randao_mix(state, current_epoch)`.
* Remove any `attestation` in `state.latest_attestations` such that `slot_to_epoch(attestation.data.slot) < current_epoch`.
Run the following function:
```python
def finish_epoch_update(state: BeaconState) -> None:
current_epoch = get_current_epoch(state)
next_epoch = current_epoch + 1
# Set active index root
index_root_position = (next_epoch + ACTIVATION_EXIT_DELAY) % LATEST_ACTIVE_INDEX_ROOTS_LENGTH
state.latest_active_index_roots[index_root_position] = hash_tree_root(
get_active_validator_indices(state.validator_registry, next_epoch + ACTIVATION_EXIT_DELAY)
)
# Set total slashed balances
state.latest_slashed_balances[next_epoch % LATEST_SLASHED_EXIT_LENGTH] = (
state.latest_slashed_balances[current_epoch % LATEST_SLASHED_EXIT_LENGTH]
)
# Set randao mix
state.latest_randao_mixes[next_epoch % LATEST_RANDAO_MIXES_LENGTH] = get_randao_mix(state, current_epoch)
# Remove previous epoch attestations
state.latest_attestations = [
a for a in state.latest_attestations if
slot_to_epoch(attestation.data.slot) == current_epoch
]
```
### State root verification